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Crab Grass has taken over my lawn this year, it was bad last year, but it's even worse this year. What can I do? Missy


Crab Grass Hi Missy,
In this region, most grasses fall into two broad categories: cool season grasses (e.g., rye grass, fescues, bluegrass) and warm season grasses (e.g., crabgrass, Bermuda grass, Zoysia grass). Cool-season grasses thrive in temperatures from 65 to 75° F. When the temperatures are right, the cool-season species emerge from dormancy and grow very rapidly in the spring. They are generally intolerant of summer stress periods, and growth is slowed in midsummer; some go into dormancy and actually turn brown (they are not dead, just dormant). Their growth increases in the fall, but not to the same extent as the growth rate of spring. Warm-season grasses are best adapted to temperatures between 80 and 95° F. Warm-season species emerge from dormancy more slowly in the spring and grow strongly when temperatures are hot. They go into dormancy in the fall when soil temperatures drop below 50°.

Crabgrass is an annual warm-season grass that favors poor soil conditions, i.e., soil low in calcium; compacted; acidic; in sunny areas; over septic tanks, along walks and driveways where the radiant heat helps warm the soil.

A review of the temperatures this year; tells us why crabgrass is so bad. Since April 1, there have been 5 weeks that were too cold for either cool or warm season grasses; since June 1, there have been 3 weeks that supported cool season grasses, but 7 weeks that supported warm season grasses. Basically, it stayed cooler longer and warmed up quickly this year, so the warm season crabgrass has been able to out-compete the cool season grasses through the first week of August. The cool season grasses never got a good start.

While we can't control Mother Nature, there are several things that can be done that will help control crabgrass. A single crabgrass plant is capable of producing 150,000 seeds. Hence, it's difficult to eradicate crab grass since the seeds can lay dormant in the soil for 15-20 years and over time, work to the surface. Controlling seed production for several years will help reduce the viable seed supply. The single most important thing you can do is to never mow your lawn shorter than 3-1/2 inches (longer would be better) because crabgrass does not like the shade provided by longer grass. Secondly, get your soil tested and correct the pH if the soil is too acidic. Sprigs & Twigs can perform the soil test. Cool season grass pH should be 6.5-6.8. Once the pH is suitable, over seed your lawn in the fall to get more cool season grasses growing to provide crabgrass control for the following year.

I thank our colleagues at PJC Organic, Rowley MA for their contribution to this answer.

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About Linda Lillie

Linda K. Lillie is the President of Sprigs & Twigs, Inc, the premier landscape design and maintenance, tree care, lawn care, stonework, and carpentry service provider in southeastern Connecticut since 1997. She is a graduate of Connecticut College in Botany, a Connecticut Master Gardener and a national award winning landscape designer for her landscape design and landscape installation work.


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