Washington State University Extension

Garden Tips


GARDEN TIPS – Written by Marianne Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published September 18, 2016

This summer was not as hard on area lawns as the past three preceding excessively hot summers, but many area lawns could still benefit from a little attention this fall.

Fall is the most important time of year for fertilizing your lawn. Applications of fertilizer in early September and again in late October to early November are the two most important times of year to fertilize your lawn. Even though grass top growth slows during the shorter, cooler days of fall, grass plants continue to grow sideways by producing tillers that become new grass plants. By fertilizing in late fall, you promote the production of healthy tillers that will result in a denser turf next year.

Fall mowing practices are key in protecting the health of those new tillers that are being formed in the fall. Keep mowing your lawn at the recommended height of 2.5 to 3 inches until top growth slows. After top growth slows to a stop, Kelly Kopp, Utah State University turf grass specialist, recommends gradually lowering the height of the lawn to about 1.5 inches. Leaving lawn grass extra-long in the fall can lead to fungal disease problems over the winter. Cutting the grass very short all at once will damage the established grass plants and the new tillers. Be sure to lower the height gradually.

When it comes to fertilization, lawns do not need a specialized “winterizing” fertilizer containing higher levels of potassium and phosphorus, despite advertisements seen at this time of year. No research indicates that these fertilizers are beneficial to the cool season grasses used for area lawns. When applying fall fertilizers you should be concerned primarily about nitrogen. The last application of fertilizer in early November should have most of the nitrogen in a quick-release form that is readily available to the grass as it begins to go dormant with cold weather. Kopp points out that research shows that late fall fertilization “provides the most benefit and drought tolerance to the lawn the following summer.”

Last year’s heat and drought left many lawns vulnerable to invasion from broadleaf weeds. Prostrate spurges have taken hold in numerous area lawns. These spurges have tiny leaves and form dense, ground-hugging mats. Spurges get started along lawn edges next to pavement or in open spots. Each plant is prolific, producing thousands of seeds. Seeds germinate in early summer, grow quickly, and flower within five weeks of germination. This provides time for more than one generation per year. The good news is that spurges are annual weeds and will die out with frost. Fertilizing and mowing to promote a dense turf will help crowd out the spurges next year.

During the growing season, spurges are difficult to control with herbicides because they are resistant to the typical dandelion broadleaf weed killers containing 2,4 D. The spurges are more effectively controlled with lawn weed control products containing triclopyr. Pre-emergent herbicides applied prior to germination in both lawns and landscape beds can also help in the fight against the spurges.

A fall application of a broadleaf weed herbicide will control most other perennial broadleaf weeds in lawns, such as dandelions, plantain, clover, black medic, and others. The results of a fall herbicide application is often not immediately apparent, but by next spring most of these weeds will disappear. However, there is no need to treat your entire lawn if you only have a few weeds. Treat these individually or pop them out with a weed popper.

Remember, a little attention to your lawn this fall will pay off next spring.

Garden Tips, WSU Extension, Benton County, 5600-E West Canal Drive, Kennewick, WA 99336-1387, 509-735-3551, Contact Us

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