Weeds: Crabgrass

This is the third in a series of blogs, shared with permission, about weeds in the garden. Each blog will discuss a common and specific weed found in Maine, its history, uses, what story it tells about the soil it grows in, and how to get rid of it. The original blogs, along with other gardening related blogs, can be found here.

Crabgrass is actually a short form for a number of types of the same species of plant. In this article I talk about large crabgrass or Digitaria sanguinalius which is a remarkable plant with the ability to smother other weeds and act as its own mulch. A variety of other common names for it exist, including Polish Millet, hairy crabgrass, hairy finger-grass, crab finger grass, and purple crabgrass. About 10% of people are allergic to it, but if you aren’t among that 10%, rethink your hate of crabgrass.

Crabgrass, like many weeds I’ve been learning about, was brought to the United States. The grass is highly nutritious and is used by farmers for graze for animals. The seed is edible, and the plant is considered to produce a high amount of grain. Each plant can produce about 150,000 seeds each! The seed can be used as a flour, grain or fermented for use in beer. It is also very fast growing – producing edible seeds in just eight weeks. Eastern Europeans used it as a grain, called kasha, and cultivated it in sandy soils in Poland. We basically decided that corn sold better, and thus stopped cultivating it here in the U.S!

What does it mean?

Crabgrass indicates very low levels of calcium and phosphorus, low pH, low humus, very high chlorine levels and high levels of magnesium and potassium.  Basically,  you have poor soil. You will need to really work to fix the soil health to fully eliminate it, but it is a grain – so if you don’t also stop future spread, it could simply become healthier as you improve the soil.

It is difficult to kill because it prefers bad soil and drought. Also, it easily regenerates and is fairly tolerant to chemicals. The best way to get rid of it is to keep your lawn at least 2-3 inches tall and properly moist. Fertilize regularly and choose grasses suitable for your climate. You could also apply corn gluten meal to your lawn 2-3 weeks before the seeds begin to germinate, but this can inhibit all grass seed germination. One last option: remove large sections of turf around the crab grass and kill off any remaining weed seeds in that area before reseeding.

Want to learn more?

If you would like to learn more about weeds, why they grow, and what that means about your garden, consider the following texts:

Weeds and Why they Grow, by Jay L. McCaman

Weeds and What They Tell Us, by Ehrenfried E. Pfeiffer