Selecting Trees, Shrubs, and Vines for the Landscape
By John Jett, WVU Extension Service horticulture specialist
Woody ornamental plants are key components in a well-designed, useful environment. This large body of plants falls into three groups: trees, shrubs, and vines.
- Trees are woody plants that produce one main trunk and a more or less distinct and elevated head (height of 15 feet or more).
- Shrubs are woody plants that remain quite low and produce shoots or stems from the base and usually not a single trunk (height of 15 feet or less).
- Vines are climbing or crawling woody or semiwoody plants without self-supporting upright stems.
This article describes how to select plants based on their desired uses; environmental factors influencing plant growth; and procedures for planting and caring for woody plants.
Vines in the Landscape
Like shrubs, trees, and groundcovers, vines can be an important element in any garden landscape. Each species and variety possesses distinctive characteristics that make it well-adapted to certain locations in the landscape plan.
In selecting vines, as in selecting trees and shrubs, carefully review the needs of the area and then choose the most suitable plants. Vines can be useful in a variety of sites. Some are valued for the shade they provide when trained over an arbor. Others add interest to a planting when trained against the wall of a building or used to frame a doorway. Some vines are used to relieve the monotony of a large expanse of wall, being trained in a definite pattern, or to completely cover a wall with leafy green. Others can dramatically change a plain fence. Vines can be useful in forming a cascade of bloom on rough, steep banks while holding the soil in place.
Vines also offer diverse visual qualities and are valued for the rich texture of their foliage, their decorative habit of growth, the fragrance of their blooms, or the beauty of their flowers. Some are valued for the graceful tracery of their simple stems or for the beauty of their leaf patterns. For the home gardener, vines offer a rich source of material for creating interesting, exciting, and beautiful plantings.
Vines can be divided into three groups based on their method of climbing.
- Small rootlike holdfasts – Sometimes they are modified tendrils with small circular discs at the tips while others have small rootlets along the stem that firmly attach the vine to either brick or wood. Examples are Boston and English Ivy.
- Tendrils or leaflike appendages – Plants such as like clematis and grape climb by attaching and winding tendrils or leaflike appendages around the object on which they are growing.
- Twining – All vines do not twine in the same direction, yet the method of climbing is not haphazard. The plants of each species invariably twine in one direction, so it is important to start the winding of young vines around their support in the correct direction. Examples of twiners are bittersweet and wisteria. By knowing in advance how each vine climbs, you can provide the proper means of support for the vines you have selected.
The area to be covered should be studied carefully to determine what type of vine should be used. Rate of growth is a critical consideration since some vines exhibit rampant growth and soon can become a nuisance.
Most vines quickly revert to a tangled mass of foliage over the ground if not given the proper means of support and a reasonable amount of care and maintenance. The best type of support is one that provides structural strength and stability but is neat in appearance.
Like most other plants, vines require some maintenance. Pruning is necessary to remove old wood. This may require making several cuts to each stem so they can be untangled. It is often necessary to prune occasionally to keep the plant within bounds and to guide future growth. As with other plants, vines are pruned to produce better bloom.
Vines may develop sparse foliage low on the trellis and develop a mass of foliage at the top. To prevent this, pinch back the terminal growth of the stems as they develop. Pinching forces lower branching and more uniform distribution of foliage on the trellis. Vines growing poorly should be fertilized in early spring or late fall. One cup of a 5-10-5 or similar analysis fertilizer should be worked into the soil around each vine.
Insect and disease control is important. Spraying against insects can be done as part of the general spraying program for the garden.
Trees and Shrubs
Because there are so many woody plants to choose from for landscaping, you must be careful to select those suited to your needs. Your choice should be based on several factors.
The intended purpose should influence your choice of plants having a certain shape, size, or other physical characteristic. Trees are used for shade, ornament, screening, and windbreaks, and to reduce noise. Shrubs are used for screens, barriers, windbreaks, ornament, groundcover, and wildlife shelter. Both trees and shrubs can be selected to provide edible fruit or nuts.
Providing shade usually requires tall, sturdy, long-living species. Density of foliage determines the amount of shading a tree will provide. A Norway maple produces a very dense shade that prevents other plants from growing under it, and a honey locust provides a light partial shade that does not hinder plants growing below it. Deciduous trees should be used to shade south-facing windows in summer, allowing the sun to penetrate in winter.
Screens usually require plants such as evergreens that produce a dense foliage. In addition, windbreaks must be able to survive rigorous climates. Barrier plantings usually require sturdy plants with a dense growth, and possibly thorns or spines.
Ornamental attributes are quite varied. Both trees and shrubs can be selected for flowers or colorful fruit, interesting foliage, fall color, interesting bark, winter colors of foliage or branches, or interesting shapes of the plants themselves.
Consider the size of mature trees and shrubs and where they are to be used. Tall-growing trees, including the American elm, white oak, Sycamore, and tulip tree, are suitable for two-story and larger buildings. They tend to dominate the low flat appearance of – or even hide – one-story buildings. For attractive and proper balance with one-story buildings, trees that do not grow more than about 35 feet are recommended. Shrubs that outgrow their spaces can hide windows, block walkways, or crowd out other plants. Shrubs can sometimes be kept small by pruning, but this requires continued maintenance. Careful consideration of mature sizes will reduce the need for pruning.
Shape is especially important in selecting trees for ornamental and shade purposes. Tall trees with long, spreading, or weeping branches give abundant shade. Small trees and trees of other shapes – including the narrow, columnar Lombardy poplar; the pyramidal evergreens; the clump birch; and the low-growing hawthorn, crab apple, and dogwood – are useful for ornamental purposes but do not give abundant shade.
Environmental conditions should influence plant selection. Size of the planting area is important, as are site characteristics, such as sun or shade, wet or dry, and exposure to winter winds or pollution. Plants should be tolerant of existing conditions and should be hardy in the appropriate climate zone.
Finally, consider how much maintenance the plant will require and any possible disadvantages – including susceptibility to diseases and insect pests; soft or brittle wood that is easily damaged by wind and ice; fruits and seeds that are large, messy, smelly, or otherwise obnoxious; and abundant shedding of twigs and small branches. Examples are the killing of Lombardy poplar by Cytospora canker or by borers, the breaking of Siberian elm branches by wind and ice, and the bad-smelling fruit of the female ginkgo. The mulberry produces fruit that attracts birds, a characteristic that can be undesirable. Since mulberry fruit is soft and decomposes rapidly when ripe, it is messy on walks and attracts flies and other insects.
Transplants can be classified into three classes according to the way they are dug and/or shipped: barerooted plants, balled and burlapped plants (B&B), and container-grown plants.
Bare-rooted plants have had the soil washed or shaken from their roots after digging. Nearly all are deciduous trees or shrubs that are dormant. Most mail-order plants are of this class because plants in soil are too heavy to ship economically. A good many tap-rooted plants, such as nut trees and some fruit and shade trees, are handled this way because they are not amenable to balling and burlapping.
Bare-rooted plants are also those available in nurseries in early spring with their roots wrapped in damp sphagnum and packaged in cardboard or plastic containers. These need special attention because their roots are tightly bunched up in unnatural positions in order to force them into the package. Discard the sphagnum packing and be sure to spread the roots out to a natural position before planting them.
Plants in the bare-rooted class are planted while dormant. Fall planting is well-suited for these plants. Never let the roots dry out. This is perhaps the single most important source of failure in planting bare-rooted plants. Keep roots in water or wrapped in plastic or wet paper until you are ready to place the plant in the hole. Bare-rooted plants may need extra pruning at planting time to repair damaged roots or stems (Figure 18-5).
Balled and Burlapped (B&B)
B&B plants are likely to have been grown in nursery rows for some time and to have been root pruned so the root system within the balls is compact and fibrous. Such plants reestablish themselves rapidly. Balling and burlapping is primarily used for plants that never lose their foliage and thus are not amenable to bare-root treatment. Such plants are broadleaved evergreens like rhododendrons and azaleas and conifers of all types. A number of deciduous trees and shrubs have branching root systems that are easily contained in a soil ball; these also are sold as B&B plants.
Plants in this class are planted almost any time the ground can be worked. If put out in summer, plants will need special attention to keep them adequately watered.
When selecting a balled and burlapped plant, be sure the ball is sound and hasn’t been broken. Avoid plants that feel loose in the soil balls. Be sure the soil ball does not dry out. These plants usually need very little pruning at planting.
Plants grown in the container in which they are sold are becoming increasingly popular in the nursery trade. Their appearance often misleads gardeners into thinking that all they have to do is set the plants into the ground and forget about them. But in fact these plants need the same careful planting and maintenance as others do; proper watering is critical.
This class of plants may have what can be called a container habit. Their roots are contained in a limited space; they are coiled around one another in the container and may fill it tightly. Some of the larger roots may have become coiled around the trunk and begun a process called root strangulation, or girdling root.
To correct container habit, split the lower half of the root system and spread the roots horizontally. This will prune the roots and encourage new lateral growth, prevent girdling root, and raise the lower roots closer to the soil surface. If the root system is a tight tangle, it is important to separate the roots – even prune some off – and spread them outward in the planting hole.
Another disadvantage to container-grown plants is that once they are planted in the landscape, the roots are often slow to break out of the artificial mix into the native soil. Also, the artificial mixes dry out much more rapidly than the surrounding soil, so watering is very important.
When selecting plants, look for a good natural shape, free from thin spots or broken limbs. Make sure the root ball is solid and the bark has no broken places. Avoid container-grown plants with visible roots circling on the surface or coming out of the drainage holes. Plants should be free of any insects or diseases. Generally, the smaller sizes of a plant will cost less and may establish faster. Don’t buy plants so small that they are in danger of being walked on or mowed over. Container-grown plants can be planted whenever balled and burlapped plants are planted – anytime the ground can be worked.