If the weeds are already there, then it's too late for thse pre-emergents. That should have been put in 2 months ago. You'll have to treat the weeds now with some other form of weed killer. But, as weeds go, not all sprout now, you can use pre-emergents for the others.

I plant tomatoes around a buried five gallon bucket with holes around the bottom .For deep root watering.I usally put five plants around one bucket and in the heat of summer only water ever three days. I usally plant 35 tomatoe plants and last year was a bad year and still produced close to 300 lbs . Put a lid on the bucket and drill a few holes for over flow. Drill a 1"1/2 in the middle to stick a piece of 1"1'4 pvc that is about 5' long to water thru. I use 6"x6" concrete wire for a cage that is cut 10' long .That will make 3' wide cage. I plant the buckets 6' apart. So my tomatoes take up a space that is 3' wide x 42' long. And most years my plants are close to 6' to 8' tall come frost.

What all do you have out in the garden now?

Me, I just have onions and Roamine Lettuce I planted too early and are frost bit. Got to start over on them.

Onions , Buttercrunch lettuce , radishes , collards and Bok-choi ( Chinese cabbage) . Turnips haven't sprouted yet but I have tomatoes and chilis in the house.