Fall Lawn Fertilization

Fall lawn fertilizationQuestion: I was planning to fertilize my lawn when a neighbor told me I should wait until October. Is this the wrong time to fertilize? I saw a lawn care truck fertilizing in my neighborhood last week. When is the best time for fall lawn fertilization?

Answer: You did not mention the condition of your lawn. Is it losing its dark green color? When was the last time you fertilized? I am assuming it is not looking its best.

In general,  September and October are the best months for fall lawn fertilization. When you fertilize during this time period depends upon the condition of your lawn. If you are satisfied with the looks of your lawn right now, wait a month or so to fertilize. However, fertilizing now will give you a rapid improvement in most cases.

One of the great benefits of fall fertilization is that it not only gives immediate results, but it also carries over into spring. Fall is the time when grass makes a lot of new growth under the ground. New roots and rhizomes (underground stems) cause turf to thicken. Food produced by the leaves is stored for the winter and next spring. Early October fertilization lasts longer into the spring. September fertilization gives more immediate benefits.

Fall fertilization also keeps grass green longer into the fall. It stays green even after the temperature has gotten low enough that new leaf growth stops.

Most brands of lawn fertilizer have developed formulas for fall fertilization. They generally contain more potassium which makes grass more resistant to winter desiccation. However, I have found that almost any lawn fertilizer works well in the fall. Research has shown that nitrogen is taken up by grass roots and used to make amino acids which are stored in grass crowns and roots. These amino acids are available for immediate use in early spring when soil is too cold for roots to take up nitrogen. The result is faster green up in the spring.

Read the “guaranteed analysis” label to make sure lawn fertilizer contains iron. Iron causes grass to turn dark green, sometimes almost over night. Look for sulfur also. Sulfur reduces the pH of our alkaline soils which also improves grass growth. I like to apply straight garden sulfur or combination iron and sulfur compounds every 2 to 3 years to make the soil less alkaline. Fall is a great time to make this application.

Wait until late October or November to fertilize trees and shrubs. By then, top growth has become dormant, but roots can continue to take up fertilizer until the ground freezes. Stimulating new growth now will make woody plants more susceptible to winter damage. Don’t be concerned about the small amount of fertilizer taken up by tree roots growing under the lawn.

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