The pairs most often listed as poor neighbors are onions or garlic with beans, peas or lettuce; tomatoes with potatoes, corn, fennel or cabbage-family crops; and potatoes with squash or cucumbers. Our chart below lists all 16 keep-apart pairs we track.
Companion planting usually gets explained as "who grows well together." The other half of the question is often more useful when you only have one or two beds: which vegetables should not be planted together? Here is the list, grouped so it is easy to remember, plus the reasons where they are known.
Onions and garlic vs. beans, peas and lettuce
The onion family causes the most conflicts in a small garden because onions and garlic are listed as companions for so many other crops (tomatoes, carrots, peppers, cabbage) yet as poor neighbors for legumes and lettuce.
| Plant | Keep away from | Notes |
|---|---|---|
| Bean | Onion | Onion family is listed as incompatible with beans. |
| Bean | Garlic | Garlic is listed as incompatible with beans. |
| Pea | Onion | Onion family is listed as incompatible with peas. |
| Pea | Garlic | Onion family is listed as incompatible with peas. |
| Lettuce | Onion | Onion family is listed as incompatible with lettuce. |
| Lettuce | Garlic | Garlic is listed as incompatible with lettuce. |
Full chart: vegetables to keep apart
| Plant | Keep away from | Notes |
|---|---|---|
| Pea | Potato | Listed as incompatible. |
| Bean | Beet | Beets are listed as incompatible with pole beans. |
| Tomato | Potato | Same family; attacked by the same pests and diseases. |
| Tomato | Corn | Listed as incompatible. |
| Tomato | Fennel | Listed as incompatible. |
| Tomato | Cabbage family | Listed as incompatible. |
| Potato | Squash / zucchini | Listed as incompatible. |
| Potato | Cucumber | Listed as incompatible. |
| Carrot | Dill | Listed as incompatible. |
| Cabbage family | Strawberry | Listed as incompatible. |
Why some of these pairs clash
- Shared pests and diseases. Tomatoes and potatoes are both nightshades and share blights. Corn earworm and tomato fruitworm are the same insect.
- Competition. Sprawling squash and cucumber vines crowd potatoes, which need room to hill and dig.
- Different seasons. Cabbage-family crops are cool-season plants; tomatoes are warm-season. Sharing a bed often means one is struggling or in the way.
- Reasons unknown. For some listed pairs the source gives no mechanism. We include them because the source lists them, but treat them as cautions, not rules.
Where sources disagree
A few pairs are listed as good by one extension service and bad by another. If you like the combination, try it and watch.
| Plant | Partner | What the sources say |
|---|---|---|
| Carrot | Radish | UMD suggests sowing them together and pulling radishes early; VCE lists radish as incompatible with carrots. |
| Cabbage family | Dill | PSU: dill deters cabbageworm egg-laying; VCE lists dill as incompatible with cabbage family. |
| Cabbage family | Spinach | VCE lists spinach as a cabbage companion in one row and cabbage as incompatible with spinach in another. |
Think in plant families
A handy shortcut: plants in the same family tend to share pests and diseases, so most gardeners rotate by family, moving each group to a different bed every year.
| Family | Common crops |
|---|---|
| Nightshades | Tomato, pepper, eggplant, potato |
| Cucurbits | Cucumber, squash, zucchini, melon, pumpkin |
| Brassicas | Cabbage, broccoli, kale, cauliflower, radish |
| Alliums | Onion, garlic, leek, chives |
| Legumes | Bean, pea |
| Carrot family | Carrot, dill, fennel, parsley, cilantro |
What matters more than any list
- Sun.
Most vegetables want 6–8 hours of direct sun. Put tall crops on the north side so they do not shade short ones.
- Spacing.
Crowding causes more trouble than bad companions: it cuts airflow and invites disease.
- Black walnut trees.
Juglone from black walnut roots and leaves harms tomatoes, peppers, potatoes and eggplant. Keep sensitive crops well away.
- Rotation.
Do not plant the same family in the same spot year after year.
Planning a specific bed? See what to plant with tomatoes, our raised bed layouts, or the full companion planting chart.
Pick your plants and spot every keep-apart pair before you plant.
Open itSources
- Virginia Cooperative Extension, "Companion Planting in Gardening" (SPES-620P)
- University of Maryland Extension, "Vegetable Succession and Companion Planting"
- Oregon State University Extension, "Companion Planting"
- Penn State Extension, "Herbs Make Good Plant Partners and Companions"
- University of Minnesota Extension, "Planting the vegetable garden"
- USDA Plant Hardiness Zone Map
- NOAA NCEI U.S. Climate Normals (frost/freeze data)
- University of Wisconsin–Madison Extension, "Black Walnut Toxicity"
Pairings are summarized in our own words from extension-service guidance. Research support for many companion effects is limited, so treat them as good habits, not guarantees.