By JoAnne Skelly — At Cooperative Extension we recommend that if you only fertilize your lawn once per year, do it in the fall. Our cool season turfgrasses have a resurgence of growth when the temperatures cool. A fall fertilizer application helps the grass recover from summer’s stress and can prolong the green through most of the winter as well as help speed green-up in the spring.
JoAnne Skelly
And, because the grass is stronger and healthier, fall fertilizer improves drought tolerance next year. According to the Utah Division of Water Resources, “Late-fall fertilization benefits turfgrass by increasing the plant’s carbohydrate reserves in the stems and rhizomes. Carbohydrates help the turfgrass resist winter injury and aid in stress resistance the following spring and summer. In addition, late-fall fertilization doesn’t force as much leaf growth in the spring as an equivalent amount of spring fertilizer would, so carbohydrate reserves are not exhausted as quickly.”
Credit: Photo by Wendy Hanson Mazet, Cooperative Extension
The ideal time to fertilize is after average daily temperatures are below 50 degrees Fahrenheit for three or more days in a row and after the last mowing of the year.
All fertilizers show a three number formula on the package. The numbers refer to amount of nitrogen (N), phosphorus (P) and potassium (K) in the product. These numbers are the percentages by weight of nitrogen (N), phosphate (P2O5) and potash (K2O). A lawn fertilizer with an analysis of 25-5-10 has 25 percent N, 5 percent phosphate (P) and 10 percent potash (K). My preference is a generic 16-16-16 fertilizer in the fall, instead of my usual spring 21-0-0 fertilizer. Higher phosphorus and potassium in the fall help the grass have strong roots and carbohydrate storage for winter into spring.
When I look at “fall lawn food” products online, I find many different analyses of contents. One was an 8-12-16, which is not bad for fall with lower N (no need to encourage leaf growth in the fall), some P and K. Another is a 28-0-10. I’m not sure grass needs that much nitrogen at this time of year. However, since phosphorus helps not only with root development, but also with many vital growth processes, I want P in my fall lawn fertilizer for a healthy lawn. K is important for biochemical reactions in the plant, cell health and water movement in and out of cells.
Read your label when buying a fall lawn fertilizer. You might find a 16-16-16 or something similar to be less expensive than a brand name.
— JoAnne Skelly is an Associate Professor and Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at skellyj@unr.edu.
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