When to Spread Crabgrass Preventer (a Preemergent Herbicide)
Crabgrass is one of the most common annual grass weeds in North America–and one that is particularly common here in our little subdivision of Baltimore County, MD. Crabgrass grows from a single seed and shoots out wide blades of grass in the shape of a star. The plant grows very rapidly, moving from seedling to full plant in 14 days. OK State University has a great picture of crabgrass here if you’re looking to identify it.
The term annual grass weeds refers to the whole set of weeds that occur annually in lawns. These weeds germinate in the soil in early Spring/Summer, grow, spread, and drop seeds during hot Summer weather, and die off in the frosts of early Winter. Each year, no living crabgrass remains in the lawn, only ungerminated seeds lying on the surface and just beneath the surface of the soil.
How to Control Crabgrass
Nature gives us a short window to stop crabgrass before it starts. In early Spring, before the new seeds germinate, a preemergent herbicide can be applied to the soil. Preemergent herbicides (called preemergents for short) prevent crabgrass seeds from germinating into the full plants. The result: less crabgrass grows during the season. And, since less crabgrass grows, there are fewer plants dropping seeds for the next cycle. With consistent application of preemergents, along with other grass care, crabgrass can be virtually eliminated from a lawn. This gives way for the healthy, rich turf we all dream of.
When to Apply Crabgrass Preventer
Crabgrass seeds germinate in the early Spring when the temperature of the surface soil rises into the 50s and 60s. Once the seeds germinate, the opportunity for prevention is passed. So, applying the preemergent early is key. Scotts Turfbuilder with Halts Crabgrass Preventer (our preemergent of choice this year because that’s what was available at the big box) recommends spreading the preemergent before the days are regularly in the 80s. We think that’s much too late. Once the days are regularly in the 60s and 70s, the seeds will be germinating and sprouting small plants. Instead, apply preemergents very early in the season, while the temperatures are still in the 50s. In Baltimore County, MD, this means spreading the preventer before April 1.
Scotts crabgrass preventer can be applied only twice per year, once in the early Spring and again in the late Summer if desired. The limitation has more to do with the Turfbuilder nutrients in the product rather than the crabgrass preventer. A product that only contains the herbicide could be applied more frequently. That said, we think it makes sense to spread preemergent only in the early Spring, while focusing on building up the cultured turf for the rest of the year.
Don’t Plant Grass Seed | Avoid Garden Areas
Because preemergents prevent seed germination, they should be carefully applied so as to avoid garden and other new growth areas. You should also avoid planting any type of grass seed within 3-6 months after applying preemergent. In other words, plan to plant new turf only in the Autumn.
Other Considerations / Instructions
- Always follow instructions on the crabgrass preventer you choose.
- Don’t aerate or heavily rake the lawn after applying pre-emergent. (This will degrade the barrier). Wait for the Fall to aerate (see Todd’s article on how to aerate a lawn for that) and to spread seed.
- Wait 2 months before applying other chemicals unless you are following instructions or consulting with a professional.
Stay Tuned for the Scotts Turbuilder & Crabgrass Preventer Review
We took some pictures of the lawn just before we applied Scotts’ product. We’ll be writing an update to this post in the early Summer. If you aren’t already subscribed, grab our feed by clicking one of the subscription buttons in the upper right. You’ll receive great articles by e-mail, including this upcoming review!
What do you think? Do you spread crabgrass preemergent each year? Tell us about your results in the comments…
Comments & Conversation on this Article...
11 Responses to When to Spread Crabgrass Preventer (a Preemergent Herbicide)
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March 23rd, 2009 10:26 pm
Great post Fred! Very timely, I live in the North East and was just thinking how I need to get ready to apply a Crab Grass pre-emergent as well. Last year my lawn looked good and hopefully there will not be much Crab Grass again this year. I have been working very hard over the last few years to really keep my lawn in tip top shape and cannot overemphasize the importance of eliminating Crab Grass before it germinates.
Also, I am very interested in seeing how you do with the Scotts product. I have been using the Jonathan Green.
Excellent information, Thanks!
March 29th, 2009 11:18 am
Does anyone know when I should apply crabgrass preventer in upstate NY? I wanted to try Greenview seedstarter and crabgrass preventer as it lets you overseed and helps prevent crabgrass. Should I wait till temps are in the mid 50 to 60’s before I apply? Thanks.
March 29th, 2009 5:48 pm
David, I wouldn’t wait that long … once the temperatures are out of the freezing zone and Spring is approaching, I would apply the preventer. Likely no later than 4/15 (which would be too late by MD standards).
I’m surprised that a crabgrass preventer encourages overseeding, as most pre-emergents would prevent new grass seed from germinating.
March 29th, 2009 6:08 pm
Both Greenview as well as Scotts has starter fertilizer with crab grass preventer. They are expensive and they don’t last as long as the typical crab grass preventers but if you have bare spots you have to pick your poison. Do you think if I seeded in a couple weeks the seed would die before the temperatures raised enough for germination to take place? I’ve heard the seed will rot if you plant it too soon? I’m not sure what too soon is in central NY?
March 30th, 2009 12:07 pm
Hi Fred, thanks for your post on this topic – I just recently spread the same on my lawn — unfortunately I didn’t read carefully the package and also spread on top soil which I hope to put new seed on in the coming weeks (i.e. within 1 month of putting the pre-emergence down). Any ideas about what I can do? This is over 3,000 sqft on our front and back lawn! Would agitating the soil a lot (scooping and flipping with a shovel, raking) help? It already rained and the fertilizer is not recoverable. I would like to seed v. sod, but would sod be an option in your opinion? I’m in NY State (90 min north of NYC) looking to put Tall Fiscue (90%+) with some Rye and Kentuck Blue (10%). Thanks for any thoughts!
March 31st, 2009 12:08 am
Dave, Unfortunately, I’ve not run into this situation. The crabgrass preventer won’t have a negative impact on sod (as its already got a mature root system). As for whether you can turn the soil enough to eliminate the pre-emergent, I’m not sure. If you must do it, I would suggest turning the dirt and watering it a few times to try to get the chemical to seep further down. Worst case scenario is you get some bare spots and you work to fill them in over the Summer / Fall / next year. Seed is going to be significantly cheaper than sod, so I understand the appeal.
March 31st, 2009 9:42 am
Fred – Thanks for your thoughts. We may sod certain sections and be patient with the rest!!
April 13th, 2009 12:14 pm
As a follow up for anyone interested – I called the phone number on the bag (the Scott’s fertilizer bag Fred highlighted) and the representative suggested that we made the right choice b/c crabgrass would have likely choked growth of new grass. I was advised to wait 6 weeks (from the time of application) for the crabgrass preventer to be absorbed and flushed through the soil. After this time, they recommended we seed the top soil and over seed the rest of the lawn (as desired) and then to apply the yellow bag (plus 2 weed control) to the whole yard after the new grass has been mowed 3-4 times (at least another 4 weeks).
June 12th, 2009 7:51 am
Hi,
I was wondering what is the best way to control crabgrass after it has emerged? I have some new beds which are now empty except for crabgrass. I also have a large area (where a magnolia tree used to be) that I am trying to get zoysia to take. I planted some plugs that are doing OK however they are being swamped by the crabgrass too. Can I spray the crabgrass now and then put in my plants (and more zoysia) in the fall? Thanks for any help!
Charles
June 13th, 2009 10:22 pm
CP-Good question.
You can pull up the crabgrass by the roots and then spread a pre-emergent to prevent further seed germination, but any roots that aren’t completely removed may sprout new leaves and spread, and the zoysia will not germinate new seeds.
I’m not too familiar with zoysia plugs but I would assume they aren’t seeds, but rather zoysia with roots already growing – so the preemergent probably wouldn’t affect them but may take care of your crabgrass preventer.
August 27th, 2009 12:45 pm
I live on the Cumberland Plateau in TN, one hr south of KY. My question is can I top dress my yard and reseed this fall and then spread Crabgrass preventive in the spring and not have it effect the new grass seed?
Based on where I reside when would be the proper time to apply the Crabgrass preventive in the spring?
Thanks,
Dennis