We recently seeded our backyard put compost down as topsoil b/c all we had was sand. It's a very large backyard and used about 3-4 semi trailer size trucks full of dirt. We layed seed about 3-4 weeks ago and have been trying to water for the last several weeks, since the yard is so big it's hard to keep it all wet. The weeds are growing instead. It's green out there, but mostly weeds. Is there something out there that we can use that will kill the weeds but not the grass? Any help would be great,

Thanks,

Brenda