Get Rid of Crabgrass

Crabgrass is a nasty and prevalent kind of weed that loves full sun and high temperatures. Crabgrass is an annual that dies at the end of the year, but acts like a perennial, spreading thousands of seeds that begin growing the next spring. This process can continue year after year if left untreated. Getting rid of crabgrass won't happen quickly. However, with prevention, extermination, and proper lawn care, you can reclaim your garden from these industrious invaders.

Steps

Preventing Crabgrass with Herbicides

  1. Prevent crabgrass from growing in the first place with pre-emergent herbicides. Pre-emergent herbicides act by forming a chemical layer at the surface of the soil.[1] As crabgrass seeds germinate, they take in the herbicide, which prevents them from sprouting and ultimately kills them.
  2. Apply pre-emergent herbicides in the late winter/early spring when soil temperatures stabilize at 55°F at a depth of 4". This should coincide with the blooming of the forsythia. Buy an inexpensive soil thermometer if you don't know when to time your herbicide application.
    • Always apply the herbicide along with a starter fertilizer. Fertilizer helps thicken the turf, which in turn snuffs out crabgrass seeds that weren't killed by the fertilizer. Apply a starter fertilizer along with your herbicide and your getting more bang for your buck.
  3. When using herbicides, be sure to read the label carefully. As small as the print is, you will find valuable information on time of application and safety precautions. Look for herbicides that use the following active ingredients: dithiopyr, prodiamine or pendimethalin.
  4. Reseed or use the herbicide, but never both. The herbicide that you use to snuff out unwanted crabgrass is the same stuff that will lay waste to the soft, pretty grass you actually want to cultivate. That means you have to seed during one season and use herbicide during another: Seed during the early fall and use herbicide during the spring, making sure to keep a buffer of at least 50 days in between.
  5. Apply post emergent herbicides in the summer, if you see crabgrass. These will kill your grass as well so only use if you have more crabgrass than lawn or thick patches of it.

Killing the Crabgrass

  1. Pick the crabgrass when they're still young. Crabgrass spreads quickly. If you let it grow for a whole season, or if you miss a particular area, you could find yourself with an infestation. Whenever you see a bit of crabgrass, simply pluck it out by hand.
    • Picking crabgrass at a young age is effective at reigning the total population in. Young crabgrass has only two to four stalks and is showing no splayed head.
    • If plucking, water the area with the crabgrass thoroughly beforehand. This loosens up the soil and increases your chances of pulling out all the root systems when plucking. Alternatively, you can also use a pair of pliers to grab and gently pull up the crabgrass.[2]
  2. Mulch your soil after plucking. Mulching after removing the crabgrass by hand gives you a better shot at preventing the crabgrass roots from taking seed and growing willy-nilly all over again. What you're doing is creating another barrier that the crabgrass needs to break through.
    • Areas left thin and spotty after pulling up the crabgrass can be re-seeded in the mulch by using seeds that match your current type of grass or turf.
  3. Resist picking mature crabgrass. Mature crabgrass has splayed seed heads with dozens, if not hundreds of seeds. Picking this crabgrass creates a divot in your lawn into which as many as 5,000 seeds — coming from a single plant — can fall.
    • Instead of picking mature crabgrass, spray it or let it die naturally in the fall. Then cover the area with pre-emergent herbicide in the spring to keep the seeds from sprouting.
  4. Spray postemergence herbicide on larger patches of crabgrass that have not yet gone to seed. Postemergence herbicide takes about 2 weeks to fully work, which is roughly the same amount of time it can take for a seeding crabgrass plant to drop its seeds, nullifying the effect of the herbicide.
    • Apply postemergence herbicide on a warm day with little or no wind.
    • For best results, use the herbicide when the soil is damp but the crabgrass itself is dry. Water the area thoroughly in the late morning and wait until afternoon to spray. Apply moderately in two spread-out application to avoid hurting your turf.
    • Get prepared to spray at least two rounds of herbicide — per instruction, of course — unless the crabgrass is very young.

Using Proper Lawn Maintenance to Weed Out Crabgrass

  1. Let your lawn gulp, not sip. Give your lawn a thorough watering about once a week — a big, nice gulp. This gulp, as opposed to frequent sips, will promote a more robust root system as well as one that's more heat tolerant.
  2. Mow your lawn at least weekly. Frequent (semiweekly) mowing cuts down as much as 80% of weed growth across all species.[3] If you don't have the time to mow twice a week, mow once a week and leave the trimmings over the lawn to act as fertilizer. The trimmings will make it harder for crabgrass to sprout.
    • If there are areas where the crab grass is laying down, use a rake to pull it be before mowing. This helps remove immature seed heads.
  3. Use fertilizers without too much nitrogen in them. "Quick-up" fertilizers are a temporary solution; they'll get your lawn growing nice and green in the short term, but in the long term they actually deprive your lawn of nutrients, making the entrance for crabgrass easier. Use only about 2 to 4 pounds of nitrogen per 1,000 sq feet of lawn, depending on your lawn.[4]
  4. Aerate your soil to loosen compaction. If your soil is suffering from compaction, the too-compact soil is cutting off circulation (air and water) to the root systems of your normal grass. Under these conditions, crabgrass and other forms of weeds thrive. Run an aerator over your lawn every season if you suspect it's too compact, especially if your soil contains high levels of clay.
  5. Overseed. Overseed your lawn to promote the right sort of growth. While you only have to overseed patches where crabgrass thrive, it might be helpful to overseed your entire lawn every two or three seasons.
  6. Clear out all dead crabgrass. Dead crabgrass can have an allelopathic effect, meaning it releases a toxin that stops other nearby plant growth. Completely remove any dead crabgrass plants from your lawn and dispose of them well away from your turf.[5]



Tips

  • If you have crabgrass, mow your lawn frequently to the maximum height recommended for your grass species. The frequent cutting will prevent the crabgrass from flowering and seeding, and your lawn grass will have an easier time crowding out all other weeds.
  • Corn gluten is a safe and effective natural alternative to synthetic pre-emergent herbicides.
  • Use synthetic herbicides sparingly, as they often contain chemicals that are harmful to people, pets, lawn critters you want to keep (like earthworms), and other parts of the ecosystem.
  • Check your local cooperative extension for tips specific to your area.
  • Remember, the best prevention is a full and thick lawn.
  • The best preventative measure for crabgrass is simply having a lush, healthy lawn. Maintain your lawn year-round to avoid a crabgrass invasion.
  • Once an herbicide container is opened, use the product as soon as possible. If left for too long, the product may lose its potency.

Warnings

  • Do not apply pre-emergent herbicides too late in the spring, they will do no good. Crabgrass generally emerges about the time of dogwood bloom, and pre-emergent herbicides do not affect crabgrass that is already up and growing.

Related Articles

Sources and Citations

  1. ↑ http://www.familyhandyman.com/landscaping/how-to-get-rid-of-crabgrass/view-all
  2. ↑ http://www.allaboutlawns.com/lawn-weeds-pests/10-steps-to-become-crabgrass-free.php
  3. ↑ http://turf.msu.edu/crabgrass-control-in-home-lawns
  4. ↑ http://www.dummies.com/how-to/content/how-much-fertilizer-to-apply-to-your-lawn.html
  5. ↑ https://www.acs.org/content/acs/en/pressroom/presspacs/2013/acs-presspac-june-26-2013/crabgrass-secret-the-despised-weed-makes-herbicide-to-kill-neighboring-plants.html

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