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Index : Landscape Plants
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- 43. It's a Great Time to Plant Trees - Top
- Autumn is a great time to plant trees in Tucson. Trees planted now have near ideal conditions in which to establish themselves. Cooler temperatures and less intense sun means less stress on new plantings. Warm soil temperatures encourage root growth well into November. This is especially important for the success of new trees.
Avoid purchasing trees that have had all their lower limbs removed. Half of the tree's branches should originate on the lower two-thirds of the trunk. Poor quality trees have no branches along the lower half of the trunk. These trees are weak-trunked. When the supporting stakes are removed the trunk is too weak to hold up the leaf canopy, and the tree bends over.
Select trees with trunks that have a gradual taper. The lower trunk should be thicker than the upper trunk. This is a good indication of trunk strength. Trees that are supported by stakes may or may not be weak. If the stakes are removed, the tree should be able to stand on it's own.
Trees must be planted at the right depth and receive the right amount of water is they are to establish themselves and flourish. Planting too deeply is the most common reason why trees fail. Close behind is under watering, particularly when trees are young.
A commonly held belief, here in Tucson, is that trees should be planted in very large holes; much deeper and wider than the root ball. Through research studies conducted here in Tucson by the University of Arizona and by a number of other Universities around the country, new planting specifications have been developed. These specifications call for the digging of a planting hole no deeper than the root ball. This is to prevent the tree from sinking in the hole, caused by the loosened soil in the bottom of the hole settling. The deeper the hole, the more settling that occurs, and the deeper the tree will sink.
Tree settling often results in the trees death because soil fills in around and over the base of the trunk causing crown and root rot. This damage can develop within months of planting. Other times the injury, and resulting demise of the tree doesn't show up for years.
In well drained soil, you want to locate the topmost roots in the root ball so that they will be level with the soil surface. Check to be sure that there is not an excess layer of soil already covering the root ball. As little as half an inch of excess soil over the root ball can inhibit or prevent water and oxygen from entering the root ball. Only mulch should be placed over the root ball.
To determine whether your soil is well drained or poorly drained, dig a hole the size of a 5 gallon container. Fill it with water and allow the water to drain out. Fill it with water again. Water should drain out of the hole from this second filling within 24 hours. If it doesn't, your soil is poorly drained.
In poorly drained soil take extra precautions to ensure that roots are not suffocated by the water saturation typical of these soils. The top few inches of the root ball should be planted higher than the surrounding soil and irrigation managed accordingly. Dig the planting hole to allow the top of the root ball to sit higher than the surrounding soil. After planting, mound soil to create a gentle slope down from the top of the root ball. The planting hole and the resulting mound should be at least five times wider than the root ball. This technique will help prevent the top portion of the root ball from becoming saturated during rain or irrigation. The top of the root ball will dry out quickly in summer on some sites, so be prepared to provide some extra water, especially until the tree becomes established.
Regardless of whether the soil is well or poorly drained, apply a surface mulch after planting. Mulches are spread over the soil surface around the trunk and several feet out. The best mulches to use are the organic types, such as forest mulch, desert compost, or pine straw. The mulch layer should be three to four inches thick. As the tree grows, should too the mulch layer. Continue to expand the diameter of the mulched area to blanket the root system. Remember, tree roots can grow up to three feet in length yearly.
During the initial establishment period after planting, water daily. After two or three weeks the days between waterings can gradually be increased. By late autumn trees should be receiving two to three waterings weekly. In winter when temperatures are cool, one watering per week should be sufficient. But when warm weather arrives in the spring, watering may need to be increased.
Once established, usually one year after planting, desert adapted trees such as palo verde and mesquite will need little or no supplemental irrigation. Desert tolerant trees such as live oak and Arizona ash will continue to require some regular watering.
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Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona.
Material originally appeared in Arizona Daily Star gardening column, on October 5, 1997.
- Updated: October 5, 1997
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