Weed killers are best applied a little later in the spring than crabgrass preventer. The reason for this is that weed killer, whether liquid or granular weed and feed, is absorbed through the leaves of the plants and not at all through the roots. The fact that weed killer only enters the plant through the leaves makes it very important that the product not be washed off for at least 48 hours after application. The rate at which the weed killer is absorbed is determined by how rapidly the plant is growing and it its best to wait until the weeds are growing well before applying the weed killer.
Hints for success with weed killers
- Apply granular weed killers and weed and feeds when the lawn is already damp. Lightly pre-moisten the lawn or apply in the morning when there is dew on the lawn. This will help the weed killer granules stick to the leaves and increase effectiveness.
- Add a few drops of liquid detergent to liquid weed killers. This will help the herbicide coat the leaves of the weeds and increase effectiveness.
- Weed killer and weed and feeds should not be watered in or rained on for at least 48 hours after application. If it is it will not be effective.
- Do not apply weed killers when temperatures are expected to be above 85 degrees.
- Do not mow the lawn just prior to application. Mowing removes the leaves of the weeds that absorb the weed killer.