Mulches are either organic or inorganic material placed on the soil around the vegetable plants. Mulches can perform a number of useful functions. They protect against soil erosion by breaking the force of heavy rains; they help prevent soil compaction; they discourage the growth of weeds; they reduce certain disease problems. Organic mulches improve the soil texture. Mulches are also insulators, making it possible to keep the soil warmer during cool weather and cooler during warm weather.
Mulches do not eliminate weeds. They can, however, help control them if the area has been cleared of weeds to begin with. If the mulch is thick enough, the weeds that are already growing won’t be able to push through, and the darkness will frustrate the germination of others. Persistent weeds can push their way through most mulch, but if they’re cut off at the soil level a few times they’ll die. Sometimes mulches can improve the appearance of the vegetable garden by giving it a neater, more finished look. Some mulches give the area a professional look that only a true vegetable gardener can appreciate.
Whether you use an organic or an inorganic mulch, take care not to put it down before the soil has warmed up in the spring—the mulch will prevent the soil from warming and slow down root development. In the average garden in a cool-season climate mulch should be applied about five weeks after the average date of last frost.
Organic mulches improve soil quality
Organic mulches are organic materials that, when laid on the soil, decompose to feed the microorganisms and improve the quality of the soil. If you see that the mulch you’ve put down is decomposing quickly, add nitrogen to make up for nitrogen used by the bacteria. Some mulches can carry weed seeds; others can harbor undesirable organisms or pests, but both diseases and pests can usually be controlled by keeping the mulch stirred up. When you’re cultivating, lift the mulch a little to keep the air circulating.
To use an organic mulch, spread a layer of the material you’re using on the surface of the ground around the plants after the soil has warmed up in spring; the plants should be about four inches tall so the mulch doesn’t overwhelm them. If you’re using a fluffy material with large particles, like bark chips, make the layer about four inches thick. If you’re using a denser material like straw or lawn clippings, a two-inch layer will be enough. Be careful not to suffocate the vegetables while you’re trying to frustrate the weeds.
The following are organic materials commonly used as mulches:
Buckwheat hulls.
These hulls last a long time and have a neutral color, but they’re lightweight and can blow away; and sometimes they smell when the weather is hot and wet.
Chunk bark.
Redwood and fir barks are available in several sizes. Bark makes good-looking paths and gives the area a neat, finished appearance, but it’s too chunky to be the ideal mulch for vegetables. It also tends to float away when watered or rained on.
Compost.
Partly decomposed compost makes a great mulch and soil conditioner. It looks a little rough, but other gardeners will know you’re giving your garden the very best.
Crushed corncobs.
Crushed cobs make an excellent and usually inexpensive mulch. The cobs need additional nitrogen, unless they are partially decomposed. Sometimes corn kernels are mixed in with the crushed corncobs; this will create extra weeding later on.
Lawn clippings
Do not use clippings from a lawn that has been treated with a herbicide or weed killer—these substances can kill the vegetables you’re trying to grow. Let untreated clippings dry before putting them around your garden; fresh grass mats down and smells bad while it’s decomposing.
Leaves.
Leaves are cheap and usually easy to find, but they blow around and are hard to keep in place. They will stay where you want them better if they’re ground up or partially decomposed. Nitrogen should be added to a leaf mulch. Do not use walnut leaves; they contain iodine, which is a growth retardant.
Manure
Vintage, partially decomposed manure makes an excellent mulch. Manure has a strong bouquet that you may not appreciate, but don’t use a manure that has been treated with odor-reducing chemicals; treated manures contain substances, such as boron, which are unhealthy for plants. Never use fresh, unrotted manure, it can kill your plants.
Mushroom compost
(leftover, used). Where it’s available, used mushroom compost is generally inexpensive. Its rich color blends in well with the colors of your garden.
Peat moss.
Peat moss is expensive when large areas have to be covered. It must be kept moist or it will act like a blotter and pull moisture out of the soil and away from the plants. Once it dries, peat tends to shed water rather than letting it soak in, and the fine grades of peat have a tendency to blow away.
Poultry manure.
This is potent stuff—poultry manure is about twice as strong as cow manure; proceed with caution. A good, weathered, four-year-old poultry litter can give you mulch, compost, and high-nitrogen fertilizer, all at the same time.
Sawdust.
Sawdust is often available for the asking.
but it needs added nitrogen to prevent microorganisms from depleting the soil’s nitrogen.
Straw.
Straw is very messy and hard to apply in a small area, and it’s highly flammable—matches or cigarettes can result in short-order cooking. It does, however, look very professional.
Wood chips or shavings. More chips and shavings are available now that they are no longer being burned as a waste product. They decompose slowly and add needed nitrogen. Beware of maple chips, which may carry verticillium wilt into your garden.
Recycle rugs, papers as inorganic mulch
Unlikely though it may seem to the inexperienced gardener, the following materials can be used effectively as inorganic mulches.
Aluminum foil. Foil is expensive if you’re dealing with more than a small area, but it does make an effective mulch. It reflects sunlight, keeps the plants clean, and scares birds away from your garden.
Backless indoor-outdoor carpet. Indoor-outdoor carpeting is ideal for the small garden and makes it easy for the fastidious gardener to keep the place neat. Water goes through it easily, and the weeds are kept down.
Newspapers. Spread a thick layer of newspapers around the plants. Keep them in place with rocks or soil. They will decompose slowly and can be turned under as a soil modifier.
Rag rugs. An old rag rug holds water and keeps the soil moist. It won’t look as neat as backless carpeting, but it will be just as effective.
Plastic mulches: pros and cons
Both clear and black polyethylene are used by commercial growers as inorganic mulches. Clear plastic is not recommended for small gardens because it encourages weeds; weeds just love the cozy greenhouse effect it creates. Black plastic is sometimes used in small gardens for plants that are grown in a group or hill, such as cucumbers, squash,orpumpkins. Black plastic should not be used for crops that need a cool growing season— cabbage or cauliflower, for instance—unless it’s covered with a thick layer of light-reflecting material, such as sawdust.
There are some advantages to growing with a black plastic mulch. Black plastic reduces the loss of soil moisture, raises the soil temperature, and speeds up crop maturity. Weeds are discouraged, because the black plastic cuts out their light supply, so you won’t have to cultivate as much; that means less danger of root damage. The plastic also helps
keep plants cleaner. And when you’re making a new garden in an area where there was a lot of grass—if you’ve dug up a lawn, for instance—black plastic can keep the grass from coming back .
There are some disadvantages to keep in mind as well, and one of them is that you may need to water more frequently. Because of their greater growth under plastic, the plants lose more water through transpiration, especially in well-drained, sandy soils. However, you will need to water less if you use black plastic on soil that holds water or drains poorly. If you’re using a black plastic mulch, keep in mind that plants can wilt and rot if the soil moisture is kept at too high a level and there isn’t enough air in the soil.
You can buy black plastic from many garden centers or order it by mail from seed and garden equipment catalogs. It should be at least 11/2 mil thick and about three to four feet wide. If you have a piece of wider or thicker black plastic, use it. The wider plastic is harder to handle, and the thicker type is more expensive, but it works well.
Put down black plastic mulch before the plants are set out. Try to pick a calm day; a strong wind will whip the plastic about and make laying it down hard work. Take a hoe and make a three-inch deep trench the length of the row. Lay one edge of the plastic in the trench and cover the edge with soil. Smooth the plastic over the bed and repeat the process on the other side. Be sure the plastic is anchored securely, or the wind will get under it and pull it up.
When you’re ready to plant, cut holes about three inches across for the plants or seeds. After planting, anchor the edges of the holes with stones or soil. Water the plants through the holes in the mulch. After a rain, check to see if there are any spots where water is standing. If there are, punch holes through the plastic so the water can run through. After the plants are harvested, the plastic can be swept off, rolled up, and stored for use the next year.
