My sunflower patch is being eaten alive by (I'm pretty sure) ants. I tried a water/soap mix, but it doesn't seem to stop the ants at all. Any suggestions? The spot where the flowers are is near a sidewalk where there seem to be many anthills, with no grass or anything between my garden and the concrete. I'm going to have to start some of the sunflowers over again, since a few have been reduced to skeletons!