Crabgrass illustration


Many homeowners call any grassy weed that they don’t like, or don’t recognize, as being crabgrass. Professional lawn care providers are often flooded with calls in early spring (northern climates) that crabgrass is growing and can they do anything about it. Of course, in early spring, crabgrass has not yet started to develop, but "crabgrass" is one weed name that most people can remember. Everyone knows what a dandelion looks like, but there's plenty of people that don't know what other weeds look like.

Crabgrass is a warm season annual grass which grows best in the heat of midsummer when desirable lawn grasses are often semi-dormant and offer little or no competition. Crabgrass overwinters as seed, comes up about mid-May or later, and is killed by the first hard frost in fall. Crabgrass grows prostrate and close to the ground, the stems extend out like the legs of a crab and it is usually lighter in color than the desirable lawn grasses. If you conclude that crabgrass was present last year, then it is likely that it will be a problem later on this year.

Crabgrass grows best in full sun. It does not grow in shady places. Crabgrass can be controlled in a number of ways, but the best defense against crabgrass is a thick vigorously growing lawn that is mowed no closer than 2 1/2" for cool season grasses.

Once the seed has germinated, pre-emergent controls will not be effective. Post-emergent controls are going to be the most effective if they are applied while the young plants are tender and just getting established. Time your applications to assure that most of the seeds have germinated or make more than one application.

Pre-emergent applications should be made when soil temperature are still below 50 for the best prevention of crabgrass. Pre-emergent applications are not recommended for areas where new grass seed is going to be planted during the first half of the growing season. Preemergent applications lose their effectiveness if the lawn is raked or disturbed during the first half of the growing season.

Once the crabgrass seed has germinated, pre-emergent applications are not effective. When this occurs a post emergence crabgrass herbicide is now available. These are products that are applied after the crabgrass seed has sprouted. The herbicide (ACCLAIM) gives excellent crabgrass control with one application. This product should be applied when crabgrass is in the 3 to 4 leaf stage of development. Once crabgrass has become established during the growing season, it is best to leave it alone and it will die back in the fall. Next season, apply a pre-emergent herbicide to control it. Over seed areas that were heavily infested with crabgrass in early fall to help fill in those areas.


Crabgrass and droughts

Ever notice when the weather heats up and drought conditions appear, that crabgrass seems to thrive? With the extreme heat and drought stress of summer and the loss of grass to things like billbug and brown patch, thin areas in many lawns are overtaken by crabgrass. Even without these pests, lawns next to sidewalks and driveways are particularly susceptible to crabgrass infestations. Lawns next to these hard surfaces are often times stressed because of the increased heat the surfaces create.

Sometimes even when preemergents have been properly applied, you may notice crabgrass growing along these hard surfaces if heavy rains fell in the spring after applying the control. The heavy rains are multiplied along the driveways and sidewalks, enough so to wash away the protective layer of the pre-emergent.

There are some products that can be used to kill crabgrass after it sprouts and becomes noticeable. Whether you opt for to spot treat for this depends on how big of an infestation you have. Large expanses of crabgrass are probably preferable to large expanses of dead grass going into the fall. Spotty crabgrass outbreaks are the most likely candidates for spot treatments.

Because crabgrass is an annual plant, it will die out with a killing frost. Make note of the infested areas and apply a pre-emergent herbicide in those areas next spring.

Organic crabgrass control

Crabgrass can easily be pulled by hand and this may be a great option for removing a few plants, especially if the plant can be removed before going "to seed". It is easier to pull the plants after a heavy rain.

Corn gluten can also be applied in early spring as an organic pre-emergent. This product suppresses crabgrass seed germination.

Other crabgrass control remedies

You don't have to look very hard to find off the wall crabgrass control home remedies on the internet. Many people think that just because a product can be found under the sink or the cabinet, that it is "safe" to use as a weed killer. This is far from true. Never use products, even if you already have them in your house. Using these products on the lawn can have unintended consequences and may be more dangerous than using products from the garden center that are labeled as crabgrass killer.