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 refers to the practice of planting different crops in close proximity to each other to enhance nutrient uptake, provide pest control, encourage pollination, and increase crop production. While scientists refer to the idea of companion planting as "pseudoscientific," as it hasn't been scientifically validated, many experienced gardeners vouch for their carefully compiled lists of 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 with some success. However there are a lot of variables that can impact the effectiveness of plant companions.
Luckily, tomatoes make good companions with many popular garden vegetables. Some companion plants reportedly help boost the health and vigor of the tomato plants, some improve the tomato flavor, and other companion plants allegedly repel and deter insect pests and diseases. You are 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 Plants
A lot of plants are touted as improving the health, vigor, and flavor of tomatoes. All of these features are hard to measure, since little scientific research exists to back up the claims, and many other factors may be involved. Still, it is interesting to try them out in your own garden.
Plants recommended for companion planting with tomatoes include amaranth, asparagus, basil, beans, borage, calendula (pot marigold), carrots, celery, chive, cleome, cosmos, cucumber, garlic, lemon balm, lettuce, marigold, mint, nasturtium, onion, parsley, sage, and squash.
- Amaranth helps repel pests by attracting predatory beneficial insects.
- Basil repels insects, improves growth, and enhances flavor. Repels mosquitoes and flies (even fruit flies).
- Borage improves growth and flavor and repels tomato hornworms.
- Bee balm, chives, mint, lemon balm, and parsley improve health and flavor. Be careful when companion planting bee balm, lemon balm, and mint, as they can become invasive.
- Carrots planted near tomatoes help loosen soil. If planted too closely, the carrots may not get as large as they should, but they will still taste good.
- Garlic repels red spider mites. Garlic sprays help control late blight.
- Lettuce appreciates some shade when weather warms. It not only benefits by being planted in the shade of taller tomato plants, but it provides a living mulch--helping to keep the soil cool and moist.
- Marigolds repel pests and reduce root-knot nematodes in soil.
- Nasturtium not only looks lovely planted with tomatoes, but it also serves as a trap crop for aphids. Plus, it's an edible flower, making a pretty--and tasty--addition to salads.
Bad Companions for Tomatoes
- Cabbage (Brassica) family: All relatives of cabbage stunt the growth of tomato plants (including broccoli, Brussels sprouts, cabbage, collards, cauliflower, kale, kohlrabi, rutabaga, and turnip).
- Corn: The corn earworm is the same as the tomato fruitworm (larva Helicoverpa zea). Growing the plants in proximity that are susceptible to the same pests can invite disaster and a decimated garden.
- Dill: Mature dill plants 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 nightshade family like tomatoes and are all susceptible to early and late blight, which can 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 three years. Hornworms (Manduca quinquemaculata, the larva stage of the 5-spotted hawkmoth) love the foliage and fruit of tomatoes, peppers, and eggplants and can quickly decimate plants. Also, planting tomatoes near potatoes can make the potatoes more susceptible to potato blight.
- Fennel: Fennel secretes a substance from its roots that inhibits tomato plant growth. This secretion affects many other garden plants, too.
- Walnuts: Do not 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 Can Help These Plants
- Asparagus: Tomatoes repel the asparagus beetle.
- Gooseberries: The scent from interplanted tomatoes helps repel insect pests.
- Roses: Tomatoes can protect roses from black spot. You can interplant or use a spray. To make a spray, liquify tomato leaves and then dilute them with 4 to 5 pints of water. Add a tablespoon of cornstarch. Use the spray on rose leaves, if you cannot plant tomatoes next to them. Some believe that It could be the cornstarch that does the trick here.
Good Resources on Companion Planting
If you are interested in learning more about companion planting, you might want to look at two great books on the subject: Carrots Love Tomatoes by Louise Riotte and Great Garden Companions by Sally Jean Cunningham.
Carrots Love Tomatoes helped make the idea of companion planting popular. Riotte extensively studied all types of plants from vegetables to weeds. This book could be used as a classroom text.
Cunningham's book, written more casually, is jam-packed with information. The book focuses on the vegetable garden. Cunningham groups her vegetables into neighborhoods and makes pairing appropriate companions a bit easier.
Insectary Plants: Flower Power for Natural Enemies of Vegetable Pests. Northeast Sustainable Agriculture Research and Education
Ahmad, Hasib, Kobayashi, Manami, Matsubara, Yoh-ichi. Changes in Secondary Metabolites and Free Amino Acid Content in Tomato with Lamiaceae Herbs Companion Planting. American Journal of Plant Sciences, 11,12, 2020, doi:10.4236/ajps.2020.1112134
Best of Enemies; A Brief Guide to Companion Planting - Part 2. University of Arizona Agriculture and Life Sciences Cooperative Extension
Companion Planting. Cornell University Cooperative Extension Chemung County
Marigolds (Tagetes spp.) For Nematode Management. University of Florida Institute of Food and Agricultural Science
Herb Gardening. Colorado State University Extension
Black Walnut Toxicity. Purdue University Cooperative Extension Service