- Crabgrass is a non-native import that has few natural enemies on the North American continent. It thrives in almost any climate or soil condition and gets its name from its habit of sending out runners above and below the soil in such a way that it resembles a crab. Consequently, when you attempt to pull or dig up crabgrass plants in a patch, you will find yourself doing battle with an interconnected series of plants that hampers the removal of even one. Worse yet, it will be intimately entwined with your lawn grass, so you end up pulling that out as well. Many of the strategies that work to keep other weeds down, like regular mowing to chop off the seed-bearing heads, do not work on crabgrass. Crabgrass does most of its growing sideways and probably grows at a lower level than your lawn grass.
- While the ground-hugging growth habit of crabgrass is one of its chief strengths, this is also a weakness, as it is a sun-loving plant. Another weakness is that, in colder climates, it is an annual, so you'll get another shot at it after it dies down in the fall.
If you keep your lawn grass thick and healthy, and mow it high to deprive the crabgrass seedlings of light and air, the crabgrass will not thrive. Like any sun-loving plant, it will be spindly and pale when shaded, and a solid forest of well-established lawn grasses will tie up the vital nutrients it needs to survive the seedling stage. Mowing a lawn too short is considered the chief cause of crabgrass infestation.
In general, mow lawn grasses at about 3 inches for good crabgrass control. This height will also impair development of other types of weeds and slow down evaporative water loss. Make sure you have no bare patches on your lawn, as a sunny spot with no competition will encourage crabgrass growth and it will immediately invade the healthy parts of your lawn.
If your crabgrass has been unchecked so long that it owns large areas of your yard, you may not have enough lawn grass to combat it. In this case, you may have to cede the field of battle until this year's infestation dies down. After that, waste no time making sure that your lawn grasses are thick, healthy and tall before the crabgrass season starts again. - Among the few lawn grasses that can successfully win back territory from crabgrass are Bermuda and zoysia grasses. They have the same growth habit as crabgrass and are just as invasive. If you handicap the crabgrass by pulling up a fair amount, these grasses will spread and choke it out.
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