In the Garden:
Western Mountains and High Plains
October, 2007
Regional Report

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Our cool-season grasses need a high-nitrogen fertilizer in fall.

Winterizing Cool-Season Lawns

Every fall homeowners ask me, "Is it really necessary to winterize my lawn?" Just visit any garden store and you'll see pallets stacked high with products for winterizing. In our region it is important to select a fertilizer high in nitrogen. Understanding how to read the numbers on the fertilizer bag will help you make the correct choice.

Many so-called "winterizers" contain higher percentages of phosphorous and potassium than nitrogen. These numbers are marked on the package as in 10-20-25 -- 10 percent nitrogen, 20 percent phosphorous and 25 percent potassium, in that order.

Those who advocate using these high phosphorous and potassium fertilizers point to research that has shown the need for these formulas. But the research is based on warm-season grasses, such as zoysia and Bermuda grass. These grasses are not typical in our climate except in extreme southern locales. The most important nutrient for cool-season grasses, including hybrid bluegrasses, turf fescues, and ryegrasses, is nitrogen.

Fertilizer Tips
Fertilizing with a high-nitrogen formula in the autumn is one of the most important lawn fertilizations of the year. But with the widespread promotion of phosphorous and potash fertilizers for fall, high-nitrogen products may not be readily available. So shop carefully or use the higher-nitrogen fertilizer left from earlier applications. Look for a 20-20-10, 15-4-4, 46-0-0, or 24-0-0, or something equivalent.

Apply fertilizer while the grass is still green and before the ground freezes. The grass roots are actively growing and will store food reserves to last throughout the fall and winter. Carbohydrates help with increased cold hardiness. At the same time, your lawn will thicken up and maintain its deep green color.

It's also important to keep fallen leaves off the lawn because they reduce the lawn's ability to grow and photosynthesize. Never scalp your lawn in the fall by mowing too short. Mowing higher will leave more leaf surface to produce more carbohydrates. Plus, a longer lawn is less prone to fall weed seed germination before the turf goes dormant.

Maintaining your lawn properly throughout the fall will pay big dividends next spring.


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