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When to Spread Crabgrass Preventer (a Preemergent Herbicide)

When to Spread Crabgrass Preventer (a Preemergent Herbicide)

by Fred Fauth (email Fred) | | October 11, 2011 | 42 Comments »

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.

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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.

Scotts Crabgrass Preemergent (Preventer) and Spreader

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.
  • Watering your lawn after applying crabgrass preventer will help form a protective barrier.
  • Don’t aerate or heavily rake the lawn after applying pre-emergent.   (This will degrade the barrier).  Wait for the Fall to aerate your lawn and to spread seed.
  • Wait 2 months before applying other chemicals like weed and feed unless you are following instructions or consulting with a professional.

More Info

This article covers the application of preemergent herbicide. If you’d like to learn more about lawn care, consider further reading like our review of Scott’s Turfbuilder with PLUS 2 Weed Control, and this detailed guide about weed control and how to target specific weeds.

What do you think? Do you spread crabgrass preemergent each year?  Tell us about your results in the comments…

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Conversation on This Article

42 Responses to When to Spread Crabgrass Preventer (a Preemergent Herbicide)

  • Onlinehandyman responds...
    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!

    [Reply]

  • David responds...
    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.

    [Reply]

  • Fred responds...
    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.

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  • David responds...
    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?

    [Reply]

  • Dave responds...
    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!

    [Reply]

  • Fred responds...
    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.

    [Reply]

  • Dave responds...
    March 31st, 2009 9:42 am

    Fred – Thanks for your thoughts. We may sod certain sections and be patient with the rest!!

    [Reply]

  • Dave responds...
    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).

    [Reply]

  • CP responds...
    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

    [Reply]

  • Fred responds...
    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.

    [Reply]

  • Dennis Tryon responds...
    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

    [Reply]

  • omt responds...
    April 3rd, 2010 8:07 am

    What are the requirements when you apply crabgrass preventer for the following?
    1) Temperature – at the time and for next 24 hours
    2) Before and after application weather condition – 24 hours
    3) Before and after water application to the lawn. – Whether lawn should be watered before or when after application
    4) Best time of the day to apply. The morning when there is dew or any time
    Thanks

    [Reply]

  • Fran responds...
    April 11th, 2010 4:17 pm

    I am in line with omt above. I would like the same questions answered as well as I am in Central New York, and it was extremely warmer than usual the past couple weeks, with 2 days hitting the 80′s. Presently though, it is 59 degrees, and it should remain so, for the next couple weeks. Can you tell me if I should bother with crabgrass pre-emergent? I don’t want to waste my money if those 80 days gave possibilities to the germination of crabgrass. Thank you……Fran

    [Reply]

  • When and How to Apply Weed & Feed on One Project Closer responds...
    February 23rd, 2011 7:01 am

    [...] to-do list. One of those items was to spread weed & feed on my lawn. I missed the window to spread preemergent crabgrass preventer (even though Fred wrote a great post about it). I’m fortunate that I don’t have a ton [...]

  • bill responds...
    March 12th, 2011 6:59 pm

    I am having a very difficult time getting rid of crabgrass in my lawn and garden. Every year it gets worse. I apply preemergent crabgrass preventer just as forsythia breaks into bloom, before the flowers are fully in bloom. Obviously this is not working, I have been relucent to apply too early so as not to disturb the barrier. With this info, any suggestions? I live in northern Balto. Co.
    Thanks,
    Bill

    [Reply]

  • Fred responds...
    March 12th, 2011 11:09 pm

    Bill, you’re real close to us!

    Have you ever tested your soil? That’s the first place to start. If I had to guess, I’d bet that with where you’re located, you’ve got acidic soil. That is likely preventing the good grass from taking root and its allowing the suns rays to get down to crabgrass seeds. Pre-emergent only works over the long run if the natural grass can fill in the spots.

    Get the soil test kit. If it is indeed acidic soil, you’ll want to spread a yard lime and probably aerate. Get the soil to a good PH, then try the pre-emergent again once you’ve gotten that fixed.

    [Reply]

  • Victor responds...
    March 23rd, 2011 1:08 pm

    Would I have a crabgrass problem if I laid the pre-emergent too early in the season? I live in Long Island, NY and I just put it down Mid-March. Would I need to lay a second coating down and if so when should this be done.

    Thanks

    [Reply]

  • Dana Randall responds...
    March 28th, 2011 1:36 pm

    Hello, I live in central Ohio. I have a close to one year old yard. We hydro-seeded our new yard with fescue, rye and KY Blue Grass in mid May before the dry summer. Most took well except the south side of the house and in the back facing the east. We watered throughout the summer. We also got hit hard with crabgrass. Because of the clay soil we did put another application of top soil and over seeded again in Aug and late September. Some of the Aug seed took, none of the September seed. Here it is early spring, temps avg. 45-55 degrees in the days. My delimma is to use Turf Builder now with Halt to prevent crabgrass and wait 6 weeks to plant more seed or seed now and skip the crabgrass preventer? Also if I do any of the above crabgrass preventer and or plant seed, is it ok to areate this spring? Thanks for the advise.
    Dana

    [Reply]

  • Fred responds...
    April 3rd, 2011 9:14 am

    Dana,

    Tough call… the best defense against crabgrass is a strong, healthy lawn. My gut tells me to aerate and seed now, water it so you get germination, and then potentially apply the crabgrass preventer 3-4 weeks later to try to grab some of the crabgrass ahead of the full late Spring, early Summer growing season.

    Fred

    [Reply]

  • [...] achieved by putting down a pre-emergent that forms a protective barrier. Just make sure you spread pre-emergent early enough that seeds have not already started to take [...]

  • Ben responds...
    August 23rd, 2011 11:46 pm

    I’m in Asbury Park, NJ on the Jersey Shore. My lawn is made up of approximately 80% crabgrass and I have to admit, I’ve done nothing to stop it this year because money has been tight. Now I want to get started again. From the articles that I’m reading here, i should forget about the crabgrass that is there now but once it dies off for the season, I should aerate, add lime, seed, and water. The next thing to to is to make sure I get the crabgrass preemergent down on time next spring. After a few seasons, I should start to see less and less crabgrass and more and more “good” grass. How am I doing so far? Also, does anyone recommend one fertilizer over another? How about pre-emergents? Thanks for everyone’s help.

    [Reply]

    Fred Reply:

    Ben, you’re right on. We’ve used Halts crabgrass preemergent successfully, and have been happy with the Scotts line of fertilizing products… But we could be swayed, it’s just worked for us here in MD.

    [Reply]

  • paintergal responds...
    October 11th, 2011 9:16 am

    Our most annoying lawn weed is creeping Charlie. Any tips on getting rid of that?

    [Reply]

    jeff_williams Reply:

    Fall is your best time to attack CC. It is weakest right now. If you hit it now you will have much less in the spring and then hit it again. Depending on how much you have it might take a couple seasons.

    [Reply]

  • Home Improvement CT responds...
    October 12th, 2011 12:13 pm

    Great article , i have a relative who lives in Baltimore County , he always complains of this Crabgrass , i will send him this article , it will be so useful. Thanks for sharing

    [Reply]

  • MissFixIt responds...
    October 12th, 2011 11:28 pm

    We have two circles of “grass” that are in our front lawn they grow way faster then the real grass. Is this crab grass? Is it known to grow in circular patches? I was thinking of cutting it out and removing it with the roots and just reseeding the lawn there.

    [Reply]

    Fred @ One Project Closer Reply:

    Could be… can you send a picture over? There are other kinds of lawn grass weeds that also grow quicker. If you search our site for “grass weeds” you’ll find an article helping you to identify it!

    [Reply]

    MissFixIt Reply:

    I will have to take a picture in the spring/summer when the grass is parched, now that the lawn is green from all the rain colder weather it will be hard to show :( I’ll search your site though thank you Fred.

    [Reply]

  • JustME responds...
    October 17th, 2011 11:50 pm

    Though I’m sure my hubby knows all this, he’s been to greenskeeper school and used to run a 27 hole golf course, I found it all very interesting. I should pay more attention to what he does to our lawn in the future. Thanks for such good and easy to understand information for an average person. I appreciate it.

    [Reply]

  • LP responds...
    November 7th, 2011 2:36 am

    I appreciate this informative article! I’ve saved it for review again this coming Spring. I’ve never really understood about all the different applications that can be made to our yard, which is why it looks so bad. lol I appreciate the explanations. I’m looking forward to doing something about it. Crabgrass is really hard to get rid of, maybe now I can. Thanks!

    [Reply]

  • Tom Evans responds...
    January 30th, 2012 11:15 pm

    I have heard that here in Oklahoma that the preemergence applied last year in combination with our record cold & heat done a number on the bermuda grass, that this year do not apply an preemergence. apply a post-emergence after the bermuda grass comes back good. I heard the preemergence done something to the root system. Any truth to this?

    [Reply]

    Fred Reply:

    Could be… Depends on how Bermuda grass repopulates… Does it drop seeds or just go dormant? Pre-emergent stops seeds from germinating, but it normally shouldn’t kill regular grass (that I know of).

    [Reply]

  • Lois Germond responds...
    February 5th, 2012 1:01 pm

    Will Scotts Super Turf Builder with Halts Crabgrass Preventer prevent germination of other weed seeds – particularly spurge?

    [Reply]

    Fred Reply:

    Lois, I’m not sure if effectiveness on this type of weed. I will say that I’m fairly certain this product prevents all seed germination.

    [Reply]

    Steve Reply:

    I fought a losing battle with spotted spurge for several years – it got worse every year in spite of trying various ways to control it. Last year I finally found a pre-emergent that was virtually 100% effective at preventing it: Green Light Portrait Broadleaf Weed Preventer. It specifically lists spurge as a controlled weed and performs as advertised. If you have a long growing season you need to re-apply after 4-months because there will be seeds just waiting for it to lose its effectiveness! Although their website listed several distributers here in Phoenix I went to all of them and they didn’t have it and sold me something else that simply did not work (eventually ordered it and had it sent from a distributer in Texas). Good luck!

    [Reply]

  • Narinnee Ung responds...
    February 28th, 2012 5:24 pm

    I live in Northern VA, have worked on my lawn to stop the weeds and crabgrass, but it seems nothing is working. I now have about 80% of my lawn covered with crabgrass, and no good grass left in those areas. I just spread Scotts with crabgrass preemergent preventer last week on 2/16, and plan to overseed in April. What would be the best way to bring my lawn back to life ? I will very much appreciate your advice. Thanks !

    [Reply]

    Fred Reply:

    Hi Narinnee,

    I can understand your frustration. Here’s some thoughts:

    1) I think you’re just a tad early applying pre-emergent. I usually like to wait until the first week of spring. It has been warmer here, tho, so it’s hard to be sure.

    2) If the pre-emergent is doing its job well, over-seeding in April should really not work. The pre-emergent should be preventing germination. I usually advise aerating and seeding in the Fall.

    3) In really bad situations, I would recommend pre-emergent twice. Once in the spring (done for you) and again in the June time-frame, as some of it will have washed away. Read directions on your pre-emergent bag, tho, so you don’t over-apply the chemical.

    Good luck. Getting rid of crab grass is a long process, unfortunately.

    [Reply]

    Narinnee Ung Reply:

    Hi Fred,
    Thank you for your thoughts and recommendations. I just hope the pre-emergent I spread in February will work because of the warm weather in the 50-60′s we have had lately.
    I will try the pre-emergent and the weeds control again in June, and do the overseeding in Fall as you recommended. I saw a new product at Lowe’s, Spectracide for crab grass pre-emergent and weeds, that I think about trying. It’s pretty expansive though. But I am concerned that crab grass and weeds will keep coming up in the bare areas.

    [Reply]

  • Icarus responds...
    March 17th, 2013 9:38 pm

    Lots of good information to process

    [Reply]

  • ron responds...
    August 15th, 2013 9:56 pm

    I have reestablished my 401-K drought stricken turf last fall & this spring foregoing any crabgrass premergence, Can I use my previously purchased Scotts spring premergence this Fall inlieu of the recommended Scotts Halts Fall product & expect favorable results ?

    [Reply]

  • mark responds...
    April 25th, 2014 4:47 pm

    Crabgrass needs a soil temp of 57-64 f for 3 days to germinate.Every year is different so to give a date is not wise.If applied to early and with plenty of rain you will not be happy with the results.The best way to determine when to apply a pre emergent is to look for the forsythia to bloom.Forsythia need 55 degree soil temps to germinate no matter where you live.Beyond that you could use a thermometer.

    [Reply]

  • H ball responds...
    May 22nd, 2014 8:10 am

    My landscaper used a pre emergent UNDER Bermuda sod before it was installed. What can I expect? Will growth of sod be reduced?

    [Reply]





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