Lush Green Yard Care Blog

What Is Crabgrass?

crabgrass bunch growth

Crabgrass refers to a species of grasses that belong to the same grass family (Poaceae) as many desirable turfgrass types. However, unlike the grass that you would want in your lawn, crabgrass has many traits that make it an unwanted species. The unpleasant appearance and growth habits are what categorize crabgrass as a grassy weed rather than a desired turf, so it is important to know how to identify this intruder when it finds its way into your lawn.

The team here at Lush Green Services has assembled this guide to crabgrass to make sure that you know how to identify and prevent crabgrass in your Colorado lawn this summer. Be sure to check out our homeowner’s guide to lawn weeds for more information on weeds to look out for as you tend to your lawn!

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How To Identify Crabgrass

How to identify crabgrass

Before a crabgrass invasion grows and spreads throughout your yard, it may be difficult to detect it in the early stages of its development. One of the first things you should look for is the unattractive clump-type growth of crabgrass as it pops up in your lawn. Crabgrass disrupts the uniformity of your upright turfgrass because of this clumping growth, and also because of the outward, star-patterned growth of its leaves. When taking an overview of your lawn, these are the first things you will notice during a crabgrass invasion.

Upon closer inspection, crabgrass can also be identified by its slightly rolled stems that will typically appear white or faint pink at the base. It is often said that viewing crabgrass from above can reveal a crab leg-like appearance due to the weed’s long, sprawling stems, especially when a pink hue is present. Leaf blades of crabgrass, unlike most grass in lawns, could be slightly hairy and grow in opposite pairs up the stem, and they will be pointier than blades of most turfgrass. Crabgrass will also have a bright green color (or dark green, depending on the species), which differs from the color of grass in many lawns.

Lastly, crabgrass produces seed heads that are long and thin, kind of like fingers. They can be anywhere from 6 to 24 inches long, and they often have a reddish color at the tips. These seed heads appear in late summer or early fall, and they’re one of the ways that crabgrass spreads itself so quickly and easily.

Look For These In Your Lawn:

  • Leaves from faint yellow to dark green
  • Flat and wide leaves
  • Occasional hairs on the sheaths
  • Coarse texture on leaf blades
  • Long, rolled stems
  • Low, outward growth
  • Finger-like, spiky seed heads
  • Shallow, fibrous roots

Different Types Of Crabgass

The descriptions of crabgrass noted above are general characteristics of the plant, but there are several different types of crabgrass that can be found in lawns across the country. The most notable and prevalent species are small or smooth crabgrass (Digitaria ischaemum) and large or hairy crabgrass (Digitaria sanguinalis).

Smooth Crabgrass

crabgrass roots

Also known as small crabgrass, this species is the most common variety of crabgrass in the United States. As you can probably guess from the “small” nickname, this species develops smaller leaves and grows lower to the ground than large crabgrass. Typically, smooth/small crabgrass does not exceed 2-2.5 feet in length (in ideal conditions), and the individual blades of grass are slightly less wide than those of hairy crabgrass. This weed is also referred to as smooth crabgrass because the sheath and leaves of this species do not have any hairs, unlike its aforementioned counterpart. You may also be able to identify small crabgrass by a faintly red or pink stem that is observable when viewed from above.

Hairy Crabgrass

identifying hairy crabgrass

Hairy crabgrass is often referred to as large crabgrass, and both nicknames are clues on how to differentiate this species from smooth crabgrass. This variety is more common in the northern United States, while smooth crabgrass is more prevalent in the South. You will find both types of crabgrass here in Colorado, but our dry weather and soil conditions are more likely to breed hairy crabgrass. Its leaves tend to grow longer than those of small crabgrass, reaching maximum lengths of up to 3.5 feet. One of the quickest ways to identify hairy crabgrass is by finding small hairs growing on the sheaths of leaf blades, which are not present on smooth crabgrass. The leaves of large crabgrass are also typically wider than the leaves of small crabgrass, but height and hair are always your most obvious signs. Usually, but not always, hairy crabgrass stems will have a more white color near the base.

When & Where Does Crabgrass Grow?

crabgrass emerging
  • When: Crabgrass is a summer annual, meaning it thrives in warm temperatures and completes its life cycle in a single season. Seeds germinate when temperatures reach 55 degrees Fahrenheit. Throughout summer, crabgrass will ravage lawns until temperatures begin to cool down in fall. At that time, crabgrass will disperse seeds (in fall), and those seeds will overwinter in the soil until temperatures are warm again in spring, when crabgrass starts its life cycle over again.
  • Where: As a warm-season weed, crabgrass thrives in hot, dry conditions. It loves full sun and can tolerate (and even prefers) poor soil conditions. In fact, crabgrass is often one of the first weeds to appear in a lawn that is stressed by drought or other environmental factors. Crabgrass will also happily grow in areas of your lawn that are compacted or have poor drainage. Because crabgrass thrives in low-fertility soils, it often emerges before the grass in your lawn is able to survive, which will only make the soil even less fertile for your lawn.

How Does Crabgrass Spread?

crabgrass seedhead (2)

Once crabgrass takes hold in your lawn, it is difficult to get rid of. The plant can produce up to 150,000 seeds per season, which means that a single crabgrass plant can quickly turn into a full-blown infestation. Crabgrass also has shallow roots that make it difficult to pull out of the ground, and the plant often grows back quickly after being removed.

In addition, crabgrass seeds can remain dormant in the soil for several years before germinating. This means that even if you’re able to get rid of all the crabgrass plants in your lawn today, there’s a good chance that the weed will come back next year or even several years from now.

How To Prevent Crabgrass

The best way to prevent crabgrass is to have a healthy, thick lawn that crowds out the weed before it has a chance to take root. Once crabgrass emerges in your lawn and throughout your yard, it can be difficult to remove. Crabgrass is notorious for its shallow, fibrous roots that are very invasive and aggressive. The roots of your lawn will struggle to develop as crabgrass roots spread, so controlling the weed is crucial to your lawn’s success. Keep the following tips in mind for a lush lawn that is free from crabgrass this season, and call Lush Green Services today for even more help!

  • Pull Immature Crabgrass: Removing crabgrass before it develops a seed head is the best way to prevent an infestation in the following year.
  • Dig Out Roots: Established crabgrass will have roots that are slightly stronger, so digging down and around the fibrous roots is best.
  • Apply Pre-Emergent: Early spring is the best time to apply a pre-emergent weed killer, which prevents seedlings from being able to emerge.
  • Overseed In Fall & Spring: Keeping your lawn lush and thick is key to choking out crabgrass, and seeding is effective when crabgrass seeds are germinating.
  • Mow High: Prostrate growth and high sunlight requirements cause crabgrass to struggle in taller lawns, which also means deeper and healthier grass roots.
  • Use Grassy Weed Killers: If all else fails, small bunches of mature crabgrass can be removed by directly applying grassy weed killers, but professional help is always best due to the non-selective nature of these chemicals.
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