   Planting Trees and Shrubs: Beyond the Myths - July 15, 1998 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County How many readers can identify with the following scenario? You have just come home after a trip to the local nursery. First, you unload a beautifully grown, locally adapted tree in a five-gallon container. Next, you hoist out a couple of bags of compost that you will use to amend the soil. You spend an hour digging a hole (quite possibly in caliche) that is twice as deep and three times as wide as the five-gallon container and amend the soil with the newly purchased compost. Before planting the tree, you put half the amended soil into the hole, remove the container and place the tree on top of the mixture. Finally, you backfill the tree with the remainder of the amended soil, mix up some vitamin B1 and fertilizer, and water your new tree with a satisfied gleam in your eye. Over time, you nurture and care for this tree and all is rosy until three years later, the tree dies without explanation or warning. How could this be? After all, you explicitly followed the instructions in your well-respected "gardener's reference book." If you have had this experience, you are not alone. Most gardening books and guides instruct you to plant this way, but recent research by Dr. Jimmy Tipton of the University of Arizona has shown these guidelines to be inadequate. To understand why, let's review the natural history of trees growing in arid environments. In the desert, water is the main factor limiting plant growth. Native trees overcome this by growing roots outward from the stem and exploiting the available soil moisture over a large area. These roots are not deep (one or two feet), but may extend four or five times the diameter of the crown. Proper planting of nursery grown stock should encourage this root growth pattern. Another factor that affects tree survival is planting depth. Trees planted too deep can get crown rot and literally drown. This happens because the above ground portion of the tree actually has openings (called lenticels) that allow gases to flow in and out so the tree can breathe (respire). On the other hand, roots are more water resistant. Proper planting must also maintain this distinction between above and below ground portions of the tree. Encouraging a wide-spreading root system and maintaining the proper planting depth can be achieved by using the following guidelines. First, till an area three to five times the diameter of the container and dig a hole in the center of the tilled area slightly wider and no deeper than the root ball. Next, remove the tree from the container, cut any circling roots and vertically cut one-fourth to one-half inch deep four times around the sides and twice across the bottom. Making sure the top of the root ball is level with or slightly above the soil surface, fill the hole with unamended soil without packing it tight. Remove the nursery stake and ties then form an irrigation well initially at the edge of the root ball and further away after a month or so. Irrigate the tree to remove any air pockets without compacting the soil. Finally, mulch the soil surface with three to four inches of organic material. Try to keep the mulch away from the trunk. Free mulch is often available from local sources. Planting trees and shrubs in this manner will encourage root growth into the native soil and minimize the number of growth adjustments the plant will make due to changes in soil type. Placing the root ball directly on undisturbed native soil will minimize settling that can cause crown rot. Mulching helps retain soil moisture. Pruning of lower branches should be avoided for the first few years. These branches contribute to diameter growth on the trunk. No fertilizer is needed during the first year unless there is a known deficiency (such as iron). Many people will reject these ideas as heresy. However, this information is backed by solid research and warrants trying. Also, there are many concepts not covered in this article such as staking, planting in caliche, watering, etc. The University of Arizona Publication: Planting Specifications: Container Trees and Shrubs has much more information on this topic. For a free copy, call 646-9113 or visit our Cottonwood Office at 2657 Village Dr. For more information about tree selection, planting, care, and other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113. Or E-mail us: mgardner@kachina.net. Be sure to include your address and phone number. |