Question: I have noticed stores are advertising fall lawn fertilizer. Is this a good time to fertilize lawns?
Answer: Fall (Sept.-Oct.) is not only a good time to fertilize lawns, it is the best time. Fall fertilization not only gives you an immediate response with a greener, thicker lawn, the benefits carry over until next spring.
The cooler temperatures and shorter days stimulate root and rhizome growth in Kentucky bluegrass lawns. Rhizomes are underground horizontal stems which produce new shoots that make the lawn thicker. Fertilizing now stimulates that natural growth process.
Some of the fertilizer nutrients applied in the fall are used to produce amino acids which are stored in crowns and roots over winter. When the first warm days of spring arrive, there is already food available for new growth even before the soil is warm enough to pick up nutrients from the soil.
Lawn fertilizer formulations are changing. The trend is to put less and less phosphorus in lawn fertilizers. Some states have banned phosphorus from lawn fertilizers because of its accumulation in runoff and ground water. Most of our soils contain adequate amounts of phosphorus.
Another trend is to increase the percentage of slow release nitrogen. I prefer lawn fertilizers with one-third to one-half of the nitrogen in coated, slow release form. A variety of coating thicknesses are used to spread the release over several months. Check the fertilizer guaranteed analysis label to see if part of the nitrogen is in slow release form.
Special fall lawn fertilizer formulations are available which contain extra potassium. Potassium is important in preparing grass for winter cold and drought. I like to see up to 50 percent as much potassium as nitrogen. A common formulation would be 20-0-10 or 20-5-10.
If weeds such as dandelion have developed this summer, you may want to use a weed and feed formulation which contains weed killer as well as fertilizer. Or the weeds can be sprayed with a liquid lawn weed killer.
Allen Wilson can be contacted at firstname.lastname@example.org.