If I use Roundup® to kill my existing grass, how long after the application must I wait before I put grass seed down?

Roundup is a broad spectrum herbicide. That means it should kill any actively growing plant which absorbs the chemical. It is appealing to use during lawn renovations because re-seeding can occur within a short time after the chemical has been applied and it will not harm the germinating grass seedlings. Wait at least five days or until you see that the area sprayed with Roundup has died. If you see any areas that do not look as if they were killed by the first application, a second application would be recommended. It is always important to follow label instructions when using any hericide.