Plant Selection, Installation, and Management to Affect Groundwater - Introduction to Phytoremediation of Contaminated Groundwater - page 169

stored water, so plastic wrap should be used and the cuttings
set in buckets of water during storage (Fig. 7.3 ).
In general, the type of plant installation method will be
based on the type of plant, or its stage of growth, to be
installed. As stated previously, perhaps the most commonly
installed plant at phytoremediation sites is the hybrid poplar
tree. It can be obtained as a cutting of various sizes from 6 in.
(15 cm) to 10 ft (3 m) with no roots, a rooted cutting, a
bagged-and-wrapped root ball, or as a full-grown specimen
in a multi-gallon container. It should not be surprising,
therefore, that there are many different ways to install even
the same type of plant. Regardless of plant size, the larger
the hole that a plant is introduced into, the better as far as the
life of the plant is concerned.
Common to all planting methods, planting can commence
any time after the soil temperature has reached at least 50 F
and the threat of frost has passed. This is to ensure that the
soil temperatures can support root respiration and growth. In
general, at least one-third of the bare-root cutting should be
installed below ground (2 ft (0.6 m) for a 6-ft (1.8 m) cutting,
for example), and for whips at least one-half, if not more,
below ground. At least one lateral bud should remain above
ground and in the right direction (facing upwards!). This is to
ensure that one main stem grows upward, rather than having
multiple, but weaker, stems.
If the stock is wide enough in diameter (0.5-2 in.
[1.2-5 cm]) and at least 2-3 ft (0.6-0.9 m) long, the cuttings
can be driven into the ground with a rubber mallet if the soil
is soft enough and the soil chemistry is conducive to growth

without amendment. For shorter cuttings, say less than 24 in.
(60 cm) for example, site installation can be as simple as
using a short piece of reinforcing bar (rebar) and a sledge
hammer to create a small-diameter hole in which the cutting
can be inserted. This technique works well in loose sandy
soils or topsoil fill material but may not ensure cutting
survival if the sediments are tight (clays and silt) or
contaminated, as new and adventitious roots will be in con-
tact immediately with the contaminated soil. If preliminary
data indicate contamination in the soils to be planted and it is
cost prohibitive to remove this and add fresh backfill, then a
large-diameter auger hole filled with fresh uncontaminated
loam would be better (Cook et al. 2010).
Large vegetative cuttings that exceed 6.5 ft (2 m), called
whips or poles, can be planted in boreholes drilled or
trenches installed with the appropriate equipment. This
approach of using longer stock is used at sites where the
depth to water table is greater than 15 ft. Holes also can be
made manually with a post-hole digger or a 1- to 2-person
rotary auger. The latter is a more rapid method to install a
relatively low number of cuttings at smaller sites. Larger
sites where even small cuttings will be planted do better with
a more automated hole-creation method. A tractor with the
appropriate front-loader or 3-point attachment can be used to
rapidly create holes for planting using a rotary auger (Cook
et al. 2010: Fig. 7.4 ).
As cuttings emerge from dormancy, leaves develop from
the bud scales. This 'growth' actually is enlargement of the
previously developed leaves with water. Water should be

Fig. 7.4 Drilling boreholes
using rotary augers prior to
planting hybrid poplar cuttings,
Elizabeth City, NC, United States
Coast Guard Support Center
(Photograph by author; see Cook
et al. 2010 for further
explanation).