Horticulture Principles and Practices

they determine the success and survival of the plant at the site; other factors deal with
economics and aesthetics.
1. Site and space. The space available for landscaping determines the size of plants one
can install. At maturity, trees are the largest plants in the landscape and as such need
a relatively large space per plant to grow properly. In certain areas, homeowners are
not allowed to plant any trees at all or only certain ones in front of their houses if the
property is situated next to a street. Further, species such as birch, elm, and
sycamore are adversely affected by street lighting. Other species such as little leaf
linden (Tilia cordata) and pin oak (Quercus palustris) are excellent street plants.
2. Adaptation. Regardless of the attractiveness of a particular tree, if it does not
grow well in the intended environment, one should not purchase it. Some trees
prefer temperate conditions and others tropical. The species should be selected
with the hardiness zone in mind. In terms of adaptation, the most important
environmental factor is temperature. Every so often, unseasonable weather
conditions occur in an area. The winters may be unusually cold or warm,
which may cause damage from winter chilling or prevent blooming. Unless
one is willing to invest in irrigation, the trees selected should be tolerant of
moisture stress, which is prevalent in summer. For example, the weeping
European birch (Betula pendula) is adapted to zone 2, red sunset (Acer
rubrum) to zone 3, redbud (Cercis canadensis) to zone 4, Japanese maple
(Acer palmatum) to zone 5, pecan (Carya illinoinensis) to zone 6, and live oak
(Quercus virginiana) to zone 7.
3. Plant size and characteristics at maturity. Even though tree growth may be
controlled by pruning, it is best to select a tree whose mature characteristics will
not pose maintenance problems. For example, certain trees branch extensively.
If located near the property boundary, its branches may grow over the fence and
into the neighbor’s yard. This overextension could initiate turf wars between
neighbors, especially in the fall season when leaves drop. The flowering
dogwood (Cornus florida) has a horizontal branching pattern, and shademaster
honeylocust (Gleditisa triacanthos) has open branching. Even if one is able to
control the top of the tree by pruning, the roots may spread and damage pipelines,
house foundations, pavements, or drainage systems. Large trees may grow and
touch overhead electrical cables or shade the lawn and thereby suppress grass
growth.
4. Maintenance. Some species are low maintenance, requiring no pruning or other
landscape maintenance practices. Others must be nurtured with care. Deciduous
trees shed their leaves annually, necessitating fall cleanup.
5. Aesthetics. The shape of the canopy, the foliage (e.g., texture, color, and size), and
the general appearance of a tree may be used to create dramatic scenery in the
landscape. The inflorescence of flowering trees can be stunning in beauty and
design. A weeping tree form is always attractive in the landscape; cut leaf weeping
birch (Betula pendula ‘Laciniata’) and weeping European birch (Betula pendula)
both have weeping forms, the former being oval and the latter pyramidal.
6. Seasonal enjoyment. Avid plant lovers look forward to seasonal changes in the plant
cycle and their enjoyment from viewing the changes. The fall colors produced by
trees such as dogwood, oak, ash, aspen, and maple are very impressive. Flowering
plants such as flowering crab apple, magnolia, redbud, and flowering dogwood
produce bursts of very attractive flowers that many look forward to each year.
7. Fragrance. The inflorescence of some plants produce very pleasant fragrances.
A good example is the amur maple (Acer ginnala), with purplish flowers, which
is often used as a specimen plant.
8. Fruiting. Certain trees have the capacity to produce edible fruits (e.g., apple,
cherry, plum, and peach). Other fruiting trees such as mulberry and olive, when
used in the landscape, should be discouraged from flowering because they litter
the ground with many dropped fruits.
17.10 Choosing Trees 525