Companion planting isn’t only about which plants help each other. Some plants make poor neighbors: they compete for the same nutrients, attract the same pests, spread the same diseases or simply crowd each other out.
Here are 10 common pairs to keep apart in your vegetable garden, with the reason for each so you can plan smarter beds.
10 Plant Pairs to Keep Apart
1. Tomatoes and potatoes
Both are in the nightshade family and both get early and late blight. Planting them side by side lets disease move easily between them. Keep them in separate beds, and don’t plant either where the other grew last year.
2. Tomatoes and corn
The corn earworm is the same insect as the tomato fruitworm. Growing both together gives this pest two favorite crops in one spot.
3. Beans and onions (or garlic)
Beans and peas are widely reported to grow poorly next to onions, garlic, leeks and chives. Keep the onion family on the other side of the bed.
4. Peas and onions
The same goes for peas. Give them a spot away from alliums, and plant them with carrots, radishes or lettuce instead.
5. Cabbage family and tomatoes
Broccoli, cabbage, cauliflower and kale are heavy feeders. Next to tomatoes, both crops compete hard for nutrients and water.
6. Cucumbers and potatoes
Potatoes can make cucumbers more prone to blight, and both like plenty of water and nutrients. Give each its own space.
7. Squash and potatoes
Squash and zucchini sprawl over potato plants and compete for the same resources. Disease can spread more easily in the crowded, damp conditions.
8. Carrots and dill
Carrots and dill belong to the same plant family and attract the same pests. Mature dill may also hold back carrot growth. Plant dill elsewhere in the garden, where its flowers can still feed beneficial insects.
9. Fennel and almost everything
Fennel slows the growth of many vegetables nearby, including beans and tomatoes. Grow it in a container or a separate corner of the garden.
10. Sunflowers and potatoes
Sunflowers can release compounds that hold back the growth of some plants, and their size means they shade and outcompete smaller crops. Grow them at the north edge of the garden.
Quick Reference: Plants to Keep Apart
| Plant | Keep away from | Why |
|---|---|---|
| Tomato | Potato, corn, cabbage family, fennel | Shared diseases and pests; competition |
| Beans & peas | Onion, garlic, leek, chives | Reported poor growth |
| Cucumber | Potato, sage | Blight risk; competition |
| Squash | Potato | Crowding and competition |
| Carrot | Dill, parsnip | Same family; shared pests |
| Cabbage family | Tomato, pepper, strawberries | Heavy feeders compete |
| Potato | Tomato, cucumber, squash, sunflower | Blight; crowding |
| Fennel | Most vegetables | Slows nearby growth |
Simple Rules to Avoid Bad Pairings
- Separate plant families that share diseases. Keep tomatoes, potatoes, peppers and eggplant away from one another’s old spots.
- Don’t crowd heavy feeders. Spread out tomatoes, corn, squash and the cabbage family, and add compost.
- Watch the shade. Plant tall crops on the north side so they don’t block the sun from short ones.
- Rotate every year. Moving crops to a new bed each season breaks pest and disease cycles.
Good to know: many “bad pairing” lists come from gardeners’ experience rather than controlled studies. The most reliable reasons to separate plants are shared diseases, shared pests and competition for light, water and nutrients.
Now that you know what to avoid, see the companion planting chart for vegetables, the best companion plants for tomatoes, and how to plant a Three Sisters garden.
Frequently Asked Questions
What happens if I plant bad companions together?
Usually nothing dramatic. You may see smaller harvests, more pests or faster disease spread. Move the plants apart next season.
Can tomatoes and peppers grow together?
Yes. They’re good neighbors with similar needs. Just rotate them together, because they share some diseases.
Is it bad to plant onions near carrots?
No, it’s a popular pairing. Onions and chives are often grown with carrots, since their scent may help mask carrots from carrot flies.
