Fall Fertilization Can Help Protect Plants From Winter

October 13, 1991|By Thomas G. Ford Extension Service horticulture consultant

Last month's gardening supplement to the Carroll County Sun contained conflicting information regarding the fertilization of trees and shrubs in the fall.

The University of Maryland Cooperative ExtensionService's research has shown that fall fertilization does not increase the risk of winter injury, nor does it cause plants to grow longerinto the winter season.

Most horticulturists concur that nutritionally-stressed plants are more likely to be injured by freezing temperatures than plants fertilized in the fall.

Frank Gouin, our extension specialist for horticulture, likens fall fertilization to adding an anti-freezing agent to the plants' cells and tissues.

Fall fertilization increases thenitrogen levels in flower and leaf buds. The elevated nitrogen levels in these buds allows the plants to withstand even the coldest of temperatures.

It's true some horticulturists believe fall fertilization increases the risk of winter kill.

But in my 15 years in the industry, I have never seen a fall application of fertilizer promote autumn growth. The only time that I have witnessed late-season growth has been when a plant has been defoliated by insects or disease, or when a novice gardener has heavily pruned back a tree or shrub.

Fall fertilization has no effect on the hardening process that takes place each autumn.

The leaves and buds on plants are photo-receptors.They perceive changes in day length and adjust the plant's physiological and hormonal systems accordingly.

If a novice gardener cuts back a shrub or tree severely, they often remove the terminal buds. The terminal bud is one of the most important structures on the tree. As long as it is intact, it suppresses axillary growth up and down thestem.

Upon its removal, dormant axillary buds will break and grow. These buds will compete with each other to establish dominance. Theemergence of a terminal bud is essential to restoring the plant's natural hormonal balance.

New growth emerging after severe autumn pruning will result in winter kill. Landscape managers and homeowners should delay any severe pruning until after the plant has gone completely dormant.

One of the best ways to limit winter injury to your landscape is to apply a balanced fertilizer around your shrubs at the rate of two pounds of 5-10-10 per 50 square feet. Organic fertilizerslike cotton seed meal or bone meal also could be used.

Information: 848-5013.

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