People often ask when they should spread crabgrass preventer. That is a hard question. If we have a warm early spring it needs to be put on earlier. You have probably heard the rule of thumb, put crabgrass preventer on before the Red Buds bloom. That is probably ok. That always seems a little on the late side.
If you have a protected area on the south side of a brick building, for example, that area may germinate well before the Red Bud's bloom, because the soil temperatures will be much warmer there. A good time would be after you mow your grass for the first time, around the middle of March.
There are mainly two kinds of crabgrass preventer: Barricade and Dimension. There are different names for these but they all work the same.
Barricade is a longer lasting preventer. It is often considered the best choice of the two. Barricade is only a pre-emergent, meaning it will only stop crabgrass before it germinates.
Dimension prevents germination but it also will kill very small crabgrass. So Dimension can be used if you are a procrastinator or you just didn't think of it in time. If you think it is probably too late to spread crabgrass preventer, spread Dimension. Another negative to Dimension is, it does not have quite as good of control later on in the summer when all pre-emergents are running out of umph.
Remember, crabgrass preventer stops grass seed from germinating. Not just weedy grass, good grass too. So spring is a poor time to overseed your lawn. If you do overseed, your lawn can not be treated for crabgrass for 6 to 8 weeks and by then crabgrass will likely have germinated.