When to Put Weed Killer on a Lawn

Weeds kill grass, destroying the beauty of your lawn. Weed killers tackle the problem, but you need to know when to use weed killer to ensure maximum success against pesky, sometimes resilient, weed problems. Knowing when to apply weed killer also ensures you do not harm your lawn grass, the family pet or humans.

When you apply weed killer depends largely on the type of weed killer that you want to apply. The best time to apply weed killer is in late spring. This generally occurs from early May to early June in much of the U.S. Late spring is a good time to apply weed killer because weeds are still young at that point and are less able to fight the effects of the herbicide. Some weeds, though, grow best in warmer or cooler conditions. Be prepared to use a spot-treatment weed killer throughout the year. This type of herbicidal product targets weeds directly via a spray application. Spot treatment also is best when plants have germinated. To tackle weed problems before they occur, you can use a pre-emergent weed killer after the last mowing in the fall or in early spring.

Weather plays a key role in the success of any weed killer application. Apply weed killer when you don't expect rain for 48 hours. Most weed killers destroy weeds through direct contact. The chemical soaks into the leafy surface of the weed. Rain causes weed killer to wash away before it is able to soak into the plant. Granular weed killers, though, benefit from a soil that is slightly damp. Thus, you should water your lawn lightly or wait for a light rain before applying granular weed killers. It is also best to apply spray weed killers when there is minimal wind. Wind causes spray weed killer to drift into unintended areas. If exposed to the blowing spray, patches of lawn might die.

Herbicidal weed killers work by attacking the plants. To maximize their impact, do not mow or prune for 5 days before applying weed killer. This increases the leafy surface of the weeds, which improves the application of the weed killer. You also do not want to mow for 2 days after applying weed killer to allow the plant time to absorb the product. If you mow on a weekly cycle, you might want simply to skip a week.

Weed killer is harmful to grass seedlings. Do not apply weed killer on your lawn if your grass is not mature and avoid applying it to patches where you have reseeded. Target your application for a time when pets and children do not intend to be on the lawn. Keep children and pets away from a treated lawn for 48 hours.