That's the only problem with using sod, and that's when wild seed lands on top, and lie dormant waiting for just the right conditions and boom Weeds! The best way to keep them down is to use a grass catcher on your mower and bag all the seeds before they fall back on the turf. Mow often to keep the tops for sprouting into flowers. Here we use a broadleaf weed control product called 2-4-D but you have to be careful because it will damage some grasses. Keep it mowed often. The other option is to hand pull by hand.