Preventing Crab Grass
Crab Grass Prevention is the number one way to stop this weed from overtaking your lawn and destroying it. However, to prevent something, you must first understand it. How it grows, what it needs to survive, and where it grows. Understanding crab grass is the first step to preventing it.
What is Crab Grass?
Crab grass is well known by its name, but little known by sight. It has been confused with other weeds such as tall fescue, timothy, and nimblewill. It is a summer annual weed which means that it will germinate in the spring, grow through the summer, produce seeds in late summer, and die when we get our first frost.
Crab grass starts to germinate when soil temperatures in the spring maintain a temp. of 55 to 60 degrees for a period of 3 or more days (at 2-3" below the surface).
After germinating seeds sprout, the plants increase in size by tillering. Complete ground cover may result from only two or three plants per square yard. Where tillers or culms touch the soil, rooting will occur at the nodes. Seeds will start to appear within 40 - 50 days after germination and will continue until frost. Seed production is prolific. With significant space allowed for full sized plant growth, seeds produced per plant averages 180,000 for large crab grass and 150,000 for small crab grass. This averages out to about 10,000 - 20,000 seeds per square foot. Seeds will not germinate in the same year they are produced. They will lie dormant over winter and sprout the following spring. Some seeds can lie dormant for many years.
When a lawn thins out from disease, insects, low fertility, drought, low mowing, or poor drainage crab grass is one of the first weeds to invade. For this reason the best way to control crab grass is to have a thick healthy lawn.
You can kill crab grass by using pre emergence herbicides.
The other form of crab grass prevention is by the use of pre emergence herbicides. Pre emergence herbicides establish a short lived barrier just below the surface of the soil which kills the crab grass seedlings just as they begin to grow. The timing of this application is what is crucial. Pre emergence herbicides must be applied before the soil temperature reaches the ideal temperature for crab grass to begin germinating. (see above) A good rule of thumb for the timing of this application is to apply about the time that the forsythia blooms drop. This is also about the time that the lilacs are starting to bloom.