   Selecting the Right Plant - March 22, 2006 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Plant selection is the process of matching site conditions to a plant species. Believe it or not, improper selection is a leading cause of plant failure. The most common mistake is choosing a plant that outgrows the available space. Harsh pruning often follows, which quickly becomes a maintenance nightmare. They often quickly grow back to their original size (think fruitless mulberry). Frequent pruning can also stress woody plants causing them to decline. If this sounds familiar, you really should consider replacing the offending plant with one that is more suitable for your needs. Proper plant selection results in healthier plants that perform to your expectations with little or no maintenance. Many areas within the Arizona Highlands have poor soils and/or extreme weather. Woody landscape plants must be well-adapted to our climate and in good condition prior to planting. Native and drought-tolerant species offer toughness and water conservation. These plants can be more difficult to find. However, growers have responded and increased their production. Now, many nurseries carry an ever increasing selection of native and drought tolerant trees and shrubs. There are also many tried and true favorites that perform well in our unique climate. The first decision involves deciding how much growing space is available: both above and below ground. Height restrictions, width restrictions, and available root space should all be considered. Do not plant trees and shrubs closer to a building than one half the mature canopy width. Power lines, roof overhangs, septic systems, and underground utilities should also be considered and avoided whenever possible. The Sunset Western Garden Book lists the mature size of plants suitable to our area. Roots of trees and shrubs can extend 1.5 to four times the width of the canopy. Roots of a 20 foot wide tree could spread from 30 to 80 feet from the trunk. Plants should be well adapted to the local environment. Climate zones and cold hardiness maps are available on-line and in Cooperative Extension offices. These should be considered a starting point, but localized microclimates within your property should also be considered. Consider how hot it is when you walk across a parking lot in July. The heat is being reradiated from the asphalt. Along streams and rivers it is much cooler. Cold air drains from high to low elevation so low lying areas are usually colder in winter. North and east exposures are cooler than south and west exposures. These guidelines can help you determine whether your planting site is especially hot or cold for your climate zone. A soil depth of 18 to 24 inches is sufficient for most trees and shrubs. Consider adding soil if you have less than six to eight inches. Urban soils can be compacted due to construction, vehicle or foot traffic. This limits water penetration, air exchange, and root growth and can be alleviated by loosening soil and limiting traffic – especially when the soil is wet. Soil texture on the site will determine how much water and air that a soil can provide to plant roots. Sandy soils are well drained, well aerated, and resist compaction, but require more frequent irrigation. Clay soils do not drain well, are poorly aerated, and easily compacted, but require less frequent irrigation. Knowing your soil texture is useful when selecting plants and can be determined by a Cooperative Extension Master Gardener. Soil drainage can also be reduced by shallow bedrock, caliche, or the presence of clay. Other factors that should be considered are water quality, insects, diseases, birds and mammals. Salinity of irrigation water can be a serious problem in some areas of the Verde Valley (especially near the Salt Mine in Camp Verde). Large amounts of dissolved salts interfere with the plant's ability to absorb water through the roots and can be a cause of stress. Known plant pests and diseases should also be considered when selecting plant species. The University of Arizona Cooperative Extension Publication Drought Tolerant Trees for the Mid-elevation Deserts of Arizona (3,000-4,000 ft) is available at Cooperative Extension offices or on-line at: ag.arizona.edu/pubs/garden/az1239.pdf. This publication lists trees by size and offers several choices for each size class. I am also working with the Arizona Department of Water Resources to develop a list of drought-adapted trees, shrubs, grasses, and perennials for the Prescott Active Management Area. This list also has many plants suitable for planting in the Verde Valley and is available on-line at: www.azwater.gov. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |