Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

8/16/04

Contacts:
Amber Anderson, Plant Health and Protection, aander@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Garden Column for the week of Aug, 20, 2004

Soil: The Other Half of the Story

By Amber Anderson
Plant Health and Protection Student
Iowa State University Extension

Children often have a tendency to only tell part of the story. It is up to you to coax out the other half of the story and figure out what really happened in a given situation. This also occurs when diagnosing plant health problems, only half of the story is told by the above ground plant tissue. It may take some digging around to find the 'root' of the problem.

Here are some common tree and shrub health problems that you may be overlooking or misdiagnosing if your attention is only given to the top portion of the plant.

Too Deep
Some trees are planted too deep. Trees should have a flare at the bottom of the trunk rather than going straight into the ground like a telephone pole. Trees planted too deep may show more stress signs and have a shortened life because of poor root growth, but signs of this problem may not show up until many years after planting.

Solution: When planting a new tree, make sure to find the root flair on the tree and plant it at the correct level. Do not just plant it at the level it was in the pot because the plant may have been placed too deep in the pot it was purchased in.

Round and Round
If planted incorrectly, the roots of some trees may grow around the center trunk restricting the movement of water and nutrients. This problem, called girdling, does not lead to a quick death; instead the plant is slowly 'choked' by its own root system. Maples and some species of oaks are susceptible to this problem.
Solution: Spread out the root ball of trees when planting. Take care to see the tree is not planted too deep.

Too Much or Too Little Fertilizer
Soils provide most of the nutrients required for plant growth. Iowa soil normally is quite fertile, but there may be occasions where plants lack nutrients. Some of these situations include areas where a large amount of plant matter has been taken off for several years or in areas where the topsoil has been removed during construction, such as in new housing developments. While some fertilizer may benefit the plant, more is not always better. Excess nutrients can lead to burn and toxicity in the plant.

Solution: Soil tests can be used to check for nutrient deficiencies. Often this soil test will be returned with a recommendation for fertilizing. For more information, visit the Iowa State University Soil Testing Lab's Web site: http://www.agron.iastate.edu/soiltesting/.

Too Dry or Too Wet
Varying soil moisture conditions can put many stresses on plants. Even if they do not kill the plant, these conditions may make the plant more susceptible to other problems.

Dry soil not only causes plants to lack enough water for normal growth and development, but also limits nutrient uptake. However, too much of a good thing can be harmful. Some soils, especially those high in clay, can hold too much moisture next to the roots long after water has drained off the surface. Since roots need to breathe as humans do, they are essentially drowning or suffocating. This water is not even available for plant use because it is held so tightly by the clay. Also, wet conditions lead to increased fungal growth and spread of disease because spores can be splashed by raindrops.

Solution: Select the proper plant for the site conditions. For example, if an area is often wet, plant species that are more tolerant of wet conditions, such as a river birch, green ash or willow, rather than an evergreen such as a white pine.

If trees or shrubs lack moisture, watering more deeply and less frequently will allow proper development of the root system.

Hard as a Rock
In compacted soils, the large pores in the soil that normally facilitate water and gas exchange have been packed down into smaller ones that do not allow those processes to take place as efficiently. Compacted soils slow root growth, limiting the area the plant has to extract water and nutrients.

Solution: Avoid things that compact the soil such as walking and driving over it or working the soil when wet. Adding organic matter such as mulch tends to help avoid soil compaction.

Problem Reservoir
Problems from previous crops can be harbored in the soil. Nematodes, many types of fungi and insects are some of the pests that may build up in the soil. Even with perfect care, this problem may still show up.

Solution: If a tree or shrub has recently died in an area, determine the cause and plant a species resistant to that problem.

Next time you have a sick plant, remember to look at the whole story. Parts of the plant below the surface can be just as important as the parts you can see. You may have to dig a little deeper to find the real problem.

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Editors: There are no photos available for this column

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