Using herbs and flowers in this way can keep your garden "green" and prevent tears when you find your prized tomato plant cut off at the root by some nasty bug!
Petunias, marigolds and geraniums can be planted in a border around the garden or trees. If you want the benefit of catnip without digging it out of your garden for years to come, put in a large clay pot and place nearby. For other pest preventers, thoughtful interplanting of vegetables can help with the process.
Underlined items can be found at Beier's Greenhouse.
Ants:Pennyroyal, spearmint, southernwood, tansy
Aphids: Garlic, chives and other onions, coriander, anise, nasturtium a...
Mulching around tomatoes is perhaps the most overlooked (and important) part of growing quality tomato plants. Mulching with (herbicide-free) grass clippings, straw, or fabric will not only keep the weeds out, but also prevent blight. Tomato Blights live in the soil and hurt the plants when that soil bounces up and hits the bottom leaves. Mulching around the stalk and out a few feet will help to prevent blight from ruining your crop.
What's wrong with my tomatoes?
By no means is this a complete list of tomato problems, but knowing a little information about tomatoes now can prevent a lot of google searches...