I forgot to fertilize the lawn last fall, and we paid for it all summer because clover and other weeds took over the grass. A weedy lawn is often a good indicator of insufficient fertilizer. While most people fertilize lawns in the spring, many horticulturists believe a fertilizer applied in October leads to healthier, more drought-resistant lawn. Summer is the worst time to fertilize with typical high nitrogen lawn fertilizers, because the nitrogen stimulates faster growth, stresses the grass and leads to potential disease, higher water use and more mowing. Mid-summer fertilization can also contribute to thatch buildup.
The most important nutrient for healthy grass is nitrogen, which gives a lawn its even green color. Most fertilizers contain nitrogen, phosphorus and potassium, the three macronutrients essential to good plant growth. In addition to these, a fertilizer may also contain iron, sulfur or micronutrients. Some fertilizers are inorganic and others are organic. Inorganic fertilizers have a higher analysis than organic fertilizers.
The analysis is the three numbers on a fertilizer package. The first number is nitrogen, the second number is phosphorus and the third number is potassium. A fertilizer that contains all three macronutrients is known as a balanced or complete fertilizer. An analysis of 21-0-0 means the product contains 21 percent nitrogen, zero phosphorus and zero potassium. Many inorganic lawn fertilizers have a nitrogen number higher than 21, although a 21-0-0 fertilizer works well. Most organic fertilizers have a nitrogen value of 10 percent or less. They operate more slowly than an inorganic fertilizer, but they usually also contain active soil microorganisms that build soil health, something inorganic fertilizers don’t do. A healthier soil leads to healthier plants.
Soil type can influence which fertilizer you use. Inorganic slow release or organic fertilizers are best on a sandy soil to prevent leaching of fertilizer into surface or ground water. Clay soils and soils high in organic matter can hold an inorganic fast release fertilizer in place and reduce leaching.
You should need less fertilizer each year if you leave your grass clippings on the lawn. Grass clippings recycle some of the nutrients you have applied. Grass clippings do not increase thatch accumulation in lawns.
By fertilizing in early October while the grass is still green, and again at least two to three weeks before the ground begins to freeze, you may be able to avoid an April fertilizer application next year, but still have a beautiful lawn.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.
