Most articles about crabgrass often start with a truly unhelpful "the best defense against crabgrass is a healthy lawn". While thats true, it's no what you want to hear in summer, when crabgrass is at full tilt and invading your lawn and the chance for prevention is long gone. So instead this article will try to help you identify it, kill it off, and only then turn to preventing it again next season.
First lets set some expectations. It's likely that if you have crabgrass in your lawn right now, it's been there for several years and has dropped thousands of seeds, which can take years to germinate. Crabgrass cannot be controlled in one growing season because of the great number of viable seeds that accumulate in the soil from years of infestation.
How to Identify Crabgrass
Crabgrass is an annual plant. It lives for one year, drops seeds, and then dies off in the early fall. It changes appearance extensively over the course of its short lifespan, and is relatively easy to take out early on, so identifying it quickly is important.
In its early stage, crabgrass will appear bright green, with thick silky and shiny leaves branching out from the center.
As it matures it will spread out, forming greenish-purple seed heads that will spread further, and crowd out other grasses which are not growing as quickly.
Mature crabgrass is the version that causes real problems in lawns. It will smother existing lawns in the process of releasing thousands of seeds which can lie in wait for several years before growing. And it happens quickly. Crabgrass is the fastest thing growing in your yard by July-August. It will can mature in the course of a few weeks in some situations.
It's important to point out that this battle will be fought over the course of several years. So prepare yourself for the long haul.
How to Kill Crabgrass:
Just pull it
In the early stage (the first 1-2 weeks after emerging) crabgrass can be pulled easily by hand, and is the preferred approach for small patches or individual plants.
Spray it
If you have a large infestation, you'll need to break out the spray. Post emergence herbicides can be used when crabgrass is in the 2- to 5-leaf stage. This is very early, when it has not yet put out a seed head, and still looks like a light green and thick grass blade.
Repeat applications may be required depending upon treatment specifics Make sure you're not using anything with chemicals that require full PPE to apply. We recommend this selective herbicide which uses Iron HEDTA product.
Solarize it
In late stage crabgrass (if it looks like the second picture) then you have to go nuclear. Wait until the sunniest and warmest period of the year, use your lawnmower to cut the lawn as short as you can, apply a generous amount of water, and use a sheet of clear plastic to cover the ground.
This process is called solarization, and it’s a good way to kill a large section of grass or weeds.
You need to ensure that the plastic isn’t punctured in any way. Leave it on the ground for between a month and six weeks. During this time you’ll answer the same question repeatedly when all your neighbors ask what the heck you’re doing, and the sheet and the ground beneath will heat the ground sufficiently to destroy all the seeds below it.
After this, you can reseed the area with grass seed, or put down sod
Boil it
Finally, you can use boiling water on mature crabgrass. This method is especially effective because it will instantly kill any seeds that come in contact with the boiling water. Just watch out for your lawn!
Bonus tip: Keep Mowing!
It’s ok to mulch clippings as long as you are mowing often. Frequent mowing prevents the plant from reaching maturity and developing a seed head. However, if you see a seed head that looks like this (see below), start bagging the clippings and dispose of them far away from your lawn.
How to prevent crabgrass from returning next season
The focus here is on preventing the crabgrass seeds from germinating in the spring, and over the course of the next few seasons.
- Seed in late summer or early fall. This is when your lawn is growing quickly and can support new growth, and Crabgrass and other annual grasses that germinate in late summer will begin to die off.
- Mow your lawn at a 3- to 4-inch height of cut. The taller grass shades the soil and keeps soil cool. Crabgrass seeds do not germinate under cool conditions. Adjust your cutting height depending on the turfgrass species. Rye and bluegrass can be cut on the low side, and Fescue likes to be cut taller, near 4 inches.
- Water deeply once or twice a week and avoid frequent light irrigation. Crabgrass has a very shallow root system, and will thrive in lawns that get short, frequent bursts of water, where the water stays close to the surface.
- Avoid summer fertilization. Crabgrass benefits more from fertilizer application under high temperatures than Rye, Fescue, or Kentucky bluegrass. In fact, you will add stress and increase the risk of disease by adding a high dose of nitrogen rich fertilizer to your cool season lawn in the summer.
- Use a pre-emergent next spring to prevent the existing seeds from germinating when soil temperatures reach optimal range for crabgrass germination. Lawnbright plans offer an organic, corn based pre-emergent which ships when the timing is perfect for crabgrass to germinate in your area, taking all of the guesswork out of the equation.
Crabgrass is one of the fiercest lawn adversaries, but with enough patience and the right guidance, the battle can be won. Just be prepared for a long war.