The Best Ways To Kill Crabgrass Post-Emergent

By Brian Mounts | Dec 30, 2021

Chances are, even if you applied pre-emergent to your lawn in early spring, some crabgrass still managed to germinate. Don’t fret, though. There are post-emergent techniques available to help eradicate the pesky crabgrass that did sprout.

Applying selective herbicides

For large amounts of crabgrass in your lawn, the most efficient way to kill it is to mix a selective, post-emergent herbicide with a surfactant and spray the patches where crabgrass is rampant.

  • For Bermudagrass, Zoysia grass, and fescue, apply a selective post-emergent crabgrass killer containing quinclorac.
  • For buffalograss, Kentucky bluegrass, and perennial ryegrass, use a product containing mesotrione.
  • For St. Augustine grass and centipedegrass, use Celcius, an herbicide explicitly labeled for these two turfs.

Spot-treating with glyphosate

If you only have a little bit of crabgrass, spot-treating with glyphosate using a technique known as sponging may be the most effective method of getting rid of it. With sponging, the glyphosate travels down the crabgrass, killing the root.

  1. Let the crabgrass grow taller than the lawn by mowing around it for a couple of weeks.
  2. Carefully mix glyphosate in a bucket with a surfactant.
  3. Dip a sponge in the mixture and wipe the top two to three inches of the blades of grass.
  4. Repeat the sponging process every four to five days over two weeks to kill the entire weed.

Using baking soda to kill crabgrass

Baking soda acts as a desiccant due to its high sodium levels and damages almost any plant leaves it touches. The preferred method for killing weeds is to use the powder directly versus diluting it into a solution.

  1. Spray water on the crabgrass in your lawn.
  2. Sprinkle baking soda on the wet crabgrass blades until the weed is completely covered.
  3. Repeat after a few days, rewetting the weeds and sprinkling more sodium bicarbonate if needed.

Using vinegar as an herbicide

Vinegar is often used as an organic weed killer, especially when mixed with soap and salt. The soap breaks down the cuticle so the vinegar and salt can get inside the leaves. Once inside, they act as a desiccant by breaking down cell membranes, which pulls water out of the foliage to kill plants.

  1. Combine one gallon of 20% white vinegar, one cup of salt (table salt or Epsom salt), and one tablespoon of liquid dish soap in a bucket.
  2. Stir the solution with a plastic spatula or clean dowel to mix the ingredients well.
  3. Carefully pour this solution on the crabgrass, trying to keep it off of the turf blades.
  4. Continue to apply the vinegar solution every few days until the entire weed is killed.