apply the crab grass killer in early spring (March) If memory serves
when the temp is between 50 - 55 degrees.
Killing Clovers: Can be done almost anytime. I use a broad leave killer
from Lesco. basically you wet the grass with the sprinklers, apply the
Broad leave Herbicide, make sure it stays dry for 3 days and it goes
away. In the fall make sure you seed to thicken up the yard. Thick grass
helps prevent weeds from growing in the first place