Crabgrass Preventer After Overseeding: A Kansas City Guide

Why can crabgrass preventer be a problem after overseeding?

Crabgrass preventer can be a problem after overseeding because it kills grass seedlings as well as crabgrass seedlings. Crabgrass preventers, also called pre-emergent herbicides, work by killing tiny plants right after they sprout through a treated layer of soil. Most of these products can't tell crabgrass from tall fescue. That's why a lawn overseeded in the fall needs its new grass well-rooted before a preventer goes down, and why spots you plan to reseed need special handling.

Is it safe to use crabgrass preventer on a lawn overseeded last fall?

Yes, in most cases it's safe to use crabgrass preventer the spring after a September overseeding. K-State Research and Extension generally advises waiting until new grass has been mowed at least two to four times, and grass seeded in September usually reaches that point before winter. If you're still caring for newly seeded grass this fall, our guide on what to do after lawn aeration covers watering and mowing.

Take a closer look at your Kansas City lawn if:

• You seeded in October or later.
• Parts of the lawn came in thin or patchy.
• You're not sure how many times the new grass was mowed.

For young fall-seeded grass, K-State notes that dithiopyr (Dimension) can be used the following spring even if the new grass hasn't been mowed yet. Always confirm the label covers your situation.

When should Kansas City homeowners apply crabgrass preventer?

Kansas City homeowners should apply crabgrass preventer around April 15. Crabgrass in Kansas usually starts sprouting around May 1, and a mid-April application gives the product time to spread evenly through the soil first.

The most reliable timing signal is the Eastern redbud tree. Apply when the redbuds in your neighborhood are close to full bloom. This adjusts automatically for early or late springs.

For the best results on an overseeded lawn:

• Water it in: give the lawn at least half an inch of water within three days of applying.
• Don't apply too early: most preventers lose effectiveness after about 60 days.
• Plan a follow-up for short-lasting products: products like pendimethalin typically need a second application six to eight weeks later.
• Use longer-lasting products for flexibility: dithiopyr (Dimension) and prodiamine (Barricade) can give season-long control from one application, applied anywhere from mid-March through mid-April.

What should you do about bare spots you want to seed in spring?

Bare spots you plan to seed in spring should not get a standard crabgrass preventer, because it will likely stop the new grass seed from establishing. Kansas City homeowners with spring bare spots have three practical options:

1. Use a seed-safe preventer on those spots. K-State lists mesotrione (Tenacity) and siduron (Tupersan) as the only preventers safe to apply at seeding time. Use the lowest label rate and expect slightly fewer seedlings. Some starter fertilizers for new grass contain mesotrione, so check the label.
2. Skip the preventer on just those spots. Treat the rest of the lawn as usual.
3. Wait and reseed next September. Spring seedings often struggle because summer weeds like crabgrass compete with young grass. In Kansas City, fall is the better season for seeding tall fescue. Our comparison of the best grass seed for Kansas City lawns can help you choose.

Which crabgrass preventer fits a lawn overseeded last fall?

The right crabgrass preventer for a lawn overseeded last fall depends on how established the new grass is and whether you plan to seed again in spring.

Check that the label matches your grass type. For example, mesotrione is labeled for new tall fescue, Kentucky bluegrass, and perennial ryegrass, but not new fine fescue.

What else helps protect a newly overseeded Kansas City lawn from crabgrass?

Thick, healthy grass is the best long-term protection against crabgrass, and fall overseeding already helps build it. A few spring habits protect that progress:

• Apply preventer before fertilizer. K-State recommends this order. Fertilizing tall fescue in March or early April pushes fast top growth that invites weeds and disease. September and November are the most important feeding times for fescue.
• Watch sidewalk and driveway edges. Crabgrass often appears first in bare soil next to pavement, where the ground warms faster. In thin grass it can show up a few weeks later.
• Note thin areas for next fall. Spots that are still sparse in late spring are good candidates for overseeding again in September.

Fall-to-spring timeline for an overseeded Kansas City lawn

This timeline covers the months between a September overseeding and the end of crabgrass season. For the full year, see our month-by-month fertilizing and aeration schedule for Kansas City.

Frequently asked questions

Does crabgrass come back from last year's plants?+

No. Crabgrass is an annual weed, so each year's crabgrass grows from seed. That's why preventing new seedlings in spring is the main control strategy.

Can crabgrass preventer be applied in the fall for next spring?+

Prodiamine (Barricade) can be applied in the fall to control crabgrass the following spring. It shouldn't be used on areas you just seeded or plan to seed.

Will crabgrass preventer kill crabgrass that's already growing?+

Most crabgrass preventers only stop new seedlings. Dithiopyr (Dimension) is the exception, since it can kill very young crabgrass.

Is a March "weed and feed" a good idea for Kansas City tall fescue?+

Usually not. The fertilizer can push too much early growth, and a March application may wear off before crabgrass finishes sprouting. Mid-April timing works better in Kansas City.