University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Fall Root Growth for Trees and Turf

October 14, 1999

While fall is typically thought of as a time for clean up in the yard, it is also an important time for many plants to grow roots. Cultural practices can help encourage rooting of plants such as trees and turf.

Even though most of the area received significant rain at the end of September, water is critical for rooting and winter preparation for lawns, trees, shrubs, and other perennial plantings. If conditions turn dry, water landscape plantings to assure they go into winter in good shape.

Fall fertilization can also help root systems of lawns, trees, and shrubs. For lawns, early and late fall are suggested times for fertilizing. Right now we are somewhat in between, as the next suggested time would be about Halloween or slightly later. Wait until top growth is about done for the year, but the soil is not frozen.

Trees and shrubs, although turning color and dropping their leaves, can benefit from a fall fertilizer application. Soils are still plenty warm for significant root growth that can be helped by fertilizers. Don't overfertilize trees and shrubs, however, either by a heavy rate or too frequent of application. Fertilizing trees is often based on tree growth; so if the tree is putting on plenty of growth, it may not need fertilizer. If the tree was already fertilized in 1999, skip this fall. If in doubt, avoid overfertilizing.

When fertilizing trees, it's best to get the fertilizer into the soil, especially if grass is growing over the tree root zone. Root feeders work well. Apply most of the fertilizer near the dripline of the tree and slightly beyond. Fertilize during the month of October. Apply about three pounds of nitrogen per 1,000 square feet of area under the tree, adjusting this rate somewhat according to site and growth factors.

Finally, help root systems on compacted soils by aerating. Core aerating is very beneficial for lawns, but can also help shade trees. October is a good time for aerating, assuming soil moisture levels are adequate. Aerate in two directions over the lawn, at right angles to each other, for best results. It's suggested to leave the cores on the surface when the process is completed.


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