People ask me every spring when they should put down crabgrass preventer. It's a harder question than it sounds, because in central Kansas the answer changes depending on the year.
You've probably heard the old rule: apply before the redbud trees bloom. That's not bad advice — redbuds bloom pinkish-purple in early spring and they're native to Kansas, so they track the weather better than a calendar date does. But honestly, I've always thought that timing is a little on the late side. If you have a spot on the south side of a brick building, the soil there can warm up and start germinating crabgrass well before the redbuds open. A more reliable target is right around the time you mow your lawn for the first time in spring — usually somewhere in mid-March in the Hutchinson and Harvey County area.
The Two Main Products: Barricade vs. Dimension
There are two active ingredients that cover most crabgrass preventers on the market. You'll see a lot of brand names, but they all come back to one of these two:
Barricade (prodiamine) is the longer-lasting option and is generally considered the stronger choice. It's strictly a pre-emergent — it works by stopping crabgrass before it ever germinates. If you apply it at the right time, Barricade gives you solid season-long protection. This is what we use in our program.
Dimension (dithiopyr) is a good option if you've missed the window. It works as a pre-emergent but also kills very small, newly germinated crabgrass that Barricade can't touch. So if you're not sure whether you're too late, Dimension is your safety net. The tradeoff is it doesn't hold up quite as well later in the summer when pre-emergents start to wear thin.
Don't Overseed in Spring if You're Also Treating for Crabgrass
This is where a lot of homeowners get into trouble. Crabgrass preventer doesn't know the difference between crabgrass seed and your good grass seed — it stops all of it from germinating. If you're planning to overseed thin spots, you can't treat for crabgrass at the same time. And if you apply preventer first and then try to seed, you'll need to wait 6 to 8 weeks before that seed has any chance of taking. By then, crabgrass will already have germinated.
If your lawn has thin spots that need seed, the better move is to skip the preventer in spring, reseed in the fall after the heat breaks, and plan to treat aggressively for crabgrass the following spring.
Central Kansas Timing at a Glance
| Timing | What to Do |
|---|---|
| Early–mid March | First mow of the year — ideal window to apply Barricade |
| Redbud bloom | Acceptable timing for short-residual products — borderline late for Barricade |
| After redbud | Switch to Dimension — it can still catch early-germinating crabgrass |
| Late April+ | Pre-emergents won't help — crabgrass is already up |
What if You Miss the Window Entirely?
If crabgrass is already visible and growing, pre-emergents won't do anything. Your options at that point are spot-treating with a post-emergent (which works best on young plants, not established ones) or waiting it out. Crabgrass is an annual — it dies with the first frost. The real goal then becomes not letting it go to seed, which would reload your soil for next year.
The lawns we've maintained for years rarely have serious crabgrass problems, because the consistent pre-emergent applications eventually exhaust what's in the soil. It takes a few seasons, but it works.
Don't Want to Think About It?
That's what we're here for. Our 5-step program includes crabgrass prevention timed for central Kansas conditions — applied when the timing is actually right, not on a fixed calendar date.