The type determines when to apply an herbicide. Pre-emergents are usually applied in late winter or early spring, while post-emergents are applied in spring after the weeds begin to grow. When using herbicide in gardens, take care to protect the plants you don't want to kill.

What is the most effective time to apply herbicide?

The best time of year to use weed killer is Spring, followed by Fall. Spring is an effective time for catching weeds in their pre-growth season, in order to prevent them from sprouting. Fall is similarly effective because, ahead of the Winter, this is when weeds are most vulnerable.

When should you not use herbicide?

It is not recommended you apply an herbicide at all when temperatures exceed 85 degrees as the herbicide will damage your grass. It is best to wait until it gets cooler and apply a post-emergent herbicide to any weeds that are currently in your yard.