There are plants that work well together and plants that should be kept apart. Matching the two groups into a garden plan is often difficult, especially in a small space. Companion planting tomatoes is a lot easier than trying to lay out your entire vegetable garden with good companions.
Companion planting is part experience, part folklore and part wishful thinking. Most companion planting teachings are passed down by gardeners who experimented with pairing plants and had some success. However there are a lot of things that can impact the effectiveness of plant companions, so don't expect magic.
Luckily tomatoes make good companions with the majority of popular garden vegetables. Some companion plants help improve the health and vigor of the tomato plants, some improve the tomato flavor and other companion plants are used to repel and deter insect pests and diseases. You're probably going to grow some of these plants anyway, so why not experiment on your own and use some of them as companion plants for your tomatoes.
Good Tomato Companion PlantsA lot of plants are touted as improving the health, vigor and/or flavor of tomatoes. All of these features are hard to measure, little scientific research has actually been done to back up the claims and many other factors may be involved. Still, it's interesting to try them out in your own garden.
Plants Recommended for Companion Planting with Tomatoes: amaranth, asparagus, basil, bean, calendula (pot marigold), carrots, celery, chive, cleome, cosmos, cucumber, garlic, lemon balm, lettuce, marigold, mint, nasturtium, onion, parsley, peas, sage, stinging nettle and sow thistle.
- Amaranth helps repel insects.
Basil repels insects and disease, improves growth and flavor. Repels mosquitoes and flies (even fruit flies).
Borage improves growth and flavor and repels tomato worms. (I've not found this to be true.)
- Bee balm, chives, dill, mint and parsley improve health and flavor. Use dill early since mature dill starts to inhibit tomato growth.
- Carrots planted near tomatoes may not get as large as they should, but they'll still taste good.
Garlic repels red spider mites. Garlic sprays help control late blight.
- Stinging nettle nearby improves taste.
- Sow thistle aids growth.
Bad Companions for Tomatoes
Cabbage (Brassica) Family - All relatives of cabbage stunt the growth of tomato plants, (incl: broccoli, Brussels sprouts, cabbage, collards, cauliflower, kale, kohlrabi, rutabaga, turnip).
Corn - The corn earworm is the same as the tomato fruitworm. (Also known as the cotton bollworm.)
Dill - Mature dill plants, as mentioned above, will start to inhibit tomato plant growth. Plant the dill you want to go to seed away from your tomatoes.
Eggplant, Peppers and Potatoes - These plants are in the same family as tomatoes and are all susceptible to early and late blight, which will build up in the soil and get worse each year. Avoid planting them near each other or in place of each other for at least 3 years. Also planting tomatoes near potatoes can make the potatoes more susceptible to potato blight.
Fennel - Inhibits tomato plant growth.
- Walnuts - Don't plant tomatoes under walnut or butternut trees, which produce an allelopathic chemical called juglone that inhibits the growth of tomatoes (and all the members of the nightshade family). Tomatoes are also susceptible to the disease walnut wilt.
Tomatoes Help Protect and Make Good Companions with These Plants
Asparagus - Tomatoes repel asparagus beetle.
Gooseberries - The scent from interplanted tomatoes helps repel insect pests.
- Roses - Protects roses from black spot. You can interplant or use a spray. Spray: Liquify tomato leaves and then dilute them with 4-5 pints of water Add a tablespoon of cornstarch. Use to spray on rose leaves, when you can't plant tomatoes next to them. NOTE: It could be the cornstarch that does the trick here. Recent studies are showing cornmeal is an effective fungicide on tomatoes.
Further Reading on Companion Planting
If you're interested in reading more about companion planting, two of my favorite books on the subject are:
Carrots Love Tomatoes, by Louise Riotte
This book helped make the idea of companion planting popular. Ms. Riotte has made an extensive study of all types of plants, from vegetables to weeds. This book could be used as a classroom text.
Great Garden Companions, by Sally Jean Cunninghamn
Ms. Cunningham uses a more casual writing style, but her book is just as information packed. The focus here is the vegetable garden and Ms. Cunningham groups her vegetables into neighborhoods, making pairing appropriate companions a bit easier.