Ants

I have a lot of black ants in my yard. When we cleared a spot for a vegetable garden, I found ants living in the soil - I planted a few veggies anyway, and my tomatoes are growing nicely, but the ants are attacking the corn!

Also dug up a flower bed and found yet more ants.

I'd rather use something organic than chemical. I tried corn meal, but that doesn't seem to have helped. Sprayed some chemical stuff I found in Wal-Mart, and that seemed to control the ant population a bit - at least, they're no longer coming into the house, but there's still a good number in my garden.

I need some suggestions, please!

Thanks!