Horticulture Principles and Practices

The pruning of ground covers may be necessary after years of growing under
favorable conditions. Under such conditions, growth must be controlled by pruning
shrubby species such as junipers and vines such as English ivy (Hedera helix) in early
spring. Pruning reduces overcrowding, which causes undesirable competition among
plants and subsequent loss of vigor. Renewal pruning, which helps to rejuvenate the
ground cover, may be accomplished by mowing vines with a trimmer.
Ground covers may be attacked by spider mites, Japanese and other beetles, caterpillars,
powdery mildew, aphids, and other pests. However, diseases and insects are usually
not a problem for ground covers in the landscape. When conifers are grown by the
roadside in cold climates, the salts used on icy roads in winter may damage the needles.
If the ground cover is not uniform (empty spots occur), the spaces can be filled by
vegetatively propagating the species using applicable methods. For example, creeping
junipers (Juniperus horizontalis) can be layered, and moss phlox (Phlox subulata) can
be propagated by cuttings.
522 Chapter 17 Installation of the Landscape
17.6 ORNAMENTAL GRASSES
Grass is one of the basic elements in a landscape design. The establishment of a lawn is
discussed in detail in Chapter 18. The discussion in this module is limited to grasses
planted in spots in the landscape for decorative purposes.
Grasses used as ornamentals in the landscape may be grouped into four categories:
true grasses, sedges, rushes, and bamboos, the last three sometimes being described as
grass relatives. They are used in the landscape for the color of their foliage and the variety
in their sizes, shapes, and forms. These plants are easy to grow and care for in the
landscape. They can be grown in beds or in containers. Like ground covers, certain
grasses are clump forming, others form stolons or rhizomes, and some form low mounds
(e.g., fountain grass [Pennisetum alopecuroides]).
17.6.1 CHOOSING GRASSES
As discussed in Chapter 18, turfgrasses may be placed into two general categories: cool
and warm season. Warm-season grasses become dormant in winter and turn brown.
Cool-season grasses tend to be evergreen or semievergreen. The space to be allocated to
the grass must always be considered. Clump-forming species tend to be contained and
less aggressive or invasive. A limited number of species, including blue lyme grass
(Elymus arenarius ‘Glaucus’), are notorious for being very aggressive. When such
species are grown, they may be held in check by planting them next to pavements or
installing edging strips. Apart from climate, soil pH, salinity, and drainage should be
considered in making choices. Table 17–7 presents a list of popular ornamental grasses.
A number of annual grasses can be grown in the garden; they can be cut and dried or used
fresh for cut flowers.
17.6.2 SOIL PREPARATION AND PLANTING
If many grass clumps are to be planted, a bed may be prepared for the purpose. For a few
clumps, the spots for planting should be prepared in the same way as a flower bed. It is critical
that the area be free of weeds. Regular lawn grasses should not be allowed to invade the
space of ornamental grasses since they are difficult to control after the invasion. Aggressive
species such as quack grass (Agropyron repens) and popular lawn grasses such as Bermuda
grass (Cynodon dactylon) should be kept away from ornamental species.
Ornamental grasses should be allocated ample space for growth. Clump-forming
grasses can be assigned space since their adult size is predictable. When planting grasses
for ground cover, spacing should be closer than when planting a few clumps. Grass for
planting may be purchased as container-grown or bare-root plants. Thorough watering
and mulching are needed after planting. Some grasses may be started from seed. Species