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Why Did My Crabgrass Preventer Not Work?

August 1, 2013

This time of year some folks see crabgrass in their lawn even though they put down a preventer last spring.  The question:  “Why didn’t the product work?”

Here is a little crabgrass 101:  Crabgrass weed preventers kill the new plants as they sprout, not before they sprout.  A dormant crabgrass seed can lay in the soil until the conditions are right for growth.  If grass is mowed tall (2-1/2 to 3 inches) and the lawn is thick, crabgrass has a hard time germinating.  If the crabgrass preventer is active when it tries to sprout, the preventer will kill it.  Crabgrass seeds germinate like waves hitting a beach.  The first crabgrass sprouts next to a sidewalk or on a south slope where soil warms first in early spring.  The next crabgrass to germinate is in a thin lawn where the sunlight and warmth helps the seed get started.  The last crabgrass germinates in mid to late summer in newly exposed soil as grass thins from disease or insects or as the soil surface is broken from weeds being pulled exposing crabgrass seeds to the warm surface.

There are several reasons that crabgrass preventers may not work as well as expected:

First, if the granules were spread too light or areas were missed in the lawn, prevention will not last as long as expected.

Second, if the product was put down too late, you may see crabgrass growth near a sidewalk or on a south slope where the soil warmed faster in early spring and the seeds started to sprout before application.

Third, if the soil was disturbed after spreading by aeration, dethatching, or pulling weeds, crabgrass seeds will sprout as they are exposed and the crabgrass barrier is no longer there.

Fourth, the granules will be less effective if the lawn does not receive around a quarter to a half inch of water within 2 to 3 days of application.  If there is heavy rainfall to create flooding and soil movement or if the spring/summer rainfall is significantly above normal, the prevention will not be as strong.

And finally, if your grass was weakened because it was mowed too short, there was drought in late summer or your lawn got a fungus or insect problem that thinned the grass, crabgrass could germinate if the crabgrass preventer was no longer active.  (Crabgrass preventers generally last from 6 weeks to 4 months depending on the product used.  Scotts Halts products last up to 4 months.)

There are two reasons Scotts Halts products work better than other brands.  Halts contains one of the top rated ingredients for preventing crabgrass and the granules are smaller to provide better coverage of each square inch of lawn surface.  Competitive products that do not work as well use larger particles and a lower rated, cheaper ingredient to prevent crabgrass.

Crabgrass germinated in this area where the grass was thinned from a lawn fungus problem.  It is easier to kill before it gets big.

Crabgrass germinated in this area where the grass was thinned from a lawn fungus problem.

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33 Comments
  1. Todd permalink

    Hello,
    I need some advice. I just bought a house and the yard has been neglected for a year. It has about every kind of weed out there, but it has some decent grass as well. I noticed some dead patches and found mole tracks. So I realized I had grubs. Last week I used Grub Ex and hopefully that will fix that. I am planning on aerating and over seeding in Sept. But was wondering if I could use some Turfbuilder with summer guard right now or should I wait? Or should I use something different. I don’t want to use anything for the weeds so I can over seed. I am in Northern Virginia.

    Thank you
    Todd

    • Hi Todd
      First I want to point out that even though you have put down protection against the next generation of grubs, you may still have moles on occasion as their primary diet is earthworms. I think you can skip the Turf Builder SummerGuard application now since GrubEx provides protection against some of the insects controlled by SummerGuard. Based on where you live, fall is the most important time to feed your lawn. Your schedule could look like this: Sept 1: Grass Seed and Starter Lawn Food. A good seed blend for your area is our Heat-Tolerant Blue Blend. Oct 15: Turf Builder Lawn Food. Late Nov: Turf Builder WinterGuard. Once your new grass has been mowed 4 times this fall, you can treat your weeds either with Ortho Weed B Gon MAX plus Crabgrass Killer or Substitute one of our Turf Builder Weed & Feed products for one of your feedings. Good Luck with your lawn.

      • Todd permalink

        Thank you for the great information. I look forward to the coming fall now. So if I am able to mow 4 times before the November feeding I could use Winterguard with weed control instead of Weed B gone MAX? Or is it better to just use winterguard and spray weed B gone?

      • Hi Todd… You may find that you are able to mow 4 times sometime between your second and third feeding. If weeds are wide spread throughout your lawn, the weed & feed would be easier. If your weeds are mainly in certain areas with spray may be a better choice. One other point, the weed list on the Weed B Gon MAX is much more extensive than on the weed and feed. I gave you a 6 week spread between feedings, however you can squeeze that down to 4 weeks in fall.

  2. I have worked so hard to fight crabgrass in my yard for the past 3 years using the various methods you’ve suggested & also even removing portions of the lawn & laying sod in places, but I have 2 conditions that I’ve continued to battle this year: First & foremost – next door neighbors who do nothing with their yard except mow it (low so it doesn’t have to be done as often, I suppose 😦 ); and secondly, a significant amount of rain this year, which I guess kept our prevention diluted (though we did the lawn more than once beginning very early in spring & directly sprayed Ortho on the crabgrass anytime it was spotted). Granted, the good grass looks healthy, no signs of grubs either (as we also use GrubEx) – just a continual battle with Crabgrass that is RESILIENT!!! Because it’s getting late in the summer & I’d like to do some overseeding in the fall, any suggestions for specific action at this point? Thanks!

    • To humanTriumphant… Sorry you have had such an ongoing problem with crabgrass. Let me know where you are located and I can provide some seed blend suggestions if you like. As you know, crabgrass will die with the frost this fall. For many areas of the country, the key to getting the lawn thicker so crabgrass has a more difficult time germinating and to help assist your spring applied preemergent, is to feed at least twice this fall. Lawns grown in some parts of the country even benefit from a third feeding. The other key is mowing so that your final cut is 2 to 1/2 or 3 inches (this recommendation is for most grass types, however I can be more specific once I learn where you are located).

      • Thanks! i’m in Southeast TN

      • Hi humanTriumphant… You are definitely in the area that benefits from three fall feedings: Sept 1, Oct 15, Nov 25. Scotts Heat-Tolerant Blue grass seed blend is a good one for your area. (Our daughter graduated from Univ of Tenn.)

      • Thanks for the great info. I’ve marked the dates on my calendar. 🙂 Long live “Rocky Top” (that goes for our yards around here too – haha!)

  3. Bob permalink

    I put down Scotts fertilizer and weed control. How long after can I mow lawn again? How long does it take after application to kill weeds.

    • You can mow 24 hours after applying. You should start to see weeds fade away over the next several weeks.

  4. Tom permalink

    Ashton is it ok to apply Halts twice one in early spring and then 6 weeks later?

    Will this extend the coverage and help? It seems every year after applying Halts my grass is fine until August… then it appears..

    Thanks

    • Hi Tom… Our Halts products should not be applied more than twice a year and you should allow at least 8 weeks between applications. You may see some extended control with a second application. If your grass is weakened in August, crabgrass can get a toe hold as you have seen.

  5. Rob permalink

    I’m in eastern Massachusetts. I applied Scott’s w/ Halts in the spring as instructed, but as your post alludes I’m getting some serious crabgrass patches now. It’s MUCH better than it was at this time last year, when the entire yard was filled with crabgrass (we’d just bought the house and hadn’t started yard maintenance yet). At this time last year, most of the yard was burned out and dormant; this year, it’s very thick, tall, and green.

    Some of the crabgrass has started to show seeds, and for the most part I’m managing it by pulling it by hand (always careful to get the roots). It’s time consuming, but I don’t want to put down chemicals if I don’t have to. I typically mulch the lawn when I mow, but I’m bagging over the larger crabgrass patches that are showing seeds.

    Is pulling the crabgrass effective, or am I wasting my time? From a year-over-year perspective, I feel like I’m getting somewhere with this lawn, but I’d like to get it to a little-to-no crabgrass state soon!

    • Hi Rob
      What I have seen over the years on lawns that are totally infested with crabgrass is that the first year of putting down a preventer can get you up to around 90% control. Sometimes it takes several years of putting down a preventer to get close to the 100% range. Feeding your lawn regularly so the good grass is thicker and mowing at one of the higher settings so your lawn is 2-1/2 to 3 inches after the cut also helps. The pulling and bagging helps to keep from spreading new seeds for next year. Sometimes when you pull you break the soil surface enough to allow more seeds to germinate. Any plants you do not pull will get killed with the frost this fall.

  6. For various reason’s I am extremely late this year getting to my spring cleanup and fertilizing. I feel I have missed my window of putting crabgrass preventer down. I want to put something down this week so should I skip Crabgrass Preventer and just put down a regular fertilizer, or will putting the preventer down still help (a little)?

    Also, I battle crabgrass every year. What do you recommend I apply or spray to kill the crabgrass that does grow up this summer?

    I am a CT resident.

    • Hi Brian
      Thanks for giving my your location. Crabgrass germinates kind of like waves hitting a beach. The earliest germination will happen next to a sidewalk on a south facing slope where soil warms first. Germination will continue into early summer. So, I suggest you still put down Turf Builder with Halts to prevent some of the later germinating crabgrass. Then between now and early summer if you see some young crabgrass that you missed, you can spray it with Ortho Weed B Gon MAX plus Crabgrass Killer.

  7. David Ortiz permalink

    A professional landscaping company told me to apply Halts in early March and 4 weeks later in April, then apply Scotts Fall weed and feed in the fall. I would like your input. I have Zoysia grass and trying to get rid of crabgrass and other weeds. Thanks

    • Hi David Ortiz
      Typically a single application of Halts in early spring will do a good job of preventing crabgrass. Suggest you put this down ASAP. If your crabgrass problem has been especially difficult to control you can spray any plants that escape past the preventer with Ortho Weed B Gon MAX plus Crabgrass Killer. Here is a link to product info:
      http://www.ortho.com/smg/goprod/ortho-weed-b-gon-max-crabgrass-control/prod70146/
      This product will also control a wide range of weeds in your Zoysia. An early September feeding of Turf Builder WinterGuard Weed & Feed will give your last feeding of the year while controlling fall weeds. To help keep your Zoysia grow thicker to resist new weeds, feed 4 times a year. Scotts Turf Builder or Scotts GreenMAX would be a good choice. Your first feeding will be when you see about 50% of your Zoysia greening up after winter dormancy.

  8. jeff permalink

    hello I’m in NJ been fighting my lawn for 5 yrs now. aerate over seed fertilizer an every thing else. From Scotts to penning products. so it is now august an crab grass took over as well as every other weed again. have fertilized seeded Scotts yellow bag an Scotts tall fescue with fretlizer.this year my ph is 6-7 put down lime last year an over seeded came up awesome in April an now not too good like I said every weed possible . if I put crab grass or weed control preventer now is it worth it or the best time any help thanks’.

    • Hi Jeff
      Your soil pH is good so lime is not necessary now. A crabgrass/weed preventer is not recommended now for the kind of weeds you are dealing with as they are already up and growing. You can spray crabgrass and other weeds now with Ortho Weed B Gon MAX plus Crabgrass Killer. You will be able to seed a month after spraying. Fall seeding will be more successful than spring as there is more time for the grass roots to develop before next summer. The other advantage to fall seeding is next spring you will be able to use a stronger crabgrass preventer than the one you have to use when you are planting grass seed in spring. Put down Scotts Starter Lawn Food if you seed this fall and feed an additional time later in fall with Turf Builder WinterGuard. If you do not seed this fall, feed first with Turf Builder in September and follow up with Turf Builder WinterGuard 6 weeks later

      • jeffrey govito permalink

        So I seed in fall winter guard? Than when to put down crabgrass/weed prevention? Thanks for the quick response.

        On Aug 9, 2016 8:12 AM, “tipsfromashton.wordpress.com” wrote:

        > ashtonritchie commented: “Hi Jeff Your soil pH is good so lime is not > necessary now. A crabgrass/weed preventer is not recommended now for the > kind of weeds you are dealing with as they are already up and growing. You > can spray crabgrass and other weeds now with Ortho Weed B Gon” >

      • Hi Jeffrey govito
        If you seed this fall feed the same day with Scotts Turf Builder Starter Lawn Food for New Grass. Then about 6 weeks later feed with Turf Builder WinterGuard. Next spring around the time of your first mowing feed with Turf Builder with Halts Crabgrass Preventer.

      • jeffrey g permalink

        Have not had any luck with Scott’s products in the last 5 years. I do everything as directed on all type of products. an Scott’s program.i have even installed a irrigation system in. Any other products to recommend thanks again

        On Aug 9, 2016 1:40 PM, “tipsfromashton.wordpress.com” wrote:

        > ashtonritchie commented: “Hi Jeffrey govito If you seed this fall feed the > same day with Scotts Turf Builder Starter Lawn Food for New Grass. Then > about 6 weeks later feed with Turf Builder WinterGuard. Next spring around > the time of your first mowing feed with Turf Builder with” >

      • Hi Jeffrey g
        Sorry I do not have any other recommendations other than Scotts or Ortho products. As I indicated before if you shift from spring seeding to fall you will have a better chance of developing a more vigorous root system prior to next summer and you will be able to use a better crabgrass preventer next spring that has a longer residual than the one that is compatible with spring planted grass seed. One other thought you mentioned earlier that you aerated your lawn. If you did this after putting down a crabgrass preventer in spring, you will typically have a crabgrass problem as the aeration process breaks the weed prevention barrier allowing weed seeds to more easily grow. Hope this extra info helps.

      • jeffrey g permalink

        Thank you. so I’m going to aerate an thatch this fall.seed an us a starter fertilizer witch is the best time date in South Jersey? Than maybe a winner guard? Yes or no an if so how long after the seed? Than a crabgrass prevention? An if so what date an how longafter? Does freezing affect it if done in Feb? Thanks again for your time an help

        On Aug 9, 2016 4:50 PM, “tipsfromashton.wordpress.com” wrote:

        > ashtonritchie commented: “Hi Jeffrey g Sorry I do not have any other > recommendations other than Scotts or Ortho products. As I indicated before > if you shift from spring seeding to fall you will have a better chance of > developing a more vigorous root system prior to next summer an” >

      • Hi Jeffrey g
        In South Jersey you can seed in early September and feed with Scotts Starter Lawn Food the same day. Then follow up with Turf Builder WinterGuard 6 weeks later (Suggest you skip any weed controls this fall so you do not damage your new grass.) Then next March around the time of your first mowing you can put down Turf Builder with Halts Crabgrass Preventer. Good luck with your lawn.

      • jeffrey g permalink

        Thanks again for the help. But how many times do I fertilize/ weed an feed an put crabgrass prevention down in one season if I start September/ October this year. After I aerate an thatch? Thank again

        On Aug 23, 2016 8:46 PM, “tipsfromashton.wordpress.com” wrote:

        > ashtonritchie commented: “Hi Jeffrey g In South Jersey you can seed in > early September and feed with Scotts Starter Lawn Food the same day. Then > follow up with Turf Builder WinterGuard 6 weeks later (Suggest you skip any > weed controls this fall so you do not damage your new grass” >

      • Hi Jeffrey g
        Here is your schedule for South Jersey (giving you a total of 4 feedings over the next 12 months):
        Early Sept: Grass Seed and Starter Lawn Food
        Late Oct: Turf Builder WinterGuard (once your new grass seedlings have been mowed 4 times, you could put down WinterGuard Weed & Feed instead, or spray any weeds with Ortho Weed B Gon MAX… but make sure your new grass has grown enough to be mowed 4 times)
        March (around the time of your first mowing): Turf Builder with Halts Crabgrass Preventer
        May: Turf Builder Weed & Feed and GrubEX

      • jeffrey g permalink

        They have a fertilizer for new grass an grab grass prevention from Scott’s? About to lay seed lime. What is you thoughts on the fertilizer? Should I just us starter fertilizer for new grass. Thanks

  9. Mike permalink

    Long Island NY April 17 Laid down the Scotts yesterday, today rain is puddling on grass. How much will this affect its effectiveness ?

    • Hi Mike
      As long as you are not seeing granules being washed away because of a heavy slope in your lawn, I believe you will still get the results expected.

  10. Mike permalink

    Thanks. Had a light rain first , so the granules were already melted.

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