Selecting Plants for Landscape Design

When selecting plants (or plant materials as they are called in horticultural terms), you need to understand the characteristics of the various plants, the many ways that they can be used in your design, and the types of conditions under which they grow best.

Categories of Woody Plants

There are four main categories of woody ornamental plants. They include trees, shrubs, vines, and ground covers.

Trees typically are 15 feet or higher. They have a main trunk and typically a distinct elevated canopy.

Shrubs are usually 15 feet or shorter. They typically have multiple shoots or stems branching out from their base.

Vines grow horizontally or climb vertically. They can be evergreen or deciduous, woody or herbaceous, annual or perennial. They can be grown for their flowers, fruit, or simply their foliage.

Ground covers are low-growing plants that hug the ground and act like a living mulch. They are densely matted and typically range in height from a few inches to knee high. These can include a wide variety of plant types including but not limited to shrubs, vines, ferns, ornamental grasses, and bamboos.

There are many species of woody plants for use in landscaping. Base your selection on their aesthetics, how they are to be used, and cultural requirements.

Plants Selection Based on Aesthetics

There are several aesthetic design qualities that should be considered when selecting plants for a landscape.

Form

The form or shape of a plant is the first design quality that should be considered when selecting plants. There are many such forms, and they vary based on the type of plant. For example:

Shrubs are round, columnar, upright, or spreading.
Deciduous trees are cone-shaped or pyramidal, erect, columnar, round, weeping, oval, or vase-shaped.
Evergreens are round, narrow pyramidal, broad pyramidal, columnar, spreading, and creeping.

These forms can be irregular or symmetrical. The more irregular or asymmetrical a plant's shape is, the more it draws attention and attracts the eye.

Weeping forms lead the eye downward to the ground while vertical forms lead the eye upward toward the sky, which creates a feeling of height and giving a sense of narrowness to the space. Ascending forms are used for accents, so they should not be used often in a design.

Rounded forms are neutral forms (non-accenting) and the most common form of plants. They encourage easy eye movement around a landscape. This makes them ideal for grouping in mass compositions. Rounded plants can also be used to surround conical, pyramidal, and columnar plants to temper their accenting quality.

Use a mixture of forms instead of plants that all have the same form. The latter leads to a boring design. A mixture of forms will provide variety and interest to your design.

Texture

Texture is the second design quality that should be considered and refers to how thin or dense, coarse or fine, tough or smooth, heavy or light a plant's foliage is. It is useful in creating contrast, but care should be taken not to contrast two extreme textures side by side (e.g. using very coarse plants next to very fine plants).

Instead, use graduated textures in compositions utilizing several plant types from coarse to medium coarse to medium fine to fine. This provides a smooth transition for the viewer's eye as it moves from the coarsest to the finest plants. Each plant in this transition should have a leaf size roughly half that of the preceding coarser plant. And as you move from coarse to less coarse in the transition, each type of plant used should increase in number. For example, if you start with one coarse plant, then you will want to use probably three of the next plant type with leaves roughly half the size of the preceding first coarse plant, seven of the next plant type with even smaller leaves, and maybe 11 of the next plant.

Coarse textures should be used in large areas. If used in small areas, it will make the areas feel smaller than they are and appear harsh to the eye.

Color

Color is the third design quality to consider, and it adds the most to a landscape's appeal. While it evokes the greatest response in people viewing the landscape, it should not be the sole quality on which the design is based.

Yellow, orange, and red are warm colors on the color wheel. These warm colors generally stand out in the landscape, excite the viewer, and evoke feelings of cheerfulness and happiness. They appear to come toward the viewer or pop out of the landscape.

Green, blue, and violate are cool colors on the color wheel. Cool colors tend to blend into the landscape and evoke feelings of calm and rest in the viewer. These colors tend to recede into the landscape and create a perception of being farther away than they are.

Complimentary colors are those directly opposite of each other on the color wheel. They always consist of a warm and a cool color, which creates contrast in color, emotional response, and distance perception. Colors that are side by side are called analogous colors. When used in combination with one another, they are pleasing and balanced.

When selecting plants for a landscape design, do not simply think about the color of their flowers as these are typically only present for short time each year. More emphasis should be placed on the foliage of the trees and shrubs which will appear in the landscape throughout the year. Also, consider how the color of the leaves of deciduous trees and shrubs used in the landscape will appear at various times of the year like fall.

Plant Selection Based on Landscape Uses

Plants can be selected for a landscape based on their intended use or purpose. They can serve a variety of functions like providing shade, screening view, blocking out noise, creating windbreaks, creating ground covers, attracting and/or providing shelter for specific types of wildlife, repelling insects, or providing edible fruit.

Trees and Shrubs in Landscapes

Obviously, if the goal is to provide shade, then tall, strong trees with a very long lifespan are typically required. How dense the foliage is should also be considered as it determines the amount of light that is allowed through. It should be noted that shade trees with dense foliage make it difficult to grow other things (especially grass) below them. Consider also where the shade will be cast at different times of year when placing them.

Plants selected for screening views should have dense foliage. They should typically be evergreens since most homeowners will likely want to screen the view year-round.

Those plants used as barriers to keep people or wildlife out of a yard or garden should typically have strong branches and dense foliage. They may even need to have thorns or spines.

There are many options for ornamental trees and shrubs. They might be selected for the color of their flowers, color of their leaves in fall, color of their fruit, texture of their leaves, overall form or shape of the tree, and more.

Vines in Landscapes

Vines are very useful in landscapes for changing the form of undesirable posts, poles, or trees. Climbing or clinging vines can be used to add interest to boring exterior walls and fences. However, care should be taken when considering vines on walls and fences. They can trap moisture on wooden fences or walls causing them to rot. Clinging vines can loosen mortar between bricks or stones in walls weakening the structure and can be difficult to remove later once they are well established. Vines can also be used as ground cover often in shady spots where other grasses and plants will not grow.

Ground Covers in Landscapes

Ground covers are used in landscape designs for many reasons. They are often used where turf grass will not grow or is not wanted. They can be used as a living mulch to hold moisture in the soil in summer, keep the ground below them warm in winter, and suppress weeds. Ground covers can be used to hide unsightly objects like inground meters or tree roots. They are great on steep hillsides as an alternative to mowing or as an erosion control method.

Plant Selection Based on Cultural Considerations

There are cultural considerations that should be part of your decision-making process when selecting plants for a landscape design.

Hardiness

Select plants that match their growing zones and climate. For example, in regions where freezing temperatures are common, you will want cold hardy plants that can survive the cold.

Soil Conditions and Moisture

Consider the moisture and soil conditions of the environment for which you are designing. Select plants that thrive in that type of environment. For example, some plants grow well in extremely moist or extremely dry soil while others do not.

Maintenance Requirements

It is important to understand your client's financial and physical ability and desire to maintain the various plants that you select. If they do not want to or are incapable of taking care of plants that, for example, are prone to disease and need constant treatment to prevent the disease, then low maintenance, disease resistant plants should be selected. You may want to avoid trees or shrubs that produce messy fruits, foul smelling fruits, or fruits that attract lots of unwanted birds, animals, or insects.

Plant Sizes

When selecting plants, be sure to consider their mature sizes, not their size at time of purchase. When planting them, be sure to arrange and space them based on how large they will be at maturity instead of their current size.

Amount of Sun or Shade

Most plants grow best in either full sun, partial sun/shade, or full shade. Consider where each plant is going to be planted and the amount of sun or shade it will get in that location year-round (which may differ based on the season) when selecting plants for your landscape design.