   Planting Trees and Shrubs - May 27, 2003 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Telling someone how to plant a containerized (or balled and burlaped) tree or shrub is one of the most difficult tasks I face in my job. This is because a tree planting myth has been circulating for many years. The myth says: when planting a tree or shrub, thou shalt dig a hole twice as wide and twice as deep as the root ball and amend the backfill with organic matter. For those that enjoy myths and believe this is the best way to plant a tree or shrub, then I will probably have a difficult time convincing you otherwise. However, if you believe the scientific method and peer-reviewed research, read on. Below, I present the research-based Improved Planting Standard. This method has been researched across the country under many different growing conditions and has always been shown to improve growth and survival of newly planted trees and shrubs regardless of location or species. Here are steps of the Improved Planting Standard: 1) dig the planting hole only as deep as the root ball; 2) loosen the soil in an area three to five times as wide as the root ball; 3) the point where the loosened soil meets the undisturbed soil should be rough and sloped (not glazed or vertical); 4) place the tree or shrub in the planting hole and backfill with non-amended, native soil; 5) a berm to create an irrigation well should be made just outside the original root ball; 6) place three inches of organic mulch on the soil surface but do not allow it to contact the trunk; 7) remove the original nursery stake; 8) stake only if necessary (if the tree falls over when the nursery stake is removed); and 9) irrigate the tree or shrub as necessary wetting the root ball and surrounding soil. Think about how native trees and shrubs become established to further understand factors influencing landscape tree/shrub survival and growth. In a native setting, thousands of seeds are produced and these are disseminated by various methods to a multitude of sites. Only sites with an ideal microclimate and moisture regime allow seeds to germinate and survive beyond one or two seasons. In this time, the seedling puts down a deep taproot from which lateral roots develop. The taproot does not persist in most woody plant species. The lateral roots are rarely deeper than two or three feet (they need water, nutrients, and oxygen). On a mature tree, the diameter of the lateral root system is often three to five times the height of the tree. The ideal microsite is what we strive to create and lateral root growth is what we are trying to encourage when using the Improved Planting Standard. What are the problems associated with the mythological planting standard? There are two major problems. The first involves the potential for the root ball to sink into the soft, amended soil and for the above ground bark to be inundated with water. The above ground portion of the bark is permeable to air and will not tolerate the waterlogged conditions that will likely be present. The exceptions are streamside species that have evolved to tolerate flooding. Second, lateral roots that grow into amended soil tend to stay in the amended soil. The planting hole can become much like a pot and roots will start to circle rather than utilize the surrounding native soil. These circling roots can girdle the plant as it matures. The Improved Planting Standard has been shown to establish better root systems that will support and nourish the tree or shrub throughout its lifetime. For more information, see Arizona Cooperative Extension Publication 1022 - Planting Guidelines: Containerized Trees and Shrubs. It has pictures and is available on the web <ag.arizona.edu/pubs/> or at your local Cooperative Extension office. 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://ag.arizona.edu/yavapai/anr/hort/byg/. |