Environmental Engineering Reference
In-Depth Information
form a callous, lumpy white mass that takes the form of a
slender root. These roots have to form to take up water into
the cutting before too much aboveground shoot growth
occurs, because bud break and leaf growth are driven more
by cell elongation through turgor (caused by water uptake)
than by increased cell division. For poplars and willows,
basal parts of 1-year-old plants perhaps are best. The top
and bottom are cut, close to nodes; this is why cuttings made
from these plants often are shipped from suppliers without
tips. Some cuttings arrive straight and are 1-year-old
cuttings; and some arrive with a heel, which is part of a 2-
year-old plant.
The time from taking a cutting and removal to planting
and root formation is characterized by vulnerability; essen-
tially, the cutting is on its own. Cuttings have no roots, but
do have many lateral buds and root initials. One may be
tempted to use a commercially available rooting hormone or
synthetic auxin to encourage the growth of roots at the
bottom of the cutting, especially since one cannot observe
root growth after installation. Too much rooting compound,
however, actually decreases root formation.
Cuttings should be placed in an organic-rich soil that is
well aerated. This is so that the early nitrogen needs of the
cutting can be met and ensures that adequate water infiltra-
tion occurs to supply the expansion and growth of root hairs.
Such organic-rich soil of high porosity also permits oxygen
diffusion to support root respiration; soils of low porosity
result in anoxic conditions and root death. Still, close contact
should remain between the cutting and the soil, because the
root primordia need access to the soil as soon as possible.
The cuttings can be installed as whips or as bare-root
stock. Whips are large cuttings of complete branches, usu-
ally taken during the dormant season, and are stored under
cool, moist conditions. Typically, nursery's or other third-
party suppliers have a field of growing adult plants, and whip
cuttings are taken after the plants go into dormancy follow-
ing leaf drop and cooler temperatures. Cuttings are the most
commonly available and least expensive form of plant prop-
agation and, therefore, the most widely planted type of
woody plant useful for phytoremediation.
Bare-root plants are cuttings that have a suberized root
system. They start out as cuttings by the grower, are placed
in soil, and then removed from the ground and all the soil is
shaken off. This typically is done in the fall during dor-
mancy, and the plants are kept cool and moist while stored.
Advantages of installing bare-root cuttings over cuttings or
balled-and-burlapped trees include the conveyance of extra
stored carbohydrate in the roots to support early growth
needs, and the decreased potential for soil pests to be
transplanted in that little soil is present. On the other hand,
the process of removing the soil from the roots removes the
root hairs, which are the primary entry points for water
absorption, as well as some of the microbial community in
the rhizosphere. The roots of bare-root cuttings are suber-
ized, so bare-root cuttings still need to develop new
root growth and root hairs after
reinstallation at a
phytoremediation site.
Cuttings or bare-root cuttings are living organisms; this
fact can be easy to forget because they can be shipped like
common freight. When the stock arrives or is picked up and
before planting begins, some steps can be taken to ensure
survival of the cuttings. The first is to place the cuttings, tips
up, in about 3 in. of water. This prevents air from entering
the vascular system and causing embolisms and encourages
the development of adventitious roots. Dead or broken parts
should be removed. The plants should not be removed from
either of these treatments until ready for planting. In the
field, the cuttings should be kept away from wind and direct
sunlight. Basically, they should not be allowed to dry out.
After planting, the top terminal bud, if present, can be
removed to induce growth, although most cuttings do not
come with a terminal bud.
In general, plant installation should occur within 1-4 days
after the cuttings arrive from the supplier. If a longer period
of time is required before planting or if other logistical
problems arise that prevent planting, the cuttings should be
placed in cold storage, such as a refrigerated unit. Keep in
mind that this will decrease the humidity of the air around
the cuttings and increase the chance for the cuttings to lose
Fig. 7.3
Hybrid poplar cuttings placed in a bucket of water prior to
planting (the plastic wrap has been removed to expose the cuttings for
viewing). Note the profuse appearance of adventitious roots along the
sides of many of the cuttings (Photograph by author).
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