Lawn got you crabby? Time nears to apply preventers
K-State horticulture expert explains best practices for treating crabgrass
At a glance: Applying herbicide in April can help to prevent crabgrass problems in home lawns, said K-State horticulture expert Matt McKernan.
More information: Matt McKernan, hortsupport@ksu.edu
Related: K-State Horticulture Newsletter | Weed Control in Home Lawns | Planting a Home Lawn | Fertilizing Kansas Lawns
March 12, 2026
K-State Extension news service
MANHATTAN, Kan. — A weed commonly found in Kansas lawns can sure make homeowners feel pretty crabby this time of year.
But applying an herbicide at the right time can help alleviate crabgrass problems, said Kansas State University horticulture expert Matt McKernan.
“For most of Kansas, crabgrass typically begins to germinate around May 1,” McKernan said. “April 15 is normally a good target date for applying crabgrass preventer because it gives active ingredients time to evenly disperse in the soil before germination starts.”
Crabgrass preventers are another name for pre-emergence herbicides that prevent crabgrass seeds from developing into mature plants. “They do not kill the weed seed or even keep the seed from germinating, but rather kill the young plant after it germinates,” McKernan said.
He added that most crabgrass preventers have no effect on existing plants, “so they must be applied before germination.”
“Preventers do not last forever once applied to the soil. Microorganisms and natural processes begin to gradually break them down soon after they are applied. If some products are applied too early, they may have lost much of their strength by the time they are needed.”
McKernan said most crabgrass preventers are fairly ineffective after 60 days, although there are options for products with longer control.
“Work with your local extension office to decide which pre-emergence is right for you and determine when it should be applied,” he said. “Weather conditions vary every spring in Kansas, so using a calendar date to time applications is not a perfect solution.
"Another technique for properly timing applications is to apply a crabgrass preventer during the same time that the Eastern Redbud tree – known for its pretty purplish-pink flowers -- is in full bloom. This indicator, along with soil temperatures and other tools can help you maximize the effectiveness of your weed preventers.”
“We recommend homeowners apply crabgrass preventers before fertilizer so the grass isn’t encouraged to put on too much growth too early,or be more prone to disease mid-summer,” McKernan said. “However, it may be difficult to find pre-emergent products without fertilizer, so choose the pre-emergent with the lowest percentage of fertilizer included.”
McKernan and his colleagues in K-State’s Department of Horticulture and Natural Resources produce a weekly Horticulture Newsletter with tips for maintaining home landscapes and gardens.
Interested persons can subscribe to the newsletter, as well as send their garden and yard-related questions to hortsupport@ksu.edu, or contact your local K-State Extension office.
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K‑State Extension is a short name for the Kansas State University Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the wellbeing of Kansans. Supported by county, state, federal and private funds, the program has county extension offices statewide. Its headquarters is on the K‑State campus in Manhattan. For more information, visit www.ksre.ksu.edu. K-State Extension is an equal opportunity provider and employer.