 Is it true that it can be too warm and weeds will shut down when it's hot? Well, weeds will shut down just like your grass will shut down, though, really. But they won't go away. I mean, the weed seeds are there. They'll come back. Just like if we get rain again or like if you've let your lawn go when you haven't watered it when it's been really hot. Once we get rain or once you start watering it, it'll come back. It won't go away on its own.