What is crabgrass? How to get rid of the persistent weed

• Crabgrass grows in bare spots on your lawn, and it's in constant competition with grass.
• Use an herbicide to remove patches of crabgrass before they flower or remove clumps by hand.
• To prevent future growth, sprinkle grass seed on the treated spots immediately after weeding.

If creeping patches of crabgrass on your otherwise lush lawn are making you crabby, there are some simple steps you can take to remove the common weed.

You can remove small spots of crabgrass by using an herbicide, or you can pull patches of weeds by hand. However, there are certain times that you should take another route entirely, says Frank S. Rossi, Ph.D., New York State turfgrass extension specialist and associate professor of horticulture at Cornell University's School of Integrative Plant Science.

Read on to learn how to treat problem spots of crabgrass, how to recognize when the crabgrass has won over your lawn, and what steps you can take now to promote a beautiful, weed-free lawn next spring.

What is crabgrass?

Crabgrass (Digitaria) is an annual grassy weed that grows in low-to-the-ground clumps in bare spots on your lawn. As crabgrass grows, its green grass-like leaves spread out from the center of the plant. The resulting pattern resembles a crustacean - lending the weed its fitting common name.

Crabgrass thrives under a couple of key seasonal conditions: heat and dry weather. These same two factors hamper the growth of the more desirable healthy lawn grasses which crabgrass often smothers and competes for space with.

The prevalence of heat and dry weather in the summertime, and the hardy nature and life cycle of crabgrass compared to lawn grass, help to explain why crabgrass is so pervasive in many US regions in the summertime. By the time you notice crabgrass emerging, it may be too late to save your lawn - at least this year.

"If your lawn is more than 50% crabgrass, it's time to replant," says Rossi. If this is your situation, you can help your lawn grasses win the "survival of the fittest" battle next year by taking some simple preventative steps right now.

If your goal is to remove a few emergent problem weeds, Rossi says spot treatment will work - as long as you time it correctly.

When to kill crabgrass

Before you learn how to kill crabgrass, you need to know when to kill crabgrass. It's important to do it at a certain point in the plant's life cycle.

Crabgrass reproduces from seed which germinates under specific conditions.

"In most climates in the continental US, crabgrass is a summer annual, which means that when the soil is 50 - 60 degrees Fahrenheit for five to seven days in a row, you will have the perfect time for it to germinate to seed," explains Rossi.

Once crabgrass germinates, it grows rapidly. It is in constant competition with lawn grasses, which typically experience their first significant growth of the season well after crabgrass weeds begin to develop. By the time a crabgrass weed dies in fall, it will have produced as many as 150,000 seeds, which are left behind in the soil to germinate the next spring.

Weeding strategically in order to interrupt the plant's life cycle is important, says Rossi. "If you have only a few plants, pull them out before they go to flower. You don't want to add to the seed bank," he says. When crabgrass flowers, you'll see tall, spindly offshoots with purple tips.

How to remove crabgrass by hand

1. Prepare the soil: The best time to pull crabgrass is after a good rain, when the soil is loose.
2. Pull up crabgrass: Put on gardening gloves. Using a garden weeding tool, pull up the weed clump. Be sure to get all the roots.
3. Sprinkle grass seed on the weeded area (for lawns) or spread mulch (in flower beds). Do this immediately so that crabgrass doesn't re-root.

How to get rid of crabgrass with an herbicide

1. Choose a selective herbicide formulated for crabgrass. Selective herbicides are formulated to only kill what you want it to kill. Non-selective herbicides kill everything - including healthy grass. "We generally don't recommend those," says Rossi.
2. Spray product on the weed, following product directions.
3. Once the weed dies, rake it and remove debris. This could take anywhere from a couple of hours to a couple of days.
4. Cover the bare spot with grass seed or mulch. By planting new lawn grass seed, you eliminate the opportunity for new crabgrass seeds to root.

Quick tip: To get help with lawn problems and for information on recommended products and timing for your region, reach out to your county extension office. "Your local extension office is a best-kept secret," says Rossi.

How to prevent crabgrass from growing back

The key to preventing crabgrass after removing problem spots is maintaining a dense, healthy lawn, says Rossi. "If you have a lawn and you don't plant some seed, you are likely to get crabgrass," warns Rossi. He says you can discourage future crabgrass growth by taking the following steps now

• Plant high-quality grass seed between mid-August and mid-October to prevent spring and summer weed growth.
• Apply a nitrogen fertilizer once you have your lawn planted to encourage dense, healthy lawn grasses.
• Cover flower beds and vegetable gardens in black landscaping plastic and lay down mulch in flower beds to prevent weed growth.

Insider's takeaway

You can remove patches of crabgrass by applying a selective crabgrass herbicide, or you can hand pull spots of weeds.

In order to plan the most effective treatment, it's important to know where a crabgrass plant is in its annual life cycle. When treating weed spots, apply herbicide or pull them before the plant flowers.

A healthy, dense lawn is the key to effective crabgrass prevention. Plant high-quality grass seed from mid-August to mid-October for best results next spring.