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Proper Planting Depth

July 18, 2001

This is not a disease problem, but it certainly promotes diseases. The Plant Clinic receives many tree samples with top dieback; branch death; yellowed, smaller than normal leaves; or other symptoms of stress. Sometimes the cause of the problem is easy to detect. There may have been construction and obvious root injury in the area. Other times, the tree is infected with Verticillium, or a root rot fungus makes itself known by producing fruiting bodies on the trunk. More often than not the tree looks puny, and samples consist of dead twigs. We may spend many days incubating or culturing samples only to find out later that the tree was planted too deeply.

If you have a tree that fits this description, step back and look at the base of its trunk. Tree trunks should have a flare at the base. If they look like telephone poles, with the same trunk diameter at 5 feet off the ground as at soil level, then the tree was planted too deeply.

David Williams and Floyd Giles of the Department of Natural Resources and Environmental Sciences wrote a fact sheet a few years ago called "Planting Trees." They state that all woody plant materials should be planted at the same level as they were growing in the nursery. The planting hole should not be dug deeper than the depth of the root ball so that the root ball can't settle with time. I think most of us know how deep to plant a tree, but many make the mistake of working the hole too deeply and then failing to backfill and firm the soil to prevent settling. The tree starts out at the correct depth but sinks or settles with time.

The next time you see a tree without a basal flare, look at the stem growth as an indication of stress. Follow the stem back from the tip until you see the end of one season's growth. The current year's stem growth is usually a lighter color of bark, and it ends with a series of rings around the stem (1/8 inch apart) that are last year's terminal bud scar. Follow the stem down to the next set of rings circling the stem, and you can measure the previous year's growth. If the tree is only growing 1 or 2 inches per year, it is obviously stressed. Michael Dirr in Manual of Woody Landscape Plants lists how much annual growth to expect with various tree species. Most are in the 10- to 12-inch range.

Of course, other factors can stress a tree over time and cause a slow decline. Tight soils (clay), poor drainage, flooding, drought, compaction, and a myriad of other problems could be involved. Consult Report on Plant Disease (RPD) no. 641, "Decline and Dieback of Trees and Shrubs," for a discussion of other possibilities. This report is available in Extension offices or on the Web at http://www.ag.uiuc. edu/~vista/.

Author: Nancy Pataky


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