Roundup – Use In Cold
Q: Is it too cold for Roundup to kill the weeds now growing in my flower beds?
A: The leaves on the weeds you aim to control should be actively photosynthesizing when glyphosate (Roundup, etc) is applied. That means the air temperature should be above 50 degrees. You may get some control at lower temperatures so experiment by spraying the weeds on a sunny day and see what happens. In cold weather, don’t expect results for two weeks.