Cool season turfgrasses in upper Midwest lawns benefit from dormant fertilization

Applying a winterizer fertilizer this time of year will help rebuild turf by providing the nutrients needed to build up the root system and leave you with a healthier, thicker lawn in the spring.

Autumn leaves drift down from the trees, memories of hot summer days are fading as you tuck the lawn mower away for the season. Before you head off to hibernate, there is one more task left that can help improve your lawn. Fertilizing your turf this time of the year, sometimes known as a “dormant” or “winterizer” application, can result in a healthier, thicker lawn.

Winterizer fertilizers help the grass build a larger root mass in the fall resulting in a healthier lawn. A stronger root system helps to provide a lawn with better tolerance to heat and drought stress. A healthy turf is also better able to withstand insect and disease problems.

A few years ago, dormant turf fertilizers contained higher rates of phosphorus which were believed to help with root development. This has all changed since researchers found that grass plants utilize nitrogen for root growth in the fall once grass blades stop growing. A basic winterizer fertilizer might be a 24-3-12 or may not contain phosphorus at all as with a 24-0-12.

Another benefit of fertilizing the lawn this time of year is that it greens the turf without causing a flush of growth. Nutrients stored in the plant in the fall are then available for plant development in the spring. Paul Rieke, professor emeritus of the Department of Crop and Soil Sciences at Michigan State University, related that “one of the advantages of a dormant application of nitrogen is that the turf is green in the spring but does not result in the rapid flush of growth that occurs with an early spring (April) application.” Early spring applications often stimulate a rapid flush of growth at the expense of root development. This lack of root growth in spring brings stress to the lawn once hot, dry summer conditions appear. Using a fertilizer at the dormant stage in the fall reduces the need for early spring fertilizers.

The lack of rain in June to early July this past summer left many lawns thin and weak, leaving turf more vulnerable to disease and insect attack. The thinned turf provides openings for weed invasion. Our cool season grasses, Kentucky bluegrass, Perennial ryegrass and fine fescues recover from summer stress during the cooler temperatures and consistent moisture in the fall. Use this time of year to help rebuild your turf by providing nutrients needed to help buildup the lawns root system. A little extra effort this fall will be reflected in the spring with a thicker turf.

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