All the companion planting guides say to keep these three well away from each other. I can understand that, as they all grow the same way. The question is, how far away from each other? I've got dill in the herb bed next to the house. I just planted fennel on the edge of one of the garden beds. Those two I'm okay with. But now, I want to plant some caraway. Is 15' away from the dill enough? Is about 30' away from the fennel much better?