Not a stupid question. If your spouse and wallet are ok with it then go for it. Some pre-emergents last longer/shorter than others. Most of the time you can get away with three if you time it right. For me that is usually mid/late feb, beg/mid may then mid/late sept.

Thanks for the reply. I know the best defense against weeds is a healthy, dense turf, but the more I read the more I realize that apparently there are all types of weeds trying to grow at any given time. Some in spring, some in fall, some in summer or winter. Every 90 days would be 4 applications per year, so I don't think it would be too bad. Thanks again for the help. I just wasn't sure if there would be any negative effects to doing that as it seems most people only apply a pre-emergent in the early spring and fall.

I agree. Not a stupid question, but nobody seems to ask it. They talk about preemergents as if it were a one-time thing. Uh, no, it's not. I refuse to go down that road. I'm working on dense grass.

Yeah that's what I'm going to work towards as well, just want to protect my lawn for the first year or two after I seed and until the turf gets dense. From what I read it takes around 3 years to get a really good, dense, turf. Thanks for the reply.

I talked to a guy once at one of the box stores about Pre-emergent applications. He said there is not a date specific, but just had to do with ground temps. I think he said 65 degrees, above which which the pre-emergent just doesn't work anymore.

Very cold here still, zone 6.