Fall is best time to fertilize your lawn

Question: 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?

I normally fertilize my lawn just twice a year. I consider the fall application more important than the spring application. Anytime from now until the end of November is effective. You will see a quicker response if you apply it sooner. Fall lawn fertilization keeps the grass green all winter and into early spring. It allows you to wait until May to apply a spring fertilization. Then the spring application lasts through the summer. I prefer a lawn fertilizer which has a 3-0-2 balance of nitrogen-phosphorus-potassium. A typical formulation would be 15-0-10 or 18-0-12. An organic lawn fertilizer would be more like 9-0-6. The numbers do not have to be exact, but approximately in this ratio. I like to have at least 1/3 of the nitrogen in a slow release form since nitrogen is very soluble and some leaches below the grass roots. The most effective slow release mechanism is coating or encapsulating some of the nitrogen with sulfur or a poly coating. There are also chemical nitrogen compounds such as methylene urea which are slow release. Check the “guaranteed analysis” to see if some of the nitrogen is slow release. The analysis label will also list iron, which is also helpful, even in small amounts. Special lawn fertilizer formulations for fall application (usually called “winterizer” blends) are also suitable. They have a greater amount of potassium (the 3rd number). Liquid applications by lawn care companies do not last as long as granular fertilizer. They are satisfactory as long as they are applied more frequently.

If you have broad leaf weeds in you lawn, a weed and feed product is a convenient way to apply both fertilizer and weed killer at the same time. Weed killers are most effective in the fall because weeds are transferring food to the root system for winter storage. The weed killers also get transferred to the roots for a more complete kill.



Allen Wilson

Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture.

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