Why September is a Critical Month for Cool-Season Grasses

You know it’s September when kids are back in school and holiday decorations are already in all the stores. It’s also a critical month for cool-season grasses. This is the perfect time to fertilize cool-season grasses such as Kentucky bluegrass and tall fescue. Sixty to seventy-five percent of all nitrogen applied to cool-season lawns should be laid between Labor Day and the year’s final mowing.

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September is a crucial month for fertilizing cool-season grasses. Fertilizing now will make your grass strong and dense to survive the winter months.

Fertilizing in September helps nourish cool-season grass in a couple different ways:

  • It improves turf density. Fertilizing now encourages the growth of new tillers and/or rhizomes and stolons.
  • It strengthens roots. The root system will be better able to survive the winter’s challenges as well as the stresses of next year’s growing season.

Choose slow-release fertilizer with 25 to 50 percent nitrogen. Use one pound of nitrogen for every thousand square feet of turf.

This is also the best time to repair any problems with cool-season grasses. That includes any bare spots that might have appeared, and aerating if necessary to enable the roots and soil to take up essential nutrients as the season winds down. The earlier the fixes, the better your grass will look next year, as some cool-season grasses such as tall fescue are susceptible to the winter’s harsh conditions if these repairs come too late.

Killing Dandelions

September is a great time to get your weeds under control. Make sure you choose a warm and still day to apply your herbicide!

September is also the perfect month for last-minute weed control. For weeds such as clover, dandelions, wild violets, black medic and plantain, applying broadleaf weed killer this month will help get the problem under control. Look for an herbicide with two or more active ingredients.

Be careful when using fertilizer and weed repellants around desired plants, as they may damage flowers, trees, shrubs or vegetables. Pick a calm, sunny September day when no rain is forecasted and the temperature is above 50 degrees!


  1. Linda Faust on September 10, 2016 at 2:11 am

    We live in the county and have a large front yard! We discovered small skinny worms all over our lawn, after the last heavy rain. Our yard an said they were Army worms! What are they and the damage to our grass! What lawn product do we use to solve this problem quickly!

    • Harmony Brands on October 28, 2016 at 4:16 pm

      Hi Linda, Armyworms are the larvae of a moth. The caterpillars are light green or tan in their early growth stage and dark green or brown in later stages. Full-grown larvae are 1-½ to 2 inches long and almost hairless. They can be identified by a series of green, yellow, or brown stripes down the length of their bodies. They primarily eat grass blades, but will also eat some vegetables, like beans, cabbage, corn, onion, pepper, pea, and radish. Large infestations can completely defoliate a lawn in a few days.

      Armyworms are surface feeders and are easily controlled by insecticides when identified early enough. Apply Ortho® Bug B Gon® Insect Killer for Lawns when you find 4 to 5 small, healthy armyworms per square foot of lawn. Under small to moderate infestations, although the grass blades may be chewed, the crowns are not damaged by the feeding and can recover if the damaged area is kept well fed and watered. The most severe damage occurs when armyworms attack during hot, dry weather.

  2. Raquel Narvaez on September 16, 2016 at 7:34 pm

    What fertilizer I should use for St Augustine Palmetto?

    • Harmony Brands on October 28, 2016 at 4:13 pm

      Hi Raquel, You should use Milorganite or any fertilizer with a 10-10-10.