Well, I always plant my carrots with my onions and I plant flowers near my runner beans. Onions are meant to stop the carrot fly and the flowers I plant near the beans to attract the bees so they pollinate the flowers on the beans. Never plant potatoes near my tomatoes as they both get blight, so if my potatoes get it hopefully I can conain my tomatoes and treat them before they get it.
You should always rotate your vegtables, every year, as disease easily builds up in the ground. I hate club root, so always treat your brassica's before planting.
