Crabgrass is one of the most commonly mis-identified lawn weeds. Lawn novices tend to call any thick-bladed grass, that is standing out in their otherwise fine bladed lawn, crabgrass. But sometimes the thicker bladed grass is just another lawn grass variety that was planted on a neighbor’s lawn or in the park around the corner. In the photo below we have a clump of tall fescue – not crabgrass.
Because it is thick bladed and much more heat and drought tolerant, it sticks out like a sore thumb in midsummer.
Here is what true crabgrass actually looks like. (You can also google "crabgrass" while in google images to see what it looks like in various stages.)
As you can see, it is not growing upright like most lawn grasses. It grows in a more prostrate fashion, close to the ground. The stems extend out like legs of a crab. It a lighter color (typically blue-green or yellow-green) than the desirable lawn grasses.
Crabgrass sprouts annually from seeds dropped the previous summer/fall. The seeds germinate when the soil has warmed up well – typically mid to late spring through early summer. The soil temperature needs to get to 55-60 degrees and stay there for about a week before crabgrass will sprout. In warmer climates it can sprout as early as February.
The crabgrass weakens the turf around it through root toxins and covers the grass in an unsightly circular patch (see below).
It produces numerous seeds and proceeds to drop them in the summer or early fall.
Crabgrass, which is an annual (grows for just one season) dies off soon after it has dropped its seeds, or as soon as it is hit by a frost. It shrivels up and pretty much disappears by the end of winter. You will not see any crabgrass on the lawn in early spring if the lawn was hit by frost. If you do see a clump of thick bladed grass in early spring, it is not crabgrass.
Preventing Crabgrass Naturally
Crabgrass can often be prevented by simply learning what it likes and dislikes, and then changing some things about your soil and how you take care of the lawn. I have seen numerous instances where crabgrass infestation stops at the property line of neighboring yards. I've also seen plenty of instances where lawns have been treated with chemical crabgrass preventer (pre-emergent) and crabgrass still sprouts, due to poor lawn or soil care.
Below are some things you can do to prevent crabgrass naturally.
Mow high. Crabgrass likes warm soil and sunlight. It doesn't grow in shady areas. Thick, taller lawns keep the soil cooler and prevent sunlight from reaching the soil. When you mow too short you allow the sun to reach the soil and warm it up faster than it should. You also weaken the lawn with short mowing, making it easier for crabgrass to take over.
Avoid scalping the edges of the lawn along walks and driveways or beds. Check the All About Mowing part 4 on our site to see how to mow edges properly Not only do people scalp lawns by incorrect mowing, but they also scalp the edges with weed wackers. Doing this is a sure way to promote Crabgrass. It shortens and weakens the grass and causes the soil to bake by the concrete.
Water ahead of Crabgrass season. If your lawn has plenty of moisture and is actively growing, it will be difficult for crabgrass to establish. Unfortunately, the typical homeowner won't water the lawn until it absolutely needs it - which is often late spring or early summer, about the same time crabgrass is ready to sprout. If the lawn is dried out, the blades are thinner and the grass may even be going into a dormant state or already. It is not going to compete or crowd out crabgrass very well in this state.
The typical homeowner eventually sees that the lawn is really dry and gives it a good soaking. But the grass will take a few days or more (some grasses will take weeks) to recuperate and begin growing again. In the meantime, the crabgrass seeds in the ground soak up the water and sprout before the grass has had time to thicken up.
Seed early and late. A thick lawn keeps out crabgrass. Thin or bare areas invite crabgrass in. Some grasses spread rapidly through either above or below-ground runners, and fill in bare spots. Other types won't spread much and simply need more plants to get the lawn thicker. In the spring you can get grass seed growing at least a few weeks before the soil is warm enough for Crabgrass to sprout. In the fall, after the crabgrass dies, there is usually plenty of time to seed all the thin areas of the lawn.
Improve Your Soil
Crabgrass loves compacted soil and clay. It also tolerates salt and other toxins and thrives in very dry as well as over-wet soil. Organic fertilizers, compost and other amendments can help change your soil structure. By treating the yard heavily with Aerify PLUS, you will help detoxify, aerate, relieve soil compaction and make crabgrass less likely to sprout.
Lime if needed. By improving your pH you will help get more nutrients to the grass, along with the Calcium that lime contains. More nutrients equals a healthier, more aggressive lawn. You can use a pelletized garden lime, or a Liquid Lime.
Also, make sure you water areas that tend to bake, like the curb section or wherever the grass dries out fast. In dry areas the desirable grass will weaken and thin out, making it easier for crabgrass to fill in.
Fertilize properly. As we said earlier, A thick lawn keeps out crabgrass. Good fertilizing will thicken the grass, making it harder for crabgrass to sprout. The key time to make sure fertilizer is available, when it comes to crabgrass, is after the initial spring flush of growth. You want to keep the grass growing aggressively before and during the time that crabgrass is trying to sprout. If you are using fast acting fertilizer, make sure to apply at this time.
If you are using a slow release, organic or natural lawn fertilizer, you can fertilize heavily in the spring and it can have a profound affect on crabgrass prevention. It will keep the lawn thick and green and spreading for a few months. For crabgrass prevention purposes we suggest applying whatever formulation you use in a way that ends up with up to 2 lbs of nitrogen per 1000 sf by mid-spring. This can be split into an early and mid-spring application, or just one very heavy early spring fertilizing. If it is a slow-release organic fertilizer, it will not burn.
Corn Gluten Meal is a popular natural fertilizer that also has substances in it that are purported to inhibit crabgrass and other weed seed germination. We have had fair to decent results using it. I'm I not sure how much those results are due to the weed inhibitor and how much are due to the heavy fertilizing it gives in one shot. The product is only effective when you apply at least 20 lbs per 1000 sf, which equates to approximately the same 2 lbs. of nitrogen that we mentioned above.
Summary
If you want to have a lawn that doesn't get crabgrass, you need to get aggressive. Ideally you would create a well-aerated soil and healthy soil that holds moisture due to good structure and humus. The roots of the grass would dig in deeply, and would be slow to dry out.
The lawn would be well-fertilized in the spring so it gets nice and thick. Any bare or thin spots would be seeded early. It would also have plenty of soil moisture to keep it actively growing when crabgrass season has begun.
The lawn would be tall, which helps shade the soil and also helps with deeper rooting. There would be no scalped edges inviting crabgrass to establish. If the grass is a shorter mowed type, it would be so thick that it still would have a dense canopy to shade and keep out crabgrass.
And finally, in the fall, any areas of lawn that are thin or bare would be seeded.
Stuart Franklin is president of Nature's Lawn & Garden, Inc. www.natureslawn.com
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