Posted on

crabgrass weeds with seed

Weed of the Month: Crabgrass

It’s late summer and crabgrass weeds have invaded some lawns. Unfortunately, crabgrass is very difficult to control with most herbicides once it develops a few tillers or branches. There are several species of crabgrass (Digitaria spp.): tropical crabgrass, smooth crabgrass, India crabgrass, large crabgrass, Southern crabgrass, and blanket crabgrass. All of them are summer annuals that germinate primarily in spring, grow during the summer, set seeds, and then die with the first frost.

Closeup of crabgrass (Digitaria spp.) going to seed in a thin lawn.
Jackie Jordan, ©2019, Horticulture Extension Agent, Clemson Extension.

Crabgrass is native to Europe and Eurasia and is a problem worldwide. The plant was originally introduced into the United States as a potential forage crop in 1849. Crabgrass is tolerant of heat and drought and is quick growing. A single plant can produce 150,000 seeds. The prolific nature of crabgrass makes control efforts a yearly task. Controlling crabgrass in a home lawn requires sound cultural practices and using pre-emergent herbicides at the correct time.

Crabgrass seeds require lots of light to germinate. A thick stand of turf is the best defense for limiting crabgrass weeds. Make sure that the lawn is being cut at the correct height for your turfgrass species. Scalping the lawn will expose the soil and reduces the vigor of the grass. Keep your lawn mower blades sharp, which ensures the turfgrass recovers quickly from mowing. To find information on the correct mowing height for your lawn, please see HGIC 1205, Mowing Lawns.

Proper irrigation is also important for limiting weed infestations. During heat or drought conditions, lawns should receive deep but infrequent irrigations. Watering everyday or every other day provides plenty of soil surface moisture for weed seed germination, including for crabgrass. Find more information on properly watering lawns, please see HGIC 1207, Watering Lawns.

Preemergent herbicides are best applied in early/mid-February and repeated in 8 to 10 weeks for adequate control. Crabgrass seeds start germinating once there are five consecutive days of 70 °F during early spring, but additional seed may germinate as late as June. All granular pre-emergent herbicides must be watered in with ½ inch of irrigation to make sure the product dissolves and the herbicide reaches the correct depth to provide effective control. Adequately irrigate the lawn within seven days of application or else the product is degraded by sunlight. For a list of products to control crabgrass and other grassy weeds, please see HGIC 2300, Grassy Weeds.

If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.

Author(s)

Jackie Jordan, Commercial Horticulture Agent, Fairfield, Kershaw, and Richland County, Clemson Extension, Clemson University

Crabgrass weeds with seed

An Opportunistic Annual Grass that Grows in Bare Spots with Sunlight

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur posuere, velit at auctor convallis, lacus erat commodo nisl, eget gravida nulla magna eget magna.

What Is Crabgrass?

Crabgrass is an opportunistic annual grass that sprouts in the late Spring, anywhere there is bare soil, water, and sunlight. Crabgrass continues to grow all Summer and doesn’t really become ugly until late Summer when it spreads seeds. After this time, Crabgrass is killed by the cold Winter, but the seeds remain intact for the next year. If you are on our Organic Foundation Lawn Care Program , you are gradually building your lawns resistance to Crabgrass. The longer you use our fertilizers, the better able your lawn will be to resist weeds.

As a side note, Crabgrass is not actually bad for your lawn. It won’t crowd out your desired grasses, even though it looks like it does. The only problem with Crabgrass is that it looks bad at the end of Summer. If it doesn’t bother you, it isn’t doing any harm to your lawn.

Why Do You Have Crabgrass?

BARE SPOTS
Crabgrass is opportunistic. It will prosper in any areas that have bare soil and receive sunlight. This often occurs around the edges of the driveway, sidewalk and tree lawn. Our suggested solution is to seed any damaged areas in the Fall and again in the early Spring to try to prevent bare areas and prevent Crabgrass from germinating.

SALTY SOIL ALONG YOUR TREE LAWN
Crabgrass loves salt. If you live in an area with salted roads, your tree lawn is at a high risk for Crabgrass. One recommendation would be to sign up for our Liquid Aeration service in the Spring and Fall, which will help reduce the amount of salt in the soil. Seeding bare areas in the Spring and Fall will also help.

MOWING TOO SHORT
University Studies show that mowing your grass tall, approximately 3.5-4 inches in height, will prevent more Crabgrass than any chemical on the market. The tall grass shades the soil surface and helps prevent Crabgrass from receiving the light it needs to grow. So start mowing high in April and continue to do so until October, when you can start lowering your cutting height before Winter. If you really like the look of a nice short lawn, you might consider seeding with our Green Microclover , which will shade the soil and prevent weeds, even if its mowed short.

WATERING TOO FREQUENTLY
Your soil is full of Crabgrass seeds just waiting to germinate. Daily watering helps Crabgrass seeds sprout. For the best defense against Crabgrass, don’t water more than 2 times per week, applying enough water to fill up a tuna can in each session.

GOOD WEATHER CONDITIONS FOR CRABGRASS
Some years have perfect weather for Crabgrass. An especially rainy Spring will help Crabgrass germinate, and a hot Summer will help it grow, while other grasses go dormant. While you can’t fight Mother Nature, you can maintain a thick lawn and mow it high!

What Can You Do If You Have Crabgrass?

Unfortunately, there isn’t much you can do about Crabgrass, once you get it. The best solution is to thicken your lawn later in the Summer by seeding to help prevent Crabgrass from returning the next year. Below are a few other suggestions.

HAND PULLING
If it is manageable, one option is to pull Crabgrass out by hand, or with a weed pulling tool, such as the Weed Out, which is perfect for remove this Crabgrass. If your lawn has a lot of Crabgrass, you may need to live with it this year, but work toward preventing it next year.

SPOT CHEMICAL SPRAY
There are chemicals that sometimes work to kill Crabgrass. However, they’re not completely effective. If the Crabgrass is already big and ugly, the chemicals will just turn it purple and more unattractive. Your best bet is to let Mother Nature take her course and kill it with cold weather.

THICKEN YOUR LAWN & MINIMIZE BARE PATCHES
A thick, healthy lawn is the best defense against Crabgrass. Seeding in the late Summer will add tougher, modern grasses that compete well with Crabgrass. Slice Seeding is great if the problem is throughout your lawn. If it’s just patches, rough up the dirt and seed in the Fall and/or Spring.

USE GOOD NATURE FERTILIZERS
The fertilizers in our Organic Foundation Lawn Care Program help to increase your lawns resistance to issues, such as Crabgrass. Our program works to continuously strengthen your lawn over time, so the longer you use our fertilizers, the more weed-resistant your lawn will become.

MOWING HEIGHT
Don’t forget to mow high starting next Spring, to help keep weed seeds from sprouting!

WATER PROPERLY
Remember to water your lawn next Spring and Summer in 2 sessions per week, to reduce germination. Avoid watering for short periods of time every day, which promotes the germination of Crabgrass and other weeds.

What Can I Do About Crabgrass?

The arrival of springtime means budding flowers, blossoming trees, and green grass. Unfortunately, with this abundance of new growth comes sprouting weeds as well. Crabgrass in particular is a weed that continues to frustrate homeowners year after year. By knowing how a weed grows and a few tips on natural prevention, you’ll know what you can do about crabgrass without chemicals.

What Is Crabgrass?

Crabgrass is an annual weed whose seeds germinate during spring and summer. Crabgrass germination occurs when soil temps reach 55°- 65°F at a 3″ depth for 5 consecutive days. Un-germinated seeds can wait in the soil for up to thirty years before sprouting. Given the fact a single crabgrass plant can produce 150,000 seeds during the growing season, it’s easy to see why controlling it is difficult.

Why Do I Have So Much Crabgrass?

Crabgrass favors sandy, compacted soil where the grass is in a weakened, thinned condition. Bare, thin lawns allow sunlight to directly hit the soil, which is an ideal condition for crabgrass germination. In addition, weeds like crabgrass thrive when your lawn has excess water and phosphorus levels.

How Can I Prevent Crabgrass?

The key to crabgrass prevention is to stack the playing field in favor of your grass; in other words, give it ideal growing conditions, and your grass will choke out weeds. Of course, you can make all the conditions favorable for turf-grass, but you also need to ensure you have the correct turf grass for your area. For example, bluegrass is a cool-season grass best suited for the northern US and won’t thrive in southern states.

Providing ideal growing conditions for your grass is very important and most are simple cultural changes. First, adjust your mower’s height to allow your grass to grow to its optimal level. The higher your grass is above ground, the longer the roots are underground; this means less room for anything else to take root. Aeration and overseeding can also decrease the presence of crabgrass, because it adds grass seed and favorable grass conditions to your lawn. Lastly, ensure your lawn’s soil has the proper amounts of nutrients via a simple soil test. Soil testing will help you determine what compounds and nutrients your lawn is lacking so you can fortify your lawn with a natural fertilizer, which will correct any inequities.

How Can I Kill Crabgrass?

Don’t give up if you’ve tried all the cultural practices and natural crabgrass controls we recommended above. If crabgrass is still kicking your butt — you still have options. First, you can apply a pre-emergent fertilizer before the germination period to organically control crabgrass. If it is mid-summer and the crabgrass is already fully grown, you can wait it out and then attack in full force next season or treat it with an herbicide specifically labeled for crabgrass control. Spraying herbicidal weed control is always a last-ditch effort and should be done so with care. When using any type of control materials always follow label directions, and only spray the troublesome areas as opposed to treating your entire lawn.

If you would like assistance with removing crabgrass from your yard, contact a local natural lawn care professional. NaturaLawn of America has provided homeowners with safer and effective, organic-based lawn care since 1987.