Crabgrass is a common, invasive weed that can become a significant nuisance in lawns and gardens. It thrives in warm, sunny environments and is characterized by its fast-growing, low-lying stems and wide, coarse leaves. This aggressive weed can spread rapidly and quickly out-compete desirable plants and grasses, leading to unsightly landscapes.
What does crabgrass look like?
Crabgrass is a tenacious annual weed that thrives in hot weather. There are two closely related species: large or hairy crabgrass (Digitaria sanguinalis) and small or smooth crabgrass (Digitaria ischaemum).
The coarse-textured, light green to yellowish-green leaves are wider than traditional turfgrass blades. Its round stems are often reddish-purple and can be smooth or slightly hairy, depending on the type.
You often see crabgrass growing in low-to-the-ground clumps instead of spreading across your lawn. Its low, spreading growth habit forms dense mats that can smother other plants. As it grows, crabgrass puts out branches, or tillers, that look like crab legs, hence its name. The stems often lay flat and can root at the nodes, further anchoring the plant and allowing it to spread.
Crabgrass produces distinctive seed heads that resemble fingers extending from a central point, giving it a hand-like appearance. These seed heads usually have 2-9 slender spikes and can appear green or purple.
A fibrous root system helps it anchor firmly into the soil and absorb nutrients efficiently.
Crabgrass life cycle
As a summer annual weed, crabgrass completes its life cycle in a single season: it germinates in spring, matures during the warm season, and dies at the first frost.
Seed germination is directly related to soil temperature. When the surface soil temp reaches 55 to 60 degrees Fahrenheit and stays there for a handful of consecutive days, crabgrass seeds begin germinating.
Crabgrass seeds germinate best from early spring through late summer. Seeds typically stop germinating when soil temperatures reach 95 degrees Fahrenheit; the heat signals to the seeds that conditions aren’t conducive for them to sprout and finish their life cycle before the end of the season.
After germination, crabgrass grows through summer heat and starts to slow as the days become shorter. The shorter days trigger plants to enter their reproductive stage, passing their genetic information to another generation.
Purplish seed heads form on the plants until the first frost hits, with each plant producing around 150,000 seeds. These seeds will lie dormant through the winter until soil temperatures warm up again in spring. Then, the process begins again.
Conditions that favor crabgrass
If you’re struggling with crabgrass, don’t worry. You’re not alone! Crabgrass is opportunistic. You can find it in almost every turf and landscape situation. It’s prolific in lawns, gardens, athletic fields, golf courses, orchards, pastures, and ditch banks.
Crabgrass especially loves the following conditions:
- Hot temperatures
- Dry weather
- Light, frequent irrigation
- Sandy soils
- Thin turf or turf with areas of bare soil
- Scalped grass
- Compacted soil
- Thin soil
- Poor quality soil
- Stressed lawns
How to prevent crabgrass
Growing a thick, healthy lawn is one of the best ways to keep crabgrass out of your yard and garden. Maintaining the correct mowing height, proper fertilization using conventional or organic products, watering for the correct time, and overseeding thin or bare spots form a solid foundation for weed control.
For more information on management, check out our article on getting rid of crabgrass where we cover eradication and prevention methods.
FAQs about crabgrass
What is the difference between crabgrass and quackgrass?
Both weeds have wide, grasslike blades, but that’s the end of their similarities. Crabgrass is a light green or greenish yellow warm-season annual weed that grows horizontally and has a shallow, fibrous root system. Quackgrass is a bluish-green cool-season perennial weed that grows upright and spreads via underground rhizomes.
Does mowing crabgrass spread it?
If your crabgrass is young and doesn’t have seed heads yet, mowing won’t spread it across your lawn. However, if it is mature and has developed seeds, you will spread it if you mow and don’t bag the grass clippings.
Will a broadleaf herbicide kill crabgrass?
No, a broadleaf herbicide will not kill crabgrass. Broadleaf herbicides are selective and target broadleaf weeds like dandelions, clover, and pigweed. You need to use a non-selective herbicide like glyphosate or a selective herbicide formulated for grassy weeds to kill crabgrass.
Keep crabgrass from getting out of control
Crabgrass is an aggressive weed that can quickly become a significant headache in lawns. The best weed control method is keeping your grass healthy, which prevents crabgrass from becoming a huge problem.
Fertilizing, irrigating, and mowing all take time, though. If these tasks are too much for your to-do list and crabgrass has gotten out of control, contact a local professional to conquer your crabgrass and restore your lawn.
Main Photo Credit: Rasbak | Wikimedia Commons | CC BY-SA 3.0
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