- 1). Apply pre-emergent herbicides about two weeks before crabgrass appears. For many parts of the United States and Canada, that means you will apply the product in late April to early May. You can also reapply as crabgrass begins to appear, because the seeds won't germinate all at the same time. This won't harm any established grass, but it will stop new grass from growing.
- 2). Use post-emergent herbicides after crabgrass is well established, usually by late July or August. These are not as effective in controlling crabgrass as other methods, however, and may also cause temporary browning of the lawn.
- 3). Mow your lawn frequently and leave the grass long---at a height of 2 or 3 inches. Crabgrass doesn't grow in cool conditions.
- 4). Water consistently and heavily all season. Your grass needs between 1 and 1 1/2 inches of water every week, preferably all at once, rather than sprinkled over several days.
- 5). Use a dethatching rake to remove most of the crabgrass when it becomes thick. This helps prepare the ground for seeding.
- 6). Fertilize in the fall, or in early spring. Fertilizing over the summer benefits the crabgrass more than it will your lawn. Overseed in late summer, shortly before crabgrass is killed by the frost.
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