When planning a thriving vegetable or herb garden, most people focus on sunlight, watering, and soil.
But one often-overlooked factor is plant compatibility. Just like people, plants have companions they get along with—and others they simply don’t.
Incompatible plants can stunt each other’s growth, attract unwanted pests, compete for nutrients, or even release chemicals into the soil that harm their neighbors.
That’s why understanding what not to plant together is just as important as knowing good companion plant pairings.
In this guide, we’ll explore 20 common plants and the ones they don’t grow well with, so you can plan a more harmonious, productive garden.
Why Some Plants Don’t Get Along
Before we get into the specific combinations to avoid, it helps to understand why plant incompatibility happens:
- Allelopathy: Some plants release chemicals that inhibit the growth of others.
- Nutrient competition: Plants with similar root depths or nutrient needs may compete.
- Pest attraction: One plant may attract pests or diseases that harm another.
- Shade interference: Tall plants can block sun from low-growing neighbors.
- Growth habits: Aggressive or spreading plants can crowd out others.
Now, let’s look at 20 popular vegetables and herbs and their incompatible plant partners.
1. Tomatoes
Avoid planting with:
- Corn: Attracts the same pests, including corn earworms and tomato fruitworms.
- Potatoes: Susceptible to similar diseases like blight; also compete for nutrients.
- Fennel: Inhibits tomato growth through allelopathy.
2. Potatoes
Avoid planting with:
- Tomatoes: Shared susceptibility to blight and pest problems.
- Cucumbers: Compete for the same nutrients and water.
- Pumpkins: Increase the risk of fungal diseases in both crops.
- Sunflowers: May stunt potato growth due to allelopathic compounds.
3. Carrots
Avoid planting with:
- Dill: Can stunt carrot root development as both are in the same family.
- Parsnips: Attract the same pests, including carrot root flies.
- Celery: Competes heavily for nutrients in the soil.
4. Cucumbers
Avoid planting with:
- Aromatic herbs like sage: May inhibit cucumber growth.
- Potatoes: Can lead to pest problems and poor root development.
- Melons: Compete for space, nutrients, and water.
5. Beans (Bush or Pole)
Avoid planting with:
- Onions: Inhibit bean growth and compete for nutrients.
- Garlic and leeks: Alliums in general stunt legume development.
- Fennel: Strongly allelopathic to beans and most garden vegetables.
6. Peppers
Avoid planting with:
- Fennel: Inhibits pepper plant growth.
- Kale and other brassicas: May cause competition and attract similar pests.
- Beans: Can inhibit each other’s growth depending on the variety.
7. Lettuce
Avoid planting with:
- Parsley: Can crowd out and stunt lettuce growth.
- Celery: May compete for similar shallow root space.
- Cabbage: The large leaves can overshadow and inhibit lettuce.
8. Corn
Avoid planting with:
- Tomatoes: Compete for nutrients and attract similar pests.
- Celery: May lead to cross-contamination of diseases.
- Brassicas: Prefer different soil pH and conditions.
9. Fennel
Avoid planting with: Almost everything.
Fennel is famously unfriendly in the garden. It releases chemicals that can inhibit or stunt the growth of nearly all vegetables and herbs. Plant it in its own bed, well away from other crops.
10. Garlic
Avoid planting with:
- Beans and peas: Garlic can inhibit nitrogen-fixing bacteria on legume roots.
- Strawberries: May hinder fruit development.
- Asparagus: Can slow growth and reduce yield.
11. Broccoli
Avoid planting with:
- Strawberries: Compete for nutrients and moisture.
- Tomatoes: Have different watering needs and may encourage pest problems.
- Pole beans: Can stunt growth when grown in close proximity.
12. Cabbage
Avoid planting with:
- Strawberries: Both suffer when planted together.
- Tomatoes and peppers: Compete for resources and are prone to similar pests.
- Pole beans: Growth habits conflict and may reduce yields.
13. Zucchini
Avoid planting with:
- Potatoes: Invite similar pests and fungal issues.
- Pumpkins: Compete for nutrients and space; cross-pollination is also possible.
- Cucumbers: Can increase the risk of powdery mildew.
14. Melons (Cantaloupe, Watermelon)
Avoid planting with:
- Cucumbers and squash: All attract cucumber beetles and powdery mildew.
- Potatoes: Can attract blight and compete for nutrients.
- Sage: May hinder melon development.
15. Onions
Avoid planting with:
- Beans and peas: Onions inhibit nitrogen-fixing activity.
- Sage: Both can suffer from reduced growth.
- Strawberries: Can interfere with fruit production.
16. Peas
Avoid planting with:
- Onions, garlic, leeks, shallots: All inhibit pea growth.
- Gladiolus (ornamental): Can stunt each other when grown together.
- Fennel: Poor companion due to its chemical properties.
17. Celery
Avoid planting with:
- Corn: Compete heavily for nutrients.
- Carrots and parsnips: Same root depth and resource needs.
- Turnips: May create excessive competition in limited space.
18. Strawberries
Avoid planting with:
- Cabbage family (broccoli, kale, cauliflower): Compete and may reduce berry yields.
- Tomatoes and eggplants: Can promote fungal diseases.
- Potatoes: May share similar pests, like rootworms.
19. Dill
Avoid planting with:
- Carrots: Similar structure can lead to cross-pollination and confusion.
- Tomatoes: Mature dill can stunt tomato growth.
- Peppers: May inhibit fruit production in some cases.
20. Sage
Avoid planting with:
- Cucumbers: The strong aroma of sage may deter cucumber growth.
- Rue: Another herb that reacts poorly when grown nearby.
- Onions and garlic: Can experience stunted growth.
How to Avoid Planting Incompatibilities
To keep your garden healthy and productive, follow these guidelines:
- Use a companion planting chart: Keep a printed or digital reference when planting.
- Practice crop rotation: Don’t plant the same family in the same spot year after year.
- Leave space between incompatible plants: If you must grow them, create distance.
- Group by plant families: Members of the same family often have similar needs (but beware of shared pests).
- Observe your garden: If a plant is underperforming, check nearby plant combinations.
Understanding incompatible plant pairings is essential for successful gardening.
While much attention is given to what plants grow well together, knowing what not to grow together can prevent disease outbreaks, pest problems, and poor yields.
By planning your garden with compatibility in mind, you can create a healthier, more productive growing environment—one that supports strong plants, better harvests, and fewer problems throughout the season.
