I am presently growing radishes next to (very close) shallots AND garlic (albeit not onions); I have grown my tomatoes and peppers within 6' of each other every year for many years. I alternate stuff throughout the garden year after year, growing peppers where tomatoes were and vice versa. I have a small garden, 10 X 20' and no place else to grow it. I re-apply major compost each year. I would be interested in reading your source on this info since my stuff seems to be doing OK. Willing to learn!