Trees, Shrubs, and Vines
Woody plants are a permanent, year-long presence in the landscape. This permanence helps determine their major uses.
Consider the landscape as if it were a living room. The floor would be formed by low-growing plants and ground-hugging constructions, like lawns and ground covers, patios and pavement. They form the base of any landscape. But what about the rest of the landscape, the walls and ceiling? That’s where trees, shrubs, and climbing plants come in.
Shrubs and vines, as well as related constructions such as fences, form the walls of the room. They help define its boundaries, separating your yard from your neighbor’s and one garden area from another. This is most obvious when plants are grown as a hedge, but even informal plantings of shrubs will help define bounds between various areas.
A simple cluster of shrubs, for example, can separate the children’s play area from a quiet rest area or the service area with its shed, garbage cans, and clothesline. Formal hedges, because of the obvious barrier they create, are most often used to define property lines.
Shrubs can also offer a screen for privacy, or they can block unsightly views. Deciduous shrubs are good choices for screening: They offer privacy during the summer months yet allow a maximum amount of winter sunlight to penetrate your yard at a season when light is at a premium. If the goal of the screen is to block an undesirable view, evergreens — both conifers and broad-leaf — are the plants of choice, since their cover is permanent. Taller shrubs can also be used as windbreaks or to create a bit of shade in an overly sunny spot.
Vines are used much like shrubs, except they must grow on some sort of support, such as a fence or trellis. A hedge may need many years to grow high enough to block a view. You can create the same effect in a year or two by planting a vining plant at the base of a fence. If you can’t put up an attractive fence, a simple chain-link one with vines planted at the base will offer security without being obtrusive.
Vines are also useful in places where space is lacking. Most shrubs quickly attain a diameter of three to five feet; this can seem a waste of space in a tiny urban yard. Vines grow vertically: Most cling so closely to their support that they take up only inches of horizontal space.
For security purposes, you might want your wall to be composed of plants with spiny leaves or branches. A fire thorn or barberry hedge, for example, can be as effective a barrier as a chain-link fence but far more attractive.
After the “floor” and “walls” have been taken care of, the outdoor living room needs a ceiling. Although the sky can serve as an outdoor ceiling, it can be too much of a good thing. The vastness of the sky keeps a garden from feeling intimate.
Trees block out part of the sky, defining the sky’s borders. Trees also contribute structure to the garden. Trunks and branches act as posts and beams to bring the sky down to a more human scale. For this management of the sky, trees have a purpose in every landscape, even the smallest one.
Trees have other uses as well. No other characteristic of trees is as obvious in the landscape as the shade they provide. Through their ability to filter sunlight and to cool the air through evapotranspiration, leaves can reduce the temperature by up to 10 degrees Fahrenheit on a hot summer day. Shade also protects from excess sun that can annoy your eyes and be dangerous for the skin. So every garden should have at least one shady nook. Some trees are known as “shade trees.” These are usually taller trees with a broad crown. Smaller trees can also provide plentiful shade, although you may prefer to remove some of the lower branches for sitting.
Putting It all Together
With the structure of your “living room” — floor, walls, and outdoor ceiling — now clearly defined by the lawns and woody plants it contains, you have the base on which to build your landscape. All you have left to add is the “furniture”: flower beds, accent plants, and the like.
Defining Woody Plants
Woody plants come in all shapes and sizes, from tall and upright to low and creeping. Aside from producing wood, these plants have one thing in common: persistent stems, meaning the stems survive from one year to the next. This distinguishes woody plants from herbaceous (nonwoody) plants like perennials, which die back to the ground each year. Although many woody plants lose their leaves in the winter or dry season, the stems survive and produce new leaves the following year. Trees, shrubs, and most vines are woody plants, but the boundaries between each group are not always clear.
Trees Versus Shrubs
Although most people recognize a tree when they see one, defining what does and does not constitute a tree is not easy. This is particularly the case when distinguishing between a tall shrub and a small tree.
One common definition of a tree is a perennial plant that bears only one single woody stem (the trunk) at ground level. Size is not a determining factor in this definition. A tree can reach 100 feet or more in height or only one foot for miniatures. In practice, however, a very small tree is likely to be treated as a shrub. Woody shrubs have several stems rising from ground level. Shrubs are also usually smaller, often 3 to 12 feet tall. There are many obvious exceptions, such as trees with multiple trunks that can be very hard to distinguish from tall shrubs. Other plants can be either trees or shrubs depending on how they are grown. These general definitions, however, do help to distinguish between the two groups.
Humans also influence plant growth by pruning and other practices. For example, a gardener may prune off all the secondary stems of a shrub, leaving one to three main trunks, thus creating a “standard” (tree-form shrub). A gardener may also repeatedly cut back young trees, forcing them to branch at their base, turning them into shrubs. Nature does the same thing. Some plants that normally grow as trees will take on a shrub form at the northern limits of their range. Each winter their top growth is pruned back by cold, causing them to develop multiple branches rather than a main trunk. Subshrubs are plants with woody stems, yet they die back at least part way to their roots each year. Subshrubs are usually treated as perennials. Some true shrubs, such as butterfly bush, will behave as subshrubs in cold or extreme climates.
Vines can be separated into three main categories: woody vines, with permanent above-ground stems; perennial vines, which die back to the ground each winter and then sprout again in spring; and annual vines, which start anew from seed each year. A woody vine can be considered a shrub that needs some sort of support to grow well. Some woody vine (including many types of clematis) die back to the ground each year, just as subshrubs do, especially under harsh climatic conditions. Only woody vines are covered in this section.
Deciduous or Evergreen?
Trees, shrubs, and woody vine are classified as either deciduous or evergreen. Deciduous woody plants usually lose their leaves in the fall. In warmer climates leaf loss can occur at other times in the year, notably at the onset of the dry season. Evergreen plants remain clothed in foliage throughout the year. They do lose their leaves, but gradually rather than all at once; they are never completely barren. Some woody plants are classified as semievergreens. Their leaves are persistent in most conditions but fall off in harsh ones, especially in cold or very dry climates. Deciduous plants often have attractive fall colors. Evergreens present a continuous display of green foliage, even when deciduous plants are bare.
The term “evergreen” is often mistakenly thought to pertain strictly to conifers (cone-bearing plants). This is not the case. There are broad-leaf evergreens, including boxwoods and most rhododendrons, and deciduous conifers, such as larches and bald cypress. In many plant catalogs, woody plants are divided into three categories as to their foliage: deciduous, broad-leaf evergreens, and needled evergreens.
Source: Curb Appeals Blog