By Lisa Johnson, Extension Educator
Lawns benefit from fertilization at least once a year with nitrogen-containing products to maintain turf density, prevent runoff, and retain the ability to shade out weed seedlings. If you only do it once, the most important time to fertilize is now, around Labor Day into early September! Apply no more than one pound of actual nitrogen per 1000 square feet per application. Be sure to check the ‘N’ (nitrogen) number on the label of your product, which indicates the percentage of nitrogen present in the product. You will need to do a little math to calculate how much of it is needed for one pound or less per 1000 square feet if it is not listed in the instructions.
Autumn fertilization in early September promotes faster green-up and growth next spring. For conventional lawn fertilizers, ideally, select one with at least 25-50% slow release (insoluble) nitrogen—this information should be written on the bag. Avoid blends with a high proportion of quick-release, water soluble nitrogen. Higher solubility means there is a great chance that the nitrogen will wash through the soil and not help your lawn. Sandy soils or soils with high water tables are particularly concerning since the nitrogen may get into groundwater.
While turfgrass grown in sun needs one pound of nitrogen per 1000 square feet; turfgrass grown in shade needs less; one-half pound of nitrogen per 1000 square feet. Don’t add more in shade thinking it will get you stronger turf, because it will just result in weak lush growth that may be more susceptible to diseases like powdery mildew or rust. You can reduce the amount of fertilizer you need to apply annually by up to one application per year by leaving clippings on your lawn when you mow.
Want to learn more? The Publication publication titled ‘Lawn Fertilization’ will get you started. If you have a lawn spreader this publication ‘Calibrating and Using Lawn Fertilizer and Lime Spreaders’ will demystify the math for you. You can use organic lawn fertilizers, but be aware that they contain less soluble nitrogen, so you may not see the effect on your lawn right away as soil micro-organisms must break down organic products to release the nitrogen, unlike some conventional fertilizers.