Relying on chemical crabgrass preventer is just one strategy homeowners can employ to reduce the potential of crabgrass in the home lawn. Crabgrass preventers also will prevent other annual grassy weeds, like the foxtails, and a few broadleaved weeds, like annual chickweed. These products are reliable and will do the job as advertised, as long as the products are applied in a timely manner.
Crabgrass will germinate in the spring as soon as the soils warm consistently to the 55 to 60-degree range for a 7 to 10 day period. This spring, this has not been easy to figure out. Some of our usual indicator plants are not helping us this year either, and a soil thermometer always provides a more accurate picture. A crabgrass preventer will need to be applied early enough to catch the crabgrass seed as it begins to germinate. If put on too late, you still get some control though, because crabgrass seed will continue to germinate as temperatures climb into the 90s. However, the earliest of the seed will have had the opportunity germinate and show up in the lawn.
One of the best cultural practices you can do this year, and every year in the future, is mow more often while the lawn goes through the natural spring flush. Frequent mowing does not stress the grass plant as you are only removing a small portion of the grass blade, keeping it competitive with any weeds. The goal is to remove no more than 1/3 of the grass blade at any mowing. While the lawn flushes out in the spring, mowing may need to be done every 3 to 5 days to maintain the 1/3 rule. If the lawn is fertilized with synthetic fertilizer during the already natural growth flush, adjust the mowing frequency as needed. A better fertilizer timing would be to allow the natural flush to slow down and then apply it. Lawns being fertilized organically will not see that extra amount of rapid growth and have a sustained spring greening. A key part of the increased mowing strategy is to be sure your mower blade is sharp. It should be sharp not only start the season, but kept sharp all season long. Your lawn will look better, and the mower will not work as hard, reducing the hydrocarbons in the environment.
Crabgrass is opportunistic; all that is needed is a bit of open space in the lawn to get started. Additional cultural practices can include topdressing and reseeding if the open spaces are more than about 4 inches across. Existing grass plants can usually fill in smaller areas during the growing season.
To help promote your lawn grasses over crabgrass and other weeds, encourage deep roots. Without any outside influences, soils do compact over time, so providing a core aeration will easily promote better water infiltration, soil air into the profile and encourage those deeper grass roots.
If you can promote a better lawn this season, crabgrass seeds will not have the same opportunities to germinate in 2019.
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.