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Crabgrass next to a driveway in a drought stressed Bolingbrook lawn in mid August.

Crabgrass growing well next to a driveway in a drought stressed lawn in Bolingbrook, August 12th.

What is Crabgrass?

Crabgrass is a pesky annual grassy weed that originated from Europe. It can severely reduce the quality of your lawn in as quickly as a single season. That Weed Guy has years of experience with controlling crabgrass and we would love to help control it in your lawn. To get started, request a free estimate today!

When Does Crabgrass Germinate?

In the Chicago suburbs of northeastern Illinois, including Plainfield, Naperville, Bolingbrook, Crystal Lake, McHenry and all of the surrounding communities, crabgrass typically germinates from late April to early May. It can, however, fluctuate based on weather conditions (i.e., extreme drought, extra rainfall, early heat). We generally like to have the pre-emergent applied by the third week of April. However, we have seen cases, such as 2012, where weather was warm very early in the Spring, as well as in 2014 when winter hung on until the first week of April. This late winter also occurred in 2016. When winter hangs on, it delays the start of the crabgrass germination.

Are There Different Varieties of Crabgrass?

There are a couple of varieties of crabgrass that we are concerned with in our region, but the methods used to control both varieties for both are identical.

Crabgrass growing well in a drought stressed Bolingbrook lawn in mid August.

A closer photo of crabgrass in a drought stressed lawn in Bolingbrook, August 12th.

Large Crabgrass

Large crabgrass has the following characteristics:

  • Has 3-13 finger-like terminal spikes.
  • Does not have auricles.
  • Has ligules.
  • The first leaf of a seedling is short and wide with a blunt tip.
  • The leaves have a split sheath that has overlapping hairy margins.
  • Often killed by the first frost.
  • Each plant may produce up to 700 tillers.
  • Each plant can produce up to 150,000 seeds.
  • Seeds are elliptical to lance shaped.
  • White hairs at junction of leaf blade and sheath.

Small Crabgrass

Small crabgrass is similar to large crabgrass, but has the following characteristics:

  • Has 2-6 fingerlike terminal spikes.
  • The leaves are hairless.
  • There are a few long hairs at the junction of the blade and sheath.
  • Membranous ligule is 2-3mm long.
Mature crabgrass growing among spurge in a drought stricken Bolingbrook lawn in mid August.

A closeup photo of mature crabgrass growing among some spurge in a drought stricken lawn in Bolingbrook, August 12th.

How Can Crabgrass Be Controlled?

The most successful method of controlling crabgrass is to apply a pre-emergent to prevent it from germinating altogether. Once it has germinated and grown out of the seedling stage, it can be very difficult and expensive to control. One reason for the difficulty is that the weather usually turns hot and dry soon after it has germinated (late June/July). While post-emergent pesticides for crabgrass do exist, most of them can potentially damage the healthy grass if they are applied during these hot and dry conditions.

How Effective is the Crabgrass Pre-Emergent?

There are several factors that can have an impact on the effectiveness of the pre-emergent application. When all of these factors work out in your favor, which they almost never do, the pre-emergent treatment can last approximately 4-6 months (through July or September) depending on the material used. The pre-emergent works by forming a barrier on the surface of your lawn, which actually prevents all types of grass seed from germinating. The effectiveness of this barrier depends on the factors detailed below.

Selecting the Right Product

Applying a pre-emergent on mature crabgrass or applying a post-emergent prior to germination will have no effect on the crabgrass. It is important to select the right product, not only based on pre or post emergence, but also based on the types of grass that the products are designed for.

Timing of the Application

The timing of your pre-emergent treatment is critical. While there are a select few pre-emergent herbicides that can also kill seedlings, for the most part, you must apply the treatment before the crabgrass germinates.

Lawn Thickness and Thatch Levels

The thickness of your lawn and thatch levels can have both a positive and negative effect on your pre-emergent treatment. A thicker lawn will hold and shade the barrier longer, keeping it from running off and breaking down as quickly. If you have bare spots or other areas where there is little or no grass or vegetation, it is likely that you will still get crabgrass in these areas. While a thick lawn goes a long way towards preventing crabgrass and other weeds, too much thatch can actually cause the pre-emergent to degrade or runoff more quickly. This is yet another reason why we stress the importance of core aerating your lawn one to two times per year, which can help keep thatch levels in check over time.

Weather Conditions

Another factor is the amount of rainfall and heat your lawn receives during the 4 to 6 month period. If the rainfall or heat is heavier than average, it can breakdown the barrier more quickly.

Can I Seed My Lawn After Applying Crabgrass Pre-Emergent?

While we recommend doing all seeding in late summer / early fall (approximately between August 15th and September 15th), if you need to fill in some bare spots in the spring or summer, you still can. You will, however, need to rough up the soil to break the pre-emergent barrier. It is also recommended to apply fresh, black dirt over the top of the roughed up bare spot. If you need to overseed your entire lawn, it is best to wait until the period mentioned above. Besides the potential issues with the pre-emergent preventing your seed from germinating, your young seedlings will also have to deal with the heat and stress of summer, which is a big reason why so many spring or summer overseedings fail.

How Can That Weed Guy Help My Lawn?

If you feel that it is too much work to try to fix your crabgrass problems on your own, or you would like to leave it to the pros, That Weed Guy can help. Fill out the simple form on this page, give us a call, or request a free estimate today! We will personally visit your lawn and provide you with an in-depth analysis of any problems we might find, as well as a list of recommended solutions that we can help with.

Related Blog Entries

You Should Already Be Thinking About Crabgrass 2013 Feb 26


Gardner, David, Ph.D., “Crabgrass Control for 2012.” TURF. Feb. 2012: A14-A17. Print.

Royer, France, and Richard Dickenson. Weeds of the Northern U.S. and Canada. The University of Alberta Press and Lone Line Publishing, 2004. Print.

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