There’s a Small Window to Stop Crabgrass Before It Starts Growing – Here’s the Exact Moment to Act

Every weed does its best to survive, but some are craftier at this than others. If this were an Olympic sport, crabgrass might win the gold. This highly resilient summer annual does well in dry, compacted soil that other plants avoid, and it spreads quickly by tillers. Each plant produces up to 150,000 seeds that germinate the following spring. And the stems spread out low and wide like crab legs or spider legs, too low to hit with a lawn mower.

If you are ready to go to battle against crabgrass in your turfgrass, your best option is using a pre-emergent herbicide. You may have heard this type of crabgrass control called a crabgrass preventer. It can be very effective but only if you apply it in a very narrow window, before the crabgrass wakes up.

This “perfect moment” can be anywhere from February to May, depending on your climate. We’ll show you how to figure out the exact best moment in your own location.

Crabgrass Is Everywhere

Crabgrass is a common weed that grows in all 50 states, thriving in USDA Hardiness Zones 2 through 11. That means that your landscape is not exempt. If you aren’t familiar with crabgrass, its blades look like regular grass but wider. It grows in clumps, forming low, circular mats that look a bit like crab legs.

Where might you see crabgrass? It is often found in turfgrass lawns, particularly compacted or thin turf. Crabgrass loves hot, sunny conditions and grows quickly in full-sun locations.

You might also see it in cracks in your driveway. Crabgrass is not one of those weeds like dandelions, for example, that some people like to grow. It is considered a nuisance weed in every state.

Using Pre-emergent Herbicide on Crabgrass

The best way to get rid of crabgrass is to use pre-emergent lawn herbicides in the springtime. You have to be very careful to hit “the pre-emergent window” to apply the crabgrass preventer. The basic idea is to apply the herbicide before the grass seeds germinate. Some gardeners relate the timing to when the forsythia bushes are blooming. Their bright yellow flowers are among the earliest blossoms to open in spring. You can find Scotts Crabgrass & Grassy Weed Preventer on Amazon or from your local hardware store.

But it’s probably better to be more precise by basing your timing on the temperature of the soil. It’s more work but it’s worth it, since an application at the perfect time will not only prevent crabgrass from emerging but also other common weeds including chickweed.

When to Apply Crabgrass Preventer

This type of herbicide prevents the seeds from the last growing season from germinating. So you need to apply the pre-emergent herbicides before soil temperatures get warm enough for the seeds to germinate. That temperature, taken at 0-2 inches depth (0-5cm), is between 60 and 70 degrees F. Some 80 percent of seed germination takes place when temperatures are consistently between those temperatures.

So how to figure out the best moment? Use a soil thermometer to take readings starting on February 1 - if you live in the south, somewhat later if you live in the north. Keep checking every few days. Apply crabgrass preventer when the soil temperature reaches 55 degrees Fahrenheit for a few consecutive days.

A simple soil thermometer like this one from Urban Worm on Amazon has an easy-to-read color coded dial for fool-proof monitoring. Or you could opt for a 4-in-1 soil moisture meter, thermometer, pH meter, and light meter which is also available from Amazon.

Other Crabgrass Tips

• Mow your lawn a few days before you apply crabgrass preventer. This will help the preventer get down to the surface of the soil.
• Clear all leaves and other debris off of the lawn before you apply the herbicide.
• Avoid any type of soil disturbance, including seeding grass, around the time you are applying the crabgrass preventer.
• You’ll get the best crabgrass control if you split the application. Apply the first half in early spring, then the second half six to eight weeks later.
• Water in the product in the pre-emergent herbicides within 24 hours of application.
• Do everything you can to keep your turfgrass healthy and dense. This will involve adequate irrigation, fertilization, and mowing the grass high.

Crabgrass Prevention Essentials