Companion planting is a well-known gardening technique that helps plants thrive by placing compatible species together.
However, some plants should never be grown next to each other due to competition for resources, pest attraction, or chemical interference.
Growing incompatible plants side-by-side can stunt growth, reduce yields, or even kill certain crops.
To ensure a productive and healthy garden, avoid planting these 14 incompatible plant pairings together.
1. Tomatoes & Potatoes
Why They Don’t Work Together:
Both tomatoes and potatoes are susceptible to blight, a devastating fungal disease that spreads quickly. If one plant becomes infected, the disease can easily wipe out both crops.
Better Companions:
- Plant tomatoes with basil to improve flavor and repel pests.
- Grow potatoes near beans to enhance nitrogen levels in the soil.
2. Onions & Beans
Why They Don’t Work Together:
Onions release sulfur compounds that can inhibit bean growth. Beans, in turn, require nitrogen-rich soil, which onions do not provide.
Better Companions:
- Grow onions near carrots or lettuce to deter pests.
- Pair beans with corn or squash for natural support and nutrient sharing.
3. Cucumbers & Aromatic Herbs
Why They Don’t Work Together:
Cucumbers need a moist environment, whereas aromatic herbs like basil, rosemary, and sage prefer drier soil. The strong scent of these herbs can also affect cucumber pollination.
Better Companions:
- Grow cucumbers with radishes to repel cucumber beetles.
- Pair herbs with tomatoes to enhance growth and pest resistance.
4. Carrots & Dill
Why They Don’t Work Together:
Dill can stunt carrot growth by releasing chemicals that interfere with root development. Additionally, dill attracts carrot-loving pests like carrot flies.
Better Companions:
- Grow carrots with onions to deter pests naturally.
- Pair dill with cabbage or broccoli for improved health.
5. Peppers & Fennel
Why They Don’t Work Together:
Fennel releases compounds that inhibit the growth of many plants, including peppers. It can also attract pests that feed on nightshades.
Better Companions:
- Grow peppers with basil to improve flavor and repel insects.
- Keep fennel separate or near dill for pollinator attraction.
6. Lettuce & Broccoli
Why They Don’t Work Together:
Broccoli is a heavy feeder that absorbs nutrients quickly, leaving little for lettuce, which needs consistent soil fertility.
Better Companions:
- Grow lettuce with radishes for shade protection.
- Plant broccoli near beets to reduce nutrient competition.
7. Corn & Tomatoes
Why They Don’t Work Together:
Both corn and tomatoes attract the corn earworm and tomato hornworm, which can devastate both crops when grown together.
Better Companions:
- Grow corn with beans for nitrogen enrichment.
- Pair tomatoes with marigolds to repel pests.
8. Cabbage & Strawberries
Why They Don’t Work Together:
Cabbage and strawberries attract the same pests, including cabbage worms and aphids, increasing the risk of infestation.
Better Companions:
- Grow cabbage with thyme to deter pests.
- Pair strawberries with garlic for natural pest control.
9. Sunflowers & Potatoes
Why They Don’t Work Together:
Sunflowers produce allelopathic chemicals that can hinder potato growth and reduce yield.
Better Companions:
- Grow sunflowers near beans to attract pollinators.
- Pair potatoes with horseradish to deter diseases.
10. Basil & Rue
Why They Don’t Work Together:
Rue releases chemicals that can stunt basil growth and inhibit its essential oil production.
Better Companions:
- Grow basil with tomatoes for pest control and flavor enhancement.
- Pair rue with roses to deter Japanese beetles.
11. Beans & Peppers
Why They Don’t Work Together:
Beans are nitrogen fixers, while peppers prefer low nitrogen levels. This imbalance can lead to excessive foliage growth in peppers, reducing fruit production.
Better Companions:
- Grow beans with corn for natural support.
- Pair peppers with parsley for improved growth.
12. Radishes & Hyssop
Why They Don’t Work Together:
Hyssop can stunt radish growth and reduce yield.
Better Companions:
- Grow radishes with cucumbers to repel pests.
- Pair hyssop with grapes for a beneficial relationship.
13. Spinach & Grapes
Why They Don’t Work Together:
Grapes cast too much shade, which can prevent spinach from getting the sunlight it needs.
Better Companions:
- Grow spinach with strawberries to improve ground cover.
- Pair grapes with garlic to repel pests.
14. Cauliflower & Tomatoes
Why They Don’t Work Together:
Tomatoes and cauliflower both compete heavily for nutrients, leading to stunted growth.
Better Companions:
- Grow cauliflower with celery for enhanced pest resistance.
- Pair tomatoes with marigolds to keep pests away.
Knowing which plants to keep apart in your garden is just as important as knowing which ones to plant together.
By avoiding these 14 bad companion pairings, you’ll improve plant health, maximize yields, and create a thriving, pest-resistant garden.
