Cultivation & Maintenance (Grass)

GRASSES ARE EASY TO GROW. Individual species are often tolerant of a wide range of climatic and cultural conditions, and the great diversity of grasses means there are species and cultivated varieties suited for almost any purpose and place. Properly selected and used, grasses and their relatives can contribute more beauty and sustained interest with less maintenance than almost any other group of herbaceous landscape plants. This topic offers general concepts, techniques, and recommendations for cultivating and maintaining grasses.

Fitting Plants to Purpose and Place

When selecting grasses for gardens and other managed landscapes, aesthetic considerations are ultimately a matter of personal choice; however, there are practical and environmental points worth considering that are independent of style and taste. Traditional gardening often attempts to fit place to plants, using horticultural techniques to alter growing conditions so that otherwise minimally adapted plants may survive. In some cases these techniques can successfully alter the local or micro-habitat more or less permanently, allowing the chosen plants to thrive without the continual input of additional resources. In many cases, fitting place to plants results in a permanent dependency upon supplemental irrigation and often necessitates the continual renewal, support, or wholesale replacement of the plants themselves. A more environmentally friendly approach is to fit plants to place: Know your climate and local conditions, and choose plants that are appropriately adapted. If low maintenance is one of the purposes of your planting, this approach will be more rewarding.

The Importance of Provenance

Provenance literally means derivation or place of origin. In an ecological context the term is an important one because it goes beyond the broad meaning of the word native and refers to the origin of the specific plants in question. For example, switchgrass, Panicum virgatum, is a wide-ranging species that naturally occurs in prairies and on open ground, woods, and freshwater and brackish marshes from eastern Canada through most of the United States except for California and the Pacific Northwest south to Mexico and Central America. This is the native range of the species, and it is correct to say that P. virgatum is native to these places. Like most wide-ranging species, P. virgatum is highly variable in its genetic makeup, and it is obvious to any casual observer that plants from different parts of the range are often quite unique from one another in a number of characteristics. The term provenance refers to this unique origin. For example, plants of P. virgatum originating from the sandy outer coastal plain of New Jersey are of different provenance than plants originating from interior East Texas.

Provenance can be of profound importance to the suitability and fitness of plants for garden and landscape purposes. For example, Indian grass, Sorghastrum nutans, has a native range over much of central and eastern North America. There’s a much higher incidence of glaucous-blue foliage among plants of central (prairie) provenance than among plants of eastern provenance, which are typically green-leaved. In addition to the obvious difference in foliage color, Indian grasses of prairie provenance are typically taller and more lax-stemmed than plants of eastern provenance. Planting plants of prairie provenance in an eastern landscape is likely to result in attractively blue-leaved plants that unattractively flop on the ground.

Provenance matters. These switchgrasses, Panicum virgatum, growing unplanted along a road outside Dallas represent the local population of this species. The dry, sunny Texas provenance of these particular plants makes it likely that they possess more genetically inherent heat tolerance than cool northern representatives of P. virgatum.

Provenance matters. These switchgrasses, Panicum virgatum, growing unplanted along a road outside Dallas represent the local population of this species. The dry, sunny Texas provenance of these particular plants makes it likely that they possess more genetically inherent heat tolerance than cool northern representatives of P. virgatum.

Characteristics associated with provenance can sometimes be overcome with individual selection. For example, I selected an upright-growing glaucous-blue individual from a multitude of seedling plants of prairie provenance and introduced it as Sorghastrum nutans ‘Sioux Blue’, a cultivated variety (cul-tivar) which must be vegetatively propagated if it is to retain its especially blue color and upright character. Vegetative (clonal) cultivars often reflect characteristics associated with their original provenance. Panicum virgatum ‘Cloud Nine’, originally of northeastern North American provenance, is green and relatively thin-leaved, while ‘Dallas Blues’, selected from plants of Texas provenance, is glaucous blue with thick, coarse foliage.

Heat tolerance and cold hardiness are among other characteristics of practical import that often vary with provenance. For example, the documented native range of purple muhly grass, Muhlenbergia capillaris, extends from New England to the Gulf coast. Individual plants are more likely to survive winters in New Jersey if they are of more northern provenance.

In addition to readily visible characters, provenance entails a huge number of variables that are obscure but of paramount importance to the relative balance of regional and local ecologies, and for this reason it is best to seek plants of local provenance when introducing grasses into otherwise intact habitats. The commercial availability of grasses of known provenance is increasing along with awareness of these issues.

Cool-season and Warm-season Grasses

Flowering plants in general, including grasses, can be grouped into two broad categories: cool-season species and warm-season species. Scientifically speaking, cool-season grasses are included in C3 plants, and warm-season grasses are in with C4 plants. Both C3 and C4 plants use light energy to make sugar from water and carbon dioxide, and this sugar is used to fuel growth. The designations C3 and C4 refer to molecular compounds produced during photosynthesis. C3 plants fix carbon dioxide in a three-carbon compound that is then transformed into glucose (sugar). C4 plants do this too, but first they create a four-carbon intermediary compound. The C4 process is ultimately the most efficient, accounting for the sometimes phenomenal growth capacity of C4 plants; however, it requires relatively high temperatures, hence the warm- season designation. C3 plants are less efficient overall than C4 plants but excel at lower temperatures.

Seedlings of Gahnia setifolia, a New Zealand native sedge, are labeled by the provenance at Taupo Native Plant Nursery on the North Island. The forty-year-old nursery originated as part of the Department of Conservation and continues as a successful commercial business specializing in New Zealand native plants of documented origin, producing nearly two million plants annually.

Seedlings of Gahnia setifolia, a New Zealand native sedge, are labeled by the provenance at Taupo Native Plant Nursery on the North Island. The forty-year-old nursery originated as part of the Department of Conservation and continues as a successful commercial business specializing in New Zealand native plants of documented origin, producing nearly two million plants annually.

One additional physiological difference affecting relative heat tolerance and moisture efficiency is that cool-season grasses open their pores to take in carbon dioxide during the day, which exposes them to warm drying winds and subsequent moisture loss. Warm-season grasses can take in carbon dioxide at night, opening their pores when temperatures are cooler and moisture loss is lessened.

Optimum growth of cool-season grasses occurs under relatively moist conditions when soil temperatures are between 50° and 65°F (10° and 18°C) and air temperatures are between 60° and 75°F (16° and 24°C). In a cold-temperate climate, this means cool-season grasses often have two periods of growth. A typical cool-season grass begins growth in late winter, develops significant foliage by early spring, and produces flowers anytime from late winter to early summer. As summer progresses, decreasing rainfall and increasing temperatures work against photosynthetic efficiency and cause physiological stress which results in partial or complete summer dormancy. Cool-season grasses resume growth when autumn brings increased moisture and lower temperatures.

Cool-season grasses may be divided or transplanted in winter or early spring, and again in late summer and autumn. They should not be moved or divided as they approach or are in their summer dormant state, however partial it may be, since the additional stress may prove fatal. Heat stress can be relieved to some extent by providing summer shade, and supplemental irrigation during summer droughts will also reduce stress. Summer watering can keep some species from going dormant, although this is not the most wa-terwise approach to gardening. In mild, cool climates, cool-season grasses may be evergreen or semievergreen. Cool-season grasses include most Ach-natherum, Calamagrostis, Fescue, Helictotrichon, Koeleria, Melica, Milium, Poa, and Stipa species as well as the common bluegrasses, fescues, and ryegrasses so often used as lawn grasses and the cereal grasses wheat and rice.

Warm-season grasses like it hot. They achieve optimum growth when soil temperatures range between 70° and 90°F (21° and 32°C) and in air temperatures of 80° to 95°F (26° to 35°C), and are much less susceptible to drought stress. In cold-temperate climates, warm-season growers typically break winter dormancy quite late in spring, and are very slow-growing until real summer heat arrives. They revel in the intense summer sun, growing steadily larger and gathering energy for flowering at summer’s end. Their processes shut down with the onset of cold weather, and they remain dormant through winter. During this shut-down many warm-season grasses take on beautiful autumn colors.

Warm-season grasses are best divided or transplanted when they are in active growth but long before they begin blooming. In cold-temperate climates, late spring into early summer are ideal times, although summer division and transplanting are practical if moisture is sufficiently high. It can be risky to divide or transplant warm-season grasses in late fall since much of the plants’ stored energy has often just been spent on flower and seed production. In cold climates, late fall divisions and transplants will make very little root growth before winter dormancy begins, and plants may succumb to the stress of winter cold and the often oxygen-deprived conditions of frozen soils. Small transplants and plugs run a high risk of popping out of the ground due to frost-heaving. Fall transplanting of warm-season grasses will be most successful in mild climates and least successful in climates where winter low temperatures are nearer to the grasses’ normal limits of cold hardiness

Warm-season grass genera include Arundo, Blepharoneuron, Bothriochloa, Cortaderia, Eragrostis, Imperata, Melinis, Miscanthus, Muhlenbergia, Pennisetum, Setaria, Tridens, Tripsacum, Saccharum, and Uniola, as well as the majority of North American prairie genera including Andropogon, Bouteloua, Panicum, Schizachyrium, Sorghastrum, Spartina, and Sporobolus. Corn (maize), sorghum, millet, and sugarcane are other examples of warm-season grasses.

Hardiness

These zones are based on annual average minimum temperatures recorded in the United States and must be interpreted cautiously. Though such zones are useful measures, they tend to reinforce the notion that hardiness is limited solely by plants’ ability to survive cold. In many garden situations, other factors such as sustained heat, poorly drained or aerated soils, or extremes of acidity or alkalinity may actually be more determining of plants’ long-term hardiness in a given location.

Melica californica in late June. right Melica californica in early April.

Melica californica in late June. right Melica californica in early April.

Indian grass, Sorghastrum nutans, is a classic warm-season grass, shown here in peak bloom on 26 August, in the full heat of summer in eastern Pennsylvania. Indian grass begins growth late in spring.

Indian grass, Sorghastrum nutans, is a classic warm-season grass, shown here in peak bloom on 26 August, in the full heat of summer in eastern Pennsylvania. Indian grass begins growth late in spring.

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California melic, Melica californica, is a cool-season grass, flowering in spring when the weather is cool and moisture is abundant, then going dormant with the arrival of summer heat and dryness. These two photos capture different angles of the same planting at Leaning Pine Arboretum in San Luis Obispo, California.

When plants are introduced from distant parts of the world they are typically subjected to climatic patterns that differ from their own, even though the average minimum low temperatures may be similar. For example, temperatures in Japan rise fairly steadily from winter through spring. Spring warming in eastern North America is usually interrupted by brief, late periods of freezing cold. Similarly, the eastern North American autumn is much more uneven in its cooling than is Japan’s. Unaccustomed to these patterns, Japanese species in North American gardens are sometimes adversely affected.

The winter hardiness of cool-season growers may ultimately be dependent upon the extent of their exposure to high temperatures during summer days and nights. Cool-season species that are tolerant of extreme low temperatures in their original climate sometimes succumb during relatively mild winters in a foreign garden because they enter winter weakened by excessive summer heat or drought. Conversely, the winter cold hardiness of warm-season species can be seriously reduced if summer temperatures and sunlight intensity are not high enough to adequately drive their metabolisms. This partly explains why plants may prove hardy through winters in a truly cold place and succumb during a milder winter in a different climate. For example, the striped giant reed, Arundo donax ‘Variegata’, is winter hardy only in warmer parts of England, yet is hardy in the U.S. mid Atlantic region, which is much colder in winter but much hotter in summer.

Snowfall also dramatically influences grasses’ winter survival. A steady cover of snow often protects soil temperatures from dipping significantly below freezing during periods when air temperatures may drop to lethal lows. This important variable is not reflected in the hardiness zone map.

Never underestimate the importance of microclimate. Any garden or landscape is likely to include special niches with growing conditions that are effectively different from the regional climate. Sheltered corners, planting beds adjacent to warm walls of a dwelling, interior courtyards, or even roof gardens can afford the opportunity to enjoy grasses that might not normally be considered hardy.

Of necessity, the hardiness zones listed in topics and nursery catalogs are often educated guesses rather than documented fact. Despite considerable research in recent years there is still much to be done on heat and cold hardiness of grasses, and this is especially true for grasses grown outside their usual limits of distribution.

Sunlight

The majority of true grasses (Poaceae), cattails, and most restios thrive in sunny situations, and wood rushes and many sedges prefer shade; however, there are many exceptions.

The amount of sun required or tolerated for optimum growth is not easily quantified. The intensity of full sun varies dramatically in different parts of the world. Full sun in Devon, England, is more like partial shade in Southern California. Full sun at high mountain elevations, which are often cloaked in clouds, may equate to shade in a valley bottom. Available moisture and relative fertility of the soil or growing medium can also strongly influence the ideal amount of sunlight. For example, a particular grass may grow largest and flower most fully in direct, all-day sun if the roots are constantly moist, yet the same grass may require partial shade for mere survival in an extremely dry environment. Despite these qualifications, it is reasonable to say that most sun-loving grasses will achieve adequate growth and flowering if provided approximately five hours of direct sunlight daily during the growing season. They will be stronger and more upright with more sun and smaller and more lax in less.

In addition to the intensity of sun, the seasonal duration of sunlight and the number of daylight hours also affect growth and flowering. Some grasses require longer growing seasons than others to complete their flowering and fruiting cycles. Most temperate grasses and sedges also have what is known as a dual-daylight requirement for flowering. For some species this means they must be exposed to short days followed by longer days. For others, long days followed by shorter days trigger flowering.

Species that prefer shade generally prefer deciduous or variable shade: very few thrive in the constant dimness of evergreen forest interiors. For evergreen species of grasses and their relatives, the sunlight they receive in winter is often necessary to their survival, though too much winter sun can prove desiccating and injurious.

Moisture

Although standing with hose in hand still seems to be a popular form of therapy, there are better ways to relax in the garden. The ability to thrive without constant watering and, in many cases, without any supplemental irrigation at all is part of the appeal and beautiful utility of grasses. Other than the watering of new transplants, which cannot be avoided, gardeners can do much to free themselves from the waste and tedium of watering by properly selecting and siting grasses.

Moisture requirements and tolerance can vary dramatically even between species in the same genus. In this mid-October view in a West Virginia deciduous woodlands, silver sedge, Carexplatyphylla, grows naturally in thin, rocky, alkaline soil that is periodically bone dry.

Moisture requirements and tolerance can vary dramatically even between species in the same genus. In this mid-October view in a West Virginia deciduous woodlands, silver sedge, Carexplatyphylla, grows naturally in thin, rocky, alkaline soil that is periodically bone dry.

Tussock sedge, Carex stricta, naturally occurs in wet habitats such as this red maple swamp in northern Delaware, photographed in early April, but it is a very adaptable species and can survive in soils that are barely moist.

Tussock sedge, Carex stricta, naturally occurs in wet habitats such as this red maple swamp in northern Delaware, photographed in early April, but it is a very adaptable species and can survive in soils that are barely moist.

The available moisture typically present in a plant’s native habitat is a good rule of thumb for gauging needed moisture in a designed or managed landscape, and the least costly and least disruptive approach is to try to match plants to similar existing conditions. Often the available moisture on a constructed or highly modified landscape is less than that of many natural habitats. In this case it is more water-conserving to consider species adapted to dry environments than to introduce artificial irrigation. In other landscape situations, the challenge may be too much moisture, and again, appropriate selection of grasses can often provide the solution. Many species of true grasses, sedges, cattails, and restios are naturally adapted to moist or even partly inundated conditions, and these can contribute significantly to the multiseason beauty and habitat diversity of moist places and wetlands in and beyond the individual garden.

Soils and Fertility

One of the reasons grasses are being welcomed into all sorts of private and public landscapes is that they often thrive in difficult soils in which little else will grow. While many grasses appreciate a well-drained reasonably fertile loam, the most adaptable sorts are undaunted by either poorly drained heavy clays or dry infertile sands. As a group, grasses are also largely indifferent to normal variations in acidity and alkalinity, and many, including desert species and coastal species that have evolved in brackish conditions or near ocean spray, are significantly salt-tolerant. Species such as Carex humilis that have evolved in dry, alkaline soil conditions are naturally adapted to similar conditions that may be found on rooftops, between paving, walls, and other masonry structures.

Soil variations can, however, make a real difference in the health and manageability of certain species. For example, the blue fescues generally require sharp drainage if they are to survive cold, wet winters in good condition. Running grasses such as blue lyme grass, Leymus arenarius, or giant reed, Arundo donax, may be manageable in dense clays or sterile sand but too aggressive in rich friable loam. Some specialized species such as Fraser’s sedge, Cymophyllus frase-rianus, require well-aerated soils high in organic matter for long-term survival.

Except when grown on the most sterile soils and sands—and even then, only if they are not evolved from such conditions—grasses generally do not benefit from supplemental fertilization. Adding concentrated chemical fertilizers to average soils can actually hurt performance. Excess fertility results in overlush growth and is likely to cause plants to lose their shape and flop unmanageably. This is especially true in nutrient-efficient genera such as An-dropogon, Schizachyrium, and Sorghastrum. Staking large grasses to hold them upright is tedious in small gardens and impossibly impractical in large landscapes, and is unnecessary if fertility and moisture levels are maintained at appropriate levels. Running grasses that are easily managed in average soils can become aggressive nuisances in overrich soils. Grasses such as broom-sedge, Andropogon virginicus, that are specially adapted to infertile soils may lose their competitive edge and be overgrown by other plants if nutrient levels are raised significantly. Especially in cold-temperate regions, many invasive nongrass species thrive on elevated fertility. Taking advantage of the inherent ability of grasses to grow in infertile soils is one strategy for minimizing the need to control invasive nongrasses.

Growth Habits: Runners and Clumpers

Though all grasses increase in width or spread to some degree by lateral shoots, for practical purposes they can be categorized as either runners or clumpers. Running grasses spread rather rapidly by rhizomes (horizontal underground stems), in which case they may also be called rhizomatous grasses, or by stolons (horizontal aboveground stems), in which case they may be called stoloniferous.

A single genus may include both running and clumping species. For example, Miscanthus sinensis is clump-forming, while M. sacchariflorus is a strong runner. Pennisetum alopecuroides forms tight clumps, but P. incomptum spreads rapidly and extensively. The majority of running landscape grasses are rhi-zomatous. Stoloniferous growth is more common among turfgrasses.

Appropriately utilized, running grasses can minimize maintenance. Their ability to knit together and cover large areas often makes them the best choice for groundcover use and soil stabilization. Running grasses can fill gaps that may appear in a planting due to physical damage or disease, and many produce such dense growth that they effectively prevent weeds from establishing. In difficult sites such as dry urban traffic islands, durable running grasses are often the most practical choice. Some running species such as cordgrass, Spartina pectinata, and manna grass, Glyceria maxima, are adapted to moist or wet soils, and are suited for vegetating and stabilizing margins of ponds and storm water catchments or streambanks.

Planted in the wrong situation, running grasses can be seriously disruptive, overpowering less vigorous neighbors and turning once-diverse landscapes into monocultures. Before planting a strongly running grass, carefully consider whether adjacent plantings and hardscapes will be sturdy enough to contain its spread, and whether resources are available to control any unplanned advances into unwanted areas.

The growth rate of running species varies radically with climate and cultural conditions. For example, a warm-season spreader such as giant reed, Arundo donax, may be unmanageable in a small garden in sunny South Carolina; however, the relatively short, cool season of a Connecticut garden may slow it to the point that it behaves nearly like a clumping grass.

Clumping grasses essentially remain in place. They may slowly increase in girth, but new shoots will not appear at significant distances from the clump. Grasses that produce tight clumps may also be referred to as tufted, cespitose, or bunchgrasses. Though clump-forming grasses may take years to reach mature size, the ultimate space they’ll occupy is predictable, and for this reason they are sometimes easier to plan for than running types. Because they don’t readily fill gaps, clump-formers used as groundcovers should be selected from species or cultivars of proven durability under local conditions.

Some grasses don’t fit neatly into either the running or clumping categories. The growth habit of Hakone grass, Hakonechloa macra, has been variously described as clumping or spreading. This species does increase by rhizomes and is capable of appreciable spread if cultural conditions are ideal, yet its rate of increase is often so modest that it is a clump-former in the practical sense. Switchgrass, Panicum virgatum, is another species that is somewhere between strictly clump-forming and running. Its rhizomes occasionally stray noticeably from the clump, yet for practical purposes it is a clumping grass.

Weediness and Ecological Invasiveness

There is a profound difference between plants which are weedy nuisances in gardens or other controlled landscapes and plants which have the potential to proliferate beyond human control, disrupting the balance of regional habitats or ecologies. Unfortunately, the word invasive is often used without qualification to describe both types of behavior. The subject is important enough to warrant greater precision. Both types of behavior—weediness and ecological invasiveness—are undesirable; however, ecological invasiveness can have far-reaching destructive impact in addition to being hugely costly to reverse or control. Guided by global perspective, realistic, preventative strategies must be developed with knowledge of local and regional conditions.

A weed in the simplest definition is a plant out of place. Grasses occasionally become weeds in gardens and other designed or highly managed landscapes by running aggressively or by self-sowing. Running species that have exceeded their limits can present a minor task easily accomplished with hand tools, or a major effort requiring power machinery and/or chemical herbicides. There are purposes for which even the most aggressively running species may be appropriate, such as contained spaces within sturdy masonry patios, terraces, and traffic islands, but it is important to gauge the potential for uncontrolled spreading prior to planting.

Though annual grasses have a well-earned reputation for weedy self-sowing, most perennial grasses in this topic are well behaved if appropriately selected and sited. In the garden, there are a few simple ways to minimize maintenance resulting from self-sown grasses. Removing the inflorescences of grasses before seeds ripen is the surest way of eliminating self-sowing, but this method robs the landscape of considerable beauty.

One way to avoid unwanted seedlings is to select species or cultivars that are not likely to produce fertile seed in your region or climate. For example, Karl Foerster’s feather-reed grass, Calamagrostis x acutiflora ‘Karl Foerster’, is essentially seed-sterile and can be planted without any real risk of self-sowing. Cultivars of Miscanthus sinensis vary greatly in the length of growing season required for the production of fertile seed. Choosing long-season cultivars for use in regions with short seasons can eliminate the possibility of self-sowing.

Another way to reduce self-sowing is to avoid excessive irrigation. Gravel or stone mulches will both reduce the amount of self-seeding and make it easier to spot and remove seedlings if they occur.

The potential of cultivated grasses to become ecologically invasive, disrupting local or regional ecosystems, is a serious, complicated issue. The capacity for invasiveness in any given grass species varies significantly with the unique genetic makeup of different ecotypes and is always a matter of how the inherent reproductive characteristics of the grass fit with available growing niches. All ecosystems are constantly in flux, with stability always relative. At their worst, ecologically invasive species, including grasses, rapidly disrupt this relative balance by displacing integral elements and causing changes in conditions leading to reduced diversity. Human activity is responsible for the majority of ecological imbalances that are increasingly evident, both by the relocation of species and by the disturbance or wholesale modification of regional environments.

The argument against plant introduction and dissemination is often framed by the broadly opposing terms native and exotic, but this is too superficial. The term native is often so imprecisely used as to be meaningless, and in any case, introducing a species from as little as 50 miles (80 km) away can result in habitat disruption. There is no one rule to go by; however, it is always advisable to be informed about local conditions and dynamics before introducing fertile grass species to designed landscapes adjacent to vulnerable local habitats.

Uncontained by masonry or other suitable barriers to its aggressive growth, spreading fountain grass, Pennis-etum incomptum, moves beyond the border and across the lawn in this late-August view of a Delaware public landscape.

Uncontained by masonry or other suitable barriers to its aggressive growth, spreading fountain grass, Pennis-etum incomptum, moves beyond the border and across the lawn in this late-August view of a Delaware public landscape.

Excessive overhead watering encourages wild-oat, Chasmanthium latifolium, to self-sow into constantly moist organic mulch in this early June view in a Pennsylvania public garden.

Excessive overhead watering encourages wild-oat, Chasmanthium latifolium, to self-sow into constantly moist organic mulch in this early June view in a Pennsylvania public garden.

Remember that ecologically invasive behavior is a combination of the right plant in the wrong conditions. Purple pampas grass, Cortaderia jubata, is a balanced element in the mountains of Chile, Ecuador, and Peru, where it evolved, but it has proved too well adapted to coastal mountains in California, where it is aggressively out of balance. In some cases, exotic grasses have become naturalized, but their spread has been naturally limited to habitats created and maintained by human disturbance.

There are also numerous examples of cultivated grasses that have becoming seriously disruptive in certain parts of the world, yet these same species are completely innocuous elsewhere. For example, giant reed, Arundo donax, has widely escaped and established itself in warm, moist habitats in Southern California; however, in the cold northeastern United States it rarely flowers, never sets seed, and consequently poses little if any threat there. Miscanthus sinensis has proved itself to be a destructive force in moist bottomlands in the warm U.S. Southeast, yet it is completely benign in arid California where it will not even survive unless artificially irrigated.

Sometimes the term species is not specific enough to distinguish between plants prone to balance or imbalance. One of the most semantically perplexing examples involves common reed, Phragmites australis. This cosmopolitan species is native to North America’s mid Atlantic region and was once a relatively stable element in the regional ecology. European ecotypes of the same species, introduced inadvertently through human activity, have proved so fit for modern mid Atlantic conditions that this grass has spread over tens of thousands of acres. Using the accepted concept of species combined with native/exotic terminology, we can identify this invasive grass as an exotic form of a native species.

Introduced from its native habitat in the mountains of Chile, Ecuador, and Peru, purple pampas grass, Cortaderia jubata, has naturalized extensively in California's coastal mountains, displacing many local species that would otherwise occupy the same niche.

Introduced from its native habitat in the mountains of Chile, Ecuador, and Peru, purple pampas grass, Cortaderia jubata, has naturalized extensively in California’s coastal mountains, displacing many local species that would otherwise occupy the same niche.

Ravenna grass, Saccharum raven-nae, grows in a neat line parallel to active railroad tracks in Wilmington, Delaware. This exotic species has been cultivated in the United States for over a century, but it has so far proved capable of naturalizing only in greatly disturbed niches, such as here in the highly modified habitat created and maintained by human industrial activity.

Ravenna grass, Saccharum raven-nae, grows in a neat line parallel to active railroad tracks in Wilmington, Delaware. This exotic species has been cultivated in the United States for over a century, but it has so far proved capable of naturalizing only in greatly disturbed niches, such as here in the highly modified habitat created and maintained by human industrial activity.

Ethically responsible individual gardeners and public landscape professionals will seek rational ways to enjoy grasses and other introduced plants, while respecting the fragile balance of regional ecologies.

Pests and Diseases

Grasses are among the most pest-free and disease-free of all landscape plants. With appropriate selection, siting, and general cultural conditions that minimize stress, they will be nearly trouble-free.

Some grasses are susceptible to foliar rust diseases caused by fungi. Rusts produce orange or brownish discoloration on leaves and are most likely to be a problem during warm, humid seasons, especially on cool-season grasses. Rusts can be minimized or eliminated entirely by positioning susceptible grasses to maximize air movement around and through them, especially in warm periods. Rust diseases on grasses in the landscape are often temporary and usually tolerable. They can be most troublesome on grasses being propagated under greenhouse conditions, in which case chemical control with wetable sulfur or commercial fungicides may be advisable.

Miscanthus mealybug can be a serious pest but is restricted to Miscanthus species and cultivated varieties. The mealybug, Miscanthicoccus miscanthi, is an Asian native, first found in North America in the late 1980s and since dispersed across much of the United States inadvertently by the sale and exchange of infested plants. The mealybug is usually not noticed until the population on an individual grass plant increases to high levels, at which time superficial symptoms become apparent. Up to 3/16 inch (4 mm) long, the mealybug lives in the tight space between the stem and the enclosing leaf sheath. Colonies are usually established first toward the base (crown) of the plant and spread upward as their numbers increase. The mealybugs themselves are difficult to see until they reach mature adult size. The best way to confirm their presence is to pull a lower leaf sheath away from the stem of an infested plant and look for the white-powdery wax and syrupy honeydew that is produced by and obscures the mealybugs.

A general stunting of growth and an uncharacteristic twisting in the flower heads of grasses are usually the first superficial symptoms of miscanthus mealybug. The stem and sheath tissue often turn dark red in areas where the mealybugs are feeding, especially in late season. Severely infested plants are not killed but are reduced to unsightly, misshapen masses with white powder covering the stems, especially in the lower portion. Affected plants often fail to bloom or the flower stalks may be stunted, causing the inflorescences to open down among the foliage.

Foliar rust on the underside of a leaf of Molinia caerulea subsp. arundinacea in mid August in England.

Foliar rust on the underside of a leaf of Molinia caerulea subsp. arundinacea in mid August in England.

Miscanthus mealybugs live between the stem and the enclosing leaf sheath, and cause condensed and distorted growth.

Miscanthus mealybugs live between the stem and the enclosing leaf sheath, and cause condensed and distorted growth.

No natural predators that might serve as control agents have been found. Topical sprays are ineffective at eradicating the miscanthus mealybug, since they do not adequately penetrate the protected crevices between sheath and stem. Mealybugs can overwinter deep in the crown, so removing top growth only is not effective. A highly toxic but effective control is to lift and divide plants and drench material with an organophosphate insecticide, but this is safe only under professionally controlled conditions and is not appropriate for private residential gardeners. The most environmentally sound approach is to discard and incinerate infested plants, and to inspect any new Miscanthus acquisitions carefully.

Miscanthus blight is a foliar disease caused by Stagonospora and Leptosphae-ria fungi that sometimes affects Miscanthus species. On mature plants, the blight is characterized by reddish brown spots or oval streaks on leaves and leaf sheaths. New leaf margins, tips, and older leaves become discolored and die. The disease can kill young seedlings and newly rooted cuttings. Fungicides can provide effective control.

Deer rarely bother grasses. In fact, they tend to avoid large grasses with sharp-edged leaves, and these can be used effectively to screen and protect other more vulnerable plants and areas.

Rabbits and gophers can be considerable nuisances, devouring and disfiguring or occasionally killing plants. Wire mesh coverings can be used to protect smaller numbers of plants, but this solution is often more unsightly than the problem. It is frequently necessary to protect grasses and sedges only when they are young and their new growth is particularly edible.

Voles sometimes attack grasses from below, eating their roots. In cold climates, vole damage tends to be worst in years with heavy snowfall. The typically random damage voles cause is usually tolerable; however, if a vole population builds to high levels in an extensive groundcover or a grassy meadow landscape, use of toxins and or traps may be the only effective option.

Acquiring Grasses

A quick Web search for “grass nursery” will demonstrate the phenomenal growth in recent years among nurseries producing grasses of all sorts and sizes. Commercial nurseries are now almost exclusively devoted to the container production of grasses, an efficient system offering convenient handling for both producer and consumer. Partly because of this, an impressive array of grasses is now commonly available at retail nurseries, garden centers, and mail-order establishments. Less-common grasses and large quantities of grasses are offered by specialty grass nurseries, often only by wholesale firms catering to professionals.

Miscanthus blight is a fungal disease that causes reddish brown spots or streaks on leaves and leaf sheaths. Photo by Nichole O'Neill.

Miscanthus blight is a fungal disease that causes reddish brown spots or streaks on leaves and leaf sheaths. Photo by Nichole O’Neill.

The roots of this clump of Panicum amarum have been eaten away just below the surface by voles. The grass survived after being divided and replanted.

The roots of this clump of Panicum amarum have been eaten away just below the surface by voles. The grass survived after being divided and replanted.

Whether obtained from a local retail garden center or from a mail-order nursery, container-grown grasses are often best purchased in spring, even though spring buying means acquiring plants long before they’ve reached peak attractiveness. This is especially true for deciduous grasses, which may be just putting on new growth following dormancy. It is never ideal to purchase grasses when they are in full flower since their energy resources are relatively depleted. Nurseries are increasingly offering container grasses in larger sizes intended for immediate impact. This is usually a very viable option; however, it is important to ensure that the plants are not pot bound. The rapid-growing roots of grasses can quickly become congested and compacted in containers, and such plants may be difficult to establish in the landscape. Sufficiently cold-hardy plants grown in containers large enough for healthy root growth may also be acquired and planted in autumn.

Grass plugs (very small grass plants produced in flats) are usually only available to wholesale buyers. Plugs are often transplanted to larger pots and grown to normal retail size; however, they are frequently the most cost-efficient method of establishing large plantings that cannot be done by seeding.

Seed is often the least expensive way to acquire grasses and is sometimes the only way to obtain certain species. Many nurseries offer seed by mailorder. Collecting your own seed, legally and with appropriate permission, can be the best way to procure grasses of local provenance. For gardeners with a keen eye, starting grasses from seed affords the opportunity to watch for interesting variation and to make new selections. If your interest is in cultivated varieties, keep in mind that while some may be suitable for seed propagation, the majority are clonal cultivars that must be reproduced vegetatively to retain their distinguishing characteristics.

Production of landscape-sized container grasses at Pleasant Run Nursery in Allentown, New Jersey.

Production of landscape-sized container grasses at Pleasant Run Nursery in Allentown, New Jersey.

Container production of grasses and sedges at Native Sons, a wholesale nursery in Arroyo Grande, California, specializing in grasses and other plants suited to the state's Mediterranean-type climate.

Container production of grasses and sedges at Native Sons, a wholesale nursery in Arroyo Grande, California, specializing in grasses and other plants suited to the state’s Mediterranean-type climate.  

Plugs of split-beard bluestem, An-dropogon ternarius, produced by North Creek Nurseries in Landenberg, Pennsylvania.

Plugs of split-beard bluestem, An-dropogon ternarius, produced by North Creek Nurseries in Landenberg, Pennsylvania.


Switchgrass, Panicum virgatum 'Cloud Nine', was planted in spring in one-gallon (ca. 4-liter) size in this highway median planting in southern Delaware. A light layer of organic mulch combined with spot applications of broad-leaved herbicide was used to control weeds until the grasses provided complete cover.

Switchgrass, Panicum virgatum ‘Cloud Nine’, was planted in spring in one-gallon (ca. 4-liter) size in this highway median planting in southern Delaware. A light layer of organic mulch combined with spot applications of broad-leaved herbicide was used to control weeds until the grasses provided complete cover.

The same planting in September of the following year.

The same planting in September of the following year.

Planting, Mulching, and Weeding

For the most part, planting grasses is just like planting other garden perennials. The root systems of container-grown plants should be loosened up before planting, and grasses should be thoroughly watered when planted and until they become established. To get the most from the water-conserving nature of grasses, it is best to plant young plants that will most quickly grow beyond the need for supplemental irrigation.

Grasses are sensitive to soil level, especially when young. Ideally, the crown of the grass should sit just at or, if mulch will be used, slightly above the soil surface. Planting too low can cause grasses to rot, and planting too high can cause them to dry out and die. In cold-temperate climates, small container-grown plants and plugs of warm-season grasses should be planted in spring or early summer so that their roots can grow sufficiently to prevent frost heaving during their first winter.

Many grasses can be readily established from seed, and this is often the only practical method for the largest landscapes. Seed may be broadcast dry, hydro-seeded, or planted with a commercial drill-seeder. Cool-season grasses will germinate quickly in spring or autumn. Warm-season grasses seeded in fall may be washed away by rains before they have a chance to germinate, so spring planting is usually preferable. Warm-season grasses including many tallgrass prairie species require cold treatment for germination.

In native habitats, grasses are often observed germinating and growing in exposed soils; however, in gardens and other designed landscapes some type of mulch is usually desirable to help control weeds and conserve moisture.

A tractor-drawn Trux drill seeder was used for this multi-acre planting of Indian grass, Sorghastrum nutans, in northern Delaware. Shown in mid August, these seedlings germinated in spring.

A tractor-drawn Trux drill seeder was used for this multi-acre planting of Indian grass, Sorghastrum nutans, in northern Delaware. Shown in mid August, these seedlings germinated in spring.

Nassella trichotoma at the Royal Horticultural Society's garden, Wisley, grows in light brown gravel mulch which is topped with a covering of larger stones in the adjacent planting of Agapanthus.  

Nassella trichotoma at the Royal Horticultural Society’s garden, Wisley, grows in light brown gravel mulch which is topped with a covering of larger stones in the adjacent planting of Agapanthus.

Although organic mulches such as shredded bark or licorice root are popular choices, it is important not to allow mulch to build up around the crowns of many grasses since this can promote fungal diseases. Organic mulching is most helpful to moisture-loving species including many of the sedges and wood rushes. Many grasses, especially desert and arid-region species, do as well or better when inorganic mulches such as gravel or stone are used, since these conserve moisture and can keep the soil surface cooler than dark-colored mulches.

Young grass plants can be difficult to tell apart. Until you learn to recognize grasses reliably from their vegetative characters, it is best to label plants or to make planting charts to record identities.

Keeping grass plantings free of weeds can be uniquely perplexing since the weeds are often unwanted grasses that can be difficult to distinguish from small plants of desired species. This is especially true when grasses are not in flower. Be diligent about removing weedy grasses at least until newly planted grasses are large enough to identify. When attempting to distinguish weed grasses on the basis of vegetative characters, look for differences in their lig-ules, leaf color, width, and general roughness, smoothness, or hairiness.

Unwanted seedlings of other grasses will sometimes germinate inside a mature clump. These should be pulled out by hand as soon as they are noticed. It is easiest to do this when the soil is wet. If neglected for too long, weed seedlings can be impossible to remove unless the entire plant is lifted and divided. Broad-leaved herbicides may be used around grasses; however, herbicides intended for weed grasses are often effective at eradicating ornamental species.

Cutting Back and Burning

Most grasses require little maintenance other than being cut back once yearly, and even this is done more for neatness than for the needs of the grass. The general rule in cold-temperate climates is to cut back grasses in late winter or early spring before new growth begins. Grasses left standing through the cold season do much to keep the landscape alive and dynamic. They respond to winter winds; glow in the winter sun; provide exquisite frameworks for frosts, ice, and snow; and provide important shelter for wildlife.

Smaller grasses and small numbers of larger grasses may be easily trimmed back with hand pruners or shears. Gloves should always be worn to protect against cuts. Some grasses such as miscanthus have sharp leaf margins that can cause cuts to unprotected hands and face. Electric hedge shears can make quick work of cutting back both large grasses and groundcover plantings of smaller species. Power string trimmers and blade trimmers are quick but cause messy shattering that may require tedious clean-up.

Many evergreen grasses and sedges do not need to be cut back yearly and may grow attractively for a number of years with just minor grooming. Old growth or discolored foliage is often easily removed by gently combing plants by hand.

Though grasses in natural habitats grow without anyone to cut them back, fires have frequently served as renewing forces. The benefit of controlled burning of prairie restorations and large grassy meadow plantings is well established. The crowns and deep root systems of grasses are undamaged by fire, unlike many weedy herbaceous and woody species, and the nutrients returned to the soil by burning are often beneficial to grasses. Burning grasses, however, is a potentially dangerous activity best undertaken by professionals with organized safety support. Parks, conservation agencies, and public gardens that practice controlled burning typically have fire departments on site.

Three photographs show the same planting of prairie dropseed, Spo-robolus heterolepis, in the author’s Pennsylvania garden from snowy mid winter through mid spring.

Even smaller grasses such as this prairie dropseed contribute winter interest if left standing

Even smaller grasses such as this prairie dropseed contribute winter interest if left standing

Hand pruners are used to cut back old growth in late March.

Hand pruners are used to cut back old growth in late March.

New growth is a soft bright green in late April.

New growth is a soft bright green in late April.

Hand shears are used to cut back coastal switchgrass, Panicum amarum, to approximately 5 inches (13 cm) in early spring.

Hand shears are used to cut back coastal switchgrass, Panicum amarum, to approximately 5 inches (13 cm) in early spring.

Evergreen and semiever-green sedges do not require annual cutting back, and some species may be damaged by it. If plants require grooming, it's often best to use fingers to gently comb out old foliage, as is being done here with Carex appalachica and C. albicans.

Evergreen and semiever-green sedges do not require annual cutting back, and some species may be damaged by it. If plants require grooming, it’s often best to use fingers to gently comb out old foliage, as is being done here with Carex appalachica and C. albicans.

The Louisville (Kentucky) Fire Department is close at hand for this controlled burn of Iroquois Park's Summit Field grasses by the Louisville Olmsted Parks Conservancy and Metro Parks.

The Louisville (Kentucky) Fire Department is close at hand for this controlled burn of Iroquois Park’s Summit Field grasses by the Louisville Olmsted Parks Conservancy and Metro Parks.

Cut flowers and foliage of grasses, both fresh and dry, can be enjoyed indoors at almost any time of year. Cut from the author's garden, this late-October dining room table arrangement features wild-oat, Chasmanthium latifolium, with cut-leaf sumac, threadleaf bluestar, and heart-leaved aster

Cut flowers and foliage of grasses, both fresh and dry, can be enjoyed indoors at almost any time of year. Cut from the author’s garden, this late-October dining room table arrangement features wild-oat, Chasmanthium latifolium, with cut-leaf sumac, threadleaf bluestar, and heart-leaved aster

Small-scale controlled burning of grasses in residential gardens may be practical if necessary precautions are taken and local burning ordinances permit such activity. Many grasses, especially miscanthus, burn with surprising intensity. Choose a calm day in late winter or early spring, and keep a watering hose within reach. Ensure that children and pets are at a safe distance, and check grasses for active bird nests and beneficial insect egg cases. Do not attempt to burn grasses if they are close to shrubs or trees, especially conifers. I once photographed 60-foot (18-m) tall spruces in a private garden that had been reduced to brown needles and smoldering cinders by the uncontrolled burning of grasses at their feet.

Propagating, Dividing, and Transplanting

One approach to propagating perennial grasses is to sow seeds in pots or flats in a cold frame or greenhouse and then transplant young seedlings into the landscape. In cold-temperate climates, the majority may be sown in late winter or early spring and planted out after they reach a few inches in height, once the danger of killing frosts is past. Germination rates vary widely. Some grasses will germinate in a few days, others will take weeks or months, and certain species require periods of cold before they will become capable of germination. Seed propagation is a useful way of ensuring genetic diversity in plantings.

Division is the usual means of vegetatively propagating grasses and is typically done when they are in active growth, although many grasses including warm-season North American prairie species will tolerate dormant division. Some grasses may also be rooted from stem cuttings or produced by tissue culturing.

Enhancing Delaware Highways team member Gary Schwetz collects seed from a Delaware population of Indian grass, Sorghastrum nutans, to be used to extend a naturally occurring population of this grass on a roadside landscape. Propagation by seed of known origin is one way of continuing local genetic diversity.

Enhancing Delaware Highways team member Gary Schwetz collects seed from a Delaware population of Indian grass, Sorghastrum nutans, to be used to extend a naturally occurring population of this grass on a roadside landscape. Propagation by seed of known origin is one way of continuing local genetic diversity.

This older clump of miscanthus is dead in the center and is ripe for renewal by divisions taken from the outer ring of healthy tissue.

This older clump of miscanthus is dead in the center and is ripe for renewal by divisions taken from the outer ring of healthy tissue.

Smaller grasses such as this tufted hair grass, Deschampsia cespitosa, can be lifted and then divided with a knife. The fibrous root systems of grasses can be exposed for brief periods but should never be allowed to dry out.

Smaller grasses such as this tufted hair grass, Deschampsia cespitosa, can be lifted and then divided with a knife. The fibrous root systems of grasses can be exposed for brief periods but should never be allowed to dry out.

Relatively few ornamental grasses have been patented or trademarked; however, these practices are increasing. Patented grasses may not legally be propagated for sale unless licensed by the patent holder. Trademarks (usually indicated by ™ or ®) do not exclude others from propagating plants, but restrict the commercial use of the trademark to the legal holder of the mark or others licensed by the holder.

As grasses age, their clumps tend to die in the center, and this often results in plants that are weak and floppy. Such plants can usually be renewed by division and transplanting. For small and medium-sized grasses, it is best to lift clumps from the ground with a strong trowel or sharp spade and then use a knife to divide them. Discard dead material from the center, and replant healthy live divisions from the outside of the clump. Divisions should be thoroughly watered immediately following replanting. Running grasses can also be divided if care is taken to secure sufficient roots with each division.

A sharp sturdy spade, not a shovel, is absolutely essential for dividing and managing large grasses. Mature specimens are often too big and heavy to be lifted in one piece, and must be sectioned in the ground with a spade before they can be lifted. Unless you are working around buried electrical lines, the best type of spade is one constructed entirely of modern steel alloys, which are light but exceptionally strong. Some manufacturers offer spades with cushioning rubber footpads at the top of the blade. This type of tool is comfortable to use when cutting into the roots of grasses and is strong enough to be used to lever heavy divisions out of the ground.

A strong but light alloy spade with rubber cushions is used to make two divisions from a healthy clump of coastal switchgrass, Pani-cum amarum, in early spring. With larger grasses, it is often easiest to use the spade to divide the plant while in the ground and then lift each division.

A strong but light alloy spade with rubber cushions is used to make two divisions from a healthy clump of coastal switchgrass, Pani-cum amarum, in early spring. With larger grasses, it is often easiest to use the spade to divide the plant while in the ground and then lift each division.

A strong but light alloy spade with rubber cushions is used to make two divisions from a healthy clump of coastal switchgrass, Pani-cum amarum, in early spring. With larger grasses, it is often easiest to use the spade to divide the plant while in the ground and then lift each division. A strong but light alloy spade with rubber cushions is used to make two divisions from a healthy clump of coastal switchgrass, Pani-cum amarum, in early spring. With larger grasses, it is often easiest to use the spade to divide the plant while in the ground and then lift each division.

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