Some tolerate crabgrass, while others actively try to control it. Yet, I’ve never met anyone who likes it. While considered a pest in lawns and landscapes, crabgrass is high in protein and easily digested by livestock. It is drought-tolerant and is considered a famine crop.
The seeds can be harvested and ground into flour or cooked whole, similar to couscous. In other parts of the world, it is a staple grain. But let’s be honest, you’re not reading this to learn about the uses of crabgrass. You want to know how to kill it. We will get to that, but first, we need to lay a foundation that will help with control.
What’s crabgrass?
There are two common species that thrive in our low-cut lawns, smooth crabgrass and large/hairy crabgrass. We’ll refer to both as crabgrass for this article, as management is identical.
Crabgrass is a summer annual grass. It germinates in the spring, grows over summer, flowers and sets seed in late summer, and dies completely in the fall, leaving only its seed to continue the cycle next year.
How did it get in my yard?
Studies show that crabgrass seed can survive up to three years buried in the soil. Considering some plant seeds survive for decades or longer, three years isn’t that long, relatively. However, crabgrass is a colonizing species. It can thrive in disturbed soils.
For example, if you just installed a new fence or patio, it wouldn’t be a big surprise if crabgrass shows up next year where you were digging if the soil remained mostly bare. Crabgrass seed can also blow in or be brought into your yard by foraging wildlife.
Controlling crabgrass
If you have had crabgrass problems in the past, the simplest way to prevent it from returning next spring is a preemergent herbicide, also called a crabgrass preventer. Active ingredients vary, but most crabgrass preventers include fertilizer as a convenience to the homeowner.
It is recommended to avoid these products, as they compromise the ideal timing for either herbicide or fertilizer applications. Finding a crabgrass preemergent without fertilizer may require talking with your local garden center or ordering it online.
Timing is critical for preemergent application, as it prevents the weed seed from successfully germinating. Apply too late, and the crabgrass preventer won’t work. Crabgrass germinates when soil temperatures reach 55 degrees Fahrenheit for a few consecutive days.
However, you want your preemergent down before germination. The yellow spring flowers of forsythia are often used as an indicator that it is time to apply crabgrass preventer. Forsythia works in most cases, but not all, so don’t put all your faith in its bloom.
If crabgrass has already sprouted, post-emergent herbicides containing quinclorac can be used to kill young plants through June. Late-season herbicides are often a waste, as the plants have already gone to seed and are about to die naturally.
The best defense
Whether you use herbicides or not, the best way to combat crabgrass is to have a dense, tall stand of lawn. Crabgrass thrives in a low-cut lawn. Raise the mower deck to three inches or higher to make your lawn more competitive against crabgrass. In addition, regularly overseed and apply fertilizer in the late summer to early fall for cool-season lawns.
If it is growing in your yard, don’t sweat it. Crabgrass dies every year and can be controlled given enough time. Plus, there are far worse weeds to deal with when it comes to our lawns. I’m looking at you, quackgrass.
