Q: In early October I completely killed my front lawn and reseeded. The grass is coming in great. However, along with the grass, I have a lot of what looks like henbit weed coming in. How long should I wait before applying broadleaf weedkiller?
A: My rule of thumb is to wait at least until you’ve mowed the lawn twice.
This would be the stage at which the seedlings have begun to develop a strong root system and can withstand the effect of a herbicide.
I know you had to initially choose between seeding and applying a pre-emergent but you can consider putting out a pre-emergent weed preventer in mid-November.
You’ll only get fifty percent weed control at this point in the season but that, combined with a regular program of light over-the-top weed sprays, will eliminate a big portion of your broadleaf weed problem.