How Long Should I Wait To Spray Weed Killer After Seeding Lawn?

Q: I reseeded my fescue lawn and the new grass is coming up really good. There are a lot of weeds coming up with the new grass. How long should I wait to spray weed killer after seeding the lawn? 

A: If you disturbed the soil before you reseeded, I can understand why you have weeds now. But tilling or aerating can’t be avoided. Weed seeds lie dormant in the soil for several years and only sprout if brought to the surface. The label on broadleaf weed killers typically says not to use the product on a newly seeded lawn until it has been mowed three times. Be patient; you don’t want your weed control attempts to harm the grass you spent so much time planting.