I've wondered for a long time how far away to plant "negative pairs" (Pairs of plants that DON'T go well together), and I have I had a lot of trouble finding ANY information on this. So I decided to try to figure this out another way. I figured the answer would probably involve the reasons that they were not good to plant together. I found the following common reasons:

A Attracts harmful bugs or fungi
B Competes for same nutrients in soil
C Makes soil uninhabitable for plant (fixing too much of a nutrient in soil, for instance)
D Detracts from flavor
E Stunts growth
F Cross Polinates With Each Other

I'm guessing that for reasons B, C, and probably D and E that the amount you would need to plant them away from each other would be at least further than their root width. How much space past the root width do you think I should allow? (A few inches, a foot, a few foot?)

Oh, and here's a site that lists root width on a lot of common vegetalbes:

http://www.waldeneffect.org/blog/Plant_spacing_and_vegetable_roots/

I figure things that cross politate (like carrots and dill) would only be an issue if you planned to collect seed. Again, if you did plan to collect seed, I'm not sure how far apart you'ld need to go, but I'm guessing it might be a fairly good distance. Any ideas?

I'm not sure how far away to plant things that attract similar bugs and would love to hear your thoughts on this, too.

If you see any holes in my theories, or have any thoughts related to this, I'd love to hear it. Thanks so much in advance! I