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When to Spread Crabgrass Preventer (a Preemergent Herbicide)

Posted By Fred On October 11, 2011 @ 7:00 am In Outdoor | 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 [1] 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 [2] 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 [3] 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 [4] and to spread seed.
  • Wait 2 months before applying other chemicals like weed and feed [5] 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 [6], and this detailed guide about weed control [7] 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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URLs in this post:

[1] great picture of crabgrass here: http://images.google.com/imgres?imgurl=http://alfalfa.okstate.edu/weeds/sumanngrass/crabgrass/sm-crabgrass-074.jpg&imgrefurl=http://alfalfa.okstate.edu/weeds/sumanngrass/crabgrass/sm-crabgrass-074.htm&usg=__xPtDwiS1mrqD3fKLapGMKZNEGqc=&h=475&w=482&sz=51&hl=en&start=2&um=1&tbnid=ZUNnBc1AD7XBsM:&tbnh=127&tbnw=129&prev=/images%3Fq%3Dcrabgrass%26hl%3Den%26sa%3DX%26um%3D1

[2] applying the preemergent: http://www.oneprojectcloser.com/apply-crabgrass-preventer-in-the-early-spring/

[3] Watering your lawn: http://www.oneprojectcloser.com/watering-your-lawn/

[4] aerate your lawn: http://www.oneprojectcloser.com/aerating-your-lawn/

[5] weed and feed: http://www.oneprojectcloser.com/when-and-how-to-apply-weed-feed/

[6] Scott’s Turfbuilder with PLUS 2 Weed Control: http://www.oneprojectcloser.com/weed-and-feed-review-scotts-turfbuilder-with-plus-2-weed-control/

[7] weed control: http://www.oneprojectcloser.com/lawn-weed-control/

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