Crab Grass

Crab Grass/Crabgrass (Digitaria ssp.)

This summer annual is also known as Summer Grass.

Photo: Marek Uliasz

With so many different genus of grass weeds having similar features, we often have difficulty noting these differences.  Because of this, grassy weeds are often referred to as crab or summer grass.  They are not the same.

Depending on they species and location, Digitaria can be both cool season and warm season annuals. All are very similar in many ways with minor differences in the flower stalk structures.

The emerging weed starts as a sprouting single stem in spring. It then divides at the base into two, then multiple branch stems. It grows flat along the ground then grows upward into a round branching cluster. As growing season progresses, the maturing leaves turn a darker red.

Tall, thin stems have spike-like branches at the top where seeds are located, also called the panicle. These branches have a digit, or finger-like, appearance, which is where this species gets it's name - Digitaria. Digitus is Latin for 'finger' (and 'toe').

There are about 300 types in Digitaria ssp. worldwide. The two that are more likely to be seen in North America are:

  • Smooth (D. ischaemum) - This is a low growing up to about 6 inches and what we gardeners and lawn fanatics dislike. Leaves are smooth and at the young stage can blend into the lawn easily, even though they are a lighter green in color and have a point at the top. This spreads by seeds and rooted nodes.

  • Hairy, or Large Crab Grass (D. sanguinalis) - This is more likely to be found in orchards, vineyards, grasslands and various agricultural settings. It can grow up to 2 feet tall and spreads by seeds and rooted nodes. Leaves are also light green but rather than being smooth, they are hairy. Because the digits are especially pronounced with this species, there is yet another name given to it - Finger Grass.

The root system of crabgrass is shallow and grows in thin turf with poor soil qualities. Seeds can spread by grass cutting, wind, water and other methods. It can withstand dry soil, areas that are watered lightly and poorly drained soils. Water your garden well but make sure water doesn't stand.

Seeds germinate about the same time white dandelion puff balls form. Seed heads form late summer to early fall up until the first frosts.

Weeds can be pulled easily at the beginning of spring. They are usually clumped helping them to come out. Overall because of the shallow root system crab grass can easy to remove. As more cluster patches form, other vegetation is likely to be smothered out if not removed.

Replant bare, open spots immediately with flowers or place mulch in garden. If there are times where removal can be difficult to pull, try to hoe and mulch.

If larger area are effected try an inorganic mulch like solarizing black plastic mulch for a few weeks and apply an organic mulch type. In the spring consider a pre -emergent.

The best time to apply a pre-emergent herbicide is in spring only when certain there will be no more frosts, and temperature is above 53 degrees consistently. Do this before summer weather gets hot.

Be cautioned that it's probably best to apply a preemergent to lawn areas only where soil is exposed. If applying a preemergent in lawns remember other 'good' seeds are also likely to be killed.

Other FYI's about crab grass

  • Crab Grass is one of the few weeds that spreads by seed and rooted nodes only - not by rhizomes and stolons. Most weeds have the ability to spread by seeds, rhizomes and stolons.

  • Not only is wheat (Triticum ssp.) important to us providing food sources such as cereal, maize and forage for cattle, but some Digitaria grass weeds are too. Millet of digitaria species is called fonio and benefits people around the world creating cereals, porridge, it can be toasted, fermented for beer and can also be forage for cattle.

Related Articles:

          Growing Plants from Seed
                  More suggestions for removing weed seeds.

Back to Weed Identification

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