Applying a weed and feed product to your lawn may seem like a perfect way to kill two birds with one stone. Not only are you able to get rid of pesky weeds, but the fertilizer contained in the product also will help the grass to thrive. Weed and feed products aren't ideal for all situations, though, and may cause some problems if you plan to reseed the lawn soon after their application.
What Is Weed & Feed?
As the name implies, weed and feed products contain both a fertilizer and an herbicide to control weeds while feeding the surrounding grass. If the lawn has grass that is already established, this works well. Ideally the product should be applied a few weeks after the final frost once the grass and weeds are visibly growing because applying the product on dormant weeds will have no effect. Apply it periodically throughout the rest of the year as well to keep weeds under control.
Most weed and feed products come in granule form, and you should apply them to damp grass to ensure activation. For best results, mow two to four days before application and apply weed and feed products when no additional rain is expected for at least 48 hours. After application, do not mow the treated grass for at least seven days to allow the herbicide time to work.
Hindering New Growth
Weed and feed products work by preventing new growth, effectively stopping weed seeds from sprouting and newly sprouted weeds from flourishing. The herbicides used aren't specific enough to only target weeds, however; they'll do the same to grass seeds and any new grass growth. It can take up to four weeks for the herbicide effect to fade, so sowing grass soon after applying weed and feed is likely futile because new grass won't be able to grow.
When to Sow Seed
If you must sow grass seed after applying weed and feed, wait at least four to six weeks before doing so to ensure the herbicide won't prevent the seeds from sprouting. Ideally you should sow seeds in the fall far enough in advance of frost that the new grass will have several weeks to start growing before going dormant. You can also sow grass seed in the early spring, though if you do so you should hold off on applying weed and feed for at least four to eight weeks to ensure it doesn't damage the young grass.