no. 7.229

Xeriscaping: Trees and Shrubs

Quick Facts...

• Xeriscaping offers an opportunity to select plants compatible with local conditions.
• When selecting woody plants, consider soils, drainage, exposure and irrigation method.
• Plant trees and shrubs in areas separate from irrigated lawns.
• Water xeric trees and shrubs just as much as other plants until established, usually two years.
• Once established, gradually reduce watering frequency.
• Frequent shallow watering promotes shallow roots and defeats the purpose of xeriscaping.

Selecting woody plants for a reduced-water landscape or xeriscape (zer-i-skap) requires careful consideration. Woody plants such as trees and shrubs are a major component in the landscape and a long-term investment. In addition to aesthetics and function, look at soil, drainage patterns, exposure to heat and wind, and how the site is irrigated.

Aesthetics and Function

Colorado landscapes require plants that can adapt to a drier climate than many cultivated landscape plants. Xeriscaping offers an opportunity to select plants that are more compatible with local conditions and able to thrive when other landscape plants cannot. In recognition of our local environment, it often is more practical to select plants that can tolerate drought. We can enjoy a landscape that reflects its surroundings better than the New England landscapes we too often try to establish and maintain at great effort. Many people consider it a challenge to use locally adapted plants to develop a creative landscape that represents a unique Colorado style.

With careful selection, you can blend plants of varying colors, textures and densities into an attractive, lower-maintenance landscape. Xeric plants offer a wide range of foliage density, color and texture, as well as plant forms, with which to work. Some, like rabbitbrush and apache plume, have small leaves, imparting a fine texture. Others, like sage, have grayish or silvery foliage. Still others, like yucca, may be spiny and stiff-looking. These plants may not look quite like the plants you may be used to. With proper planning, you can create a more interesting landscape than your neighbor's without sacrificing the comfort and beauty of your yard. Conserving water by substituting plastic and gravel for plants will not add enjoyment to your landscape or value to your home.

Use xeric plants for the same functions as more traditional types. Pines and upright junipers, for example, make excellent screen plantings under low irrigation. Spruce is best used in heavily irrigated sites or low, moist areas. Xeric plants also are excellent for mass plantings on steep banks, particularly on hot south and west exposures.

Shade trees for the patio and south exposures of the house might be hackberry, honeylocust or Burr oak rather than silver maple, weeping birch, aspen or cottonwood.

Trees and shrubs are best planted in beds or islands separate from the lawn unless the lawn also is a low-water type.

Soils, Drainage and Exposure

Before selecting plants, evaluate the site's soil, drainage and exposure. Consider all three factors together, because each affects the others. If the soil is a heavy clay, it will have poor internal drainage even on a slope. The same soil on a south or west exposure will dry quickly, shrink and crack, requiring slow but relatively frequent watering. Dense clay soils are low in oxygen and do not lend themselves well to plant growth. Most xeric plants, while tolerating low water, cannot function well in soils low in oxygen. The better a soil is prepared through addition of organic amendments prior to planting, the better the plants will do.

In very heavy soils where improvement of subsoil drainage is not feasible, it usually is best to plant trees and shrubs on berms (mounds) of well-drained, loamy soil brought to the site. Berms should be at least 24 inches high.

Select shade-tolerant plants for north exposures. There are fewer of these than species for full sun because most xeric plants thrive best in sunny exposures. Those that do tolerate shade generally require more water. This can be somewhat offset by using organic mulches such as wood chips.

Establishment of Plants

Regardless of how drought-enduring a plant may be, relatively frequent watering is needed until the plant is established. Most woody plants take at least two growing seasons to establish, depending on how well the soil has been prepared. Once plants are established, gradually reduce watering. Avoid frequent, shallow watering, however, because this tends to encourage shallow roots and thus defeats the goal of xeriscaping.

Some Selections

While not a complete list, the trees and shrubs in Tables 1 and 2 are suited to a xeriscape. Some may be uncommon in many nurseries but available from wholesale suppliers. They can be ordered through your local nursery.

For more information, see the following Planttalk Colorado^TM script(s).

• 1748, Pinon

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