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Growing Green: Crabgrass Prevention in Your Home Lawn

The annual harbinger of spring has arrived…the spring lawn care questions have begun in earnest, specifically, when to start treating for CRABGRASS!!!  If you want to preemptively strike out against this menace, the following information should help in your home lawn defense. 

Crabgrass is a warm-season, annual grass, which grows best in the heat of mid-summer. It overwinters as seed in your lawn, and typically begins to grow around Memorial Day, when the soil temperature reaches about 50 degrees. Crab grass grows close to the ground and is usually lighter in color than desirable lawn grasses.  If you had crabgrass in your lawn last fall, you probably have seed waiting to sprout this spring.

The good news is that there are several measures you can take to prohibit crabgrass from getting a hold in your lawn.   A healthy, relatively dense lawn is your best prevention against invasive, undesirable weeds. Properly fertilizing and watering your lawn will help insure an adequate supply of plant nutrients and water for vigorous grass growth.

  • Adjust your mower height to 2 ½ - 3 inches to provide more shade at the soil surface. Without adequate light, crabgrass seeds (and other lawn weed seeds) will be less likely to germinate.
  • Mow frequently, removing only 1/3 of the blade length each time.
  • Water consistently and thoroughly throughout the growing season. Apply enough water to bring the weekly total to one to one and a half inches of rain and irrigation water combined.
  • Fertilize more heavily in fall than spring.
  • Aerate the lawn in early fall as soon as temperatures cool, if soil is compacted or clay-like.
  • Apply a pre-emergent weed killer.

Pre-emergent herbicides come in either granular or liquid form and kill crabgrass seedlings as they germinate. They act as an invisible shield across the soil surface that stops emerging crabgrass from breaking through. Do not aerate lawns once you have applied a pre-emergent, and never use a pre-emergent on lawns that have been seeded. Apply pre-emergents from late April to late May.  Granular forms are easy to apply with a spreader, and are often mixed with an early summer lawn fertilizer.

For more information on crabgrass prevention and spring lawn care, log on to the University of Minnesota Extension website at

Robin Trott is a Horticulture Educator with University of Minnesota Extension.