What NOT to Plant with Tomatoes (Avoid These Common Mistakes!)

This post may contain affiliate links.

Tomatoes are one of the most rewarding vegetables to grow, but even the healthiest plants can struggle if they’re growing next to the wrong neighbors.

While companion planting can improve growth and reduce pests, some plants compete for nutrients, attract the same insects, or increase the risk of disease.

If you want bigger harvests and healthier tomato plants, avoid planting these vegetables and herbs nearby.

Why Companion Planting Matters

Choosing the right companions helps tomatoes by:

Improving airflow
Reducing pest problems
Encouraging pollinators
Maximizing garden space
Reducing the spread of disease

Just as important is knowing which plants don’t make good neighbors.

Want to try making your own jelly at home?

Get my free guide with 8 easy, beginner-friendly jelly recipes you can confidently make.

1. Corn

Although tomatoes and corn seem like natural garden companions, they share one major problem—they attract many of the same pests.

Both plants are susceptible to tomato fruitworms (also called corn earworms), making it easier for infestations to spread throughout your garden.

Plant instead: Basil, marigolds, or carrots.

2. Fennel

Fennel is one of the few vegetables that doesn’t play well with almost anything.

It releases compounds into the soil that can slow the growth of nearby plants, including tomatoes.

For the healthiest garden, grow fennel in its own bed or container.

3. Potatoes

Tomatoes and potatoes belong to the nightshade family, which means they share many of the same diseases and pests.

Growing them together increases the chances of problems like:

Early blight
Late blight
Colorado potato beetles
Aphids

Planting them in separate areas helps reduce disease spread.

4. Eggplant

Eggplant is another member of the nightshade family.

Because it attracts many of the same insects and diseases as tomatoes, planting them side by side can make pest management much more difficult.

5. Peppers

Although peppers and tomatoes are often used together in the kitchen, they aren’t always ideal garden companions.

Both crops:

Require similar nutrients
Attract aphids and other pests
Can spread diseases between plants

If space allows, separate them by a few garden beds.

6. Cabbage and Other Brassicas

Cabbage, broccoli, cauliflower, Brussels sprouts, kale, and other brassicas can compete heavily with tomatoes for nutrients.

These crops also prefer cooler growing conditions, while tomatoes thrive in warm summer weather.

Keeping them separated allows both crops to perform better.

7. Walnut Trees

If you’ve ever wondered why nothing grows beneath walnut trees, the answer is juglone.

Black walnut trees produce this natural chemical, which is toxic to tomatoes and many other vegetables.

Never plant tomatoes beneath or near black walnut trees.

8. Rosemary, Sage, and Other Woody Herbs

While basil is one of the best tomato companions, woody Mediterranean herbs like rosemary and sage have different watering needs.

These herbs prefer drier soil, while tomatoes need consistent moisture for healthy fruit production.

Growing them separately usually leads to healthier plants.

The Best Companion Plants for Tomatoes

Instead of the plants above, consider growing these tomato-friendly companions:

Basil

One of the most popular tomato companions.

Many gardeners believe basil helps repel insects while improving tomato flavor.

Marigolds

Marigolds attract beneficial insects and may help reduce certain soil pests.

Their bright flowers also attract pollinators.

Garlic

Garlic can help deter aphids and other common garden pests while taking up very little space.

Onions

Onions make excellent companions because they don’t compete heavily for nutrients and may discourage some insects.

Carrots

Carrots grow below the soil while tomatoes grow above it, making efficient use of garden space.

Lettuce

Lettuce enjoys the afternoon shade created by tomato plants and helps maximize your harvest in small gardens.

Spinach

Spinach grows quickly in spring before tomatoes reach full size, making it an excellent companion crop.

Nasturtiums

These colorful flowers attract pollinators while acting as a trap crop for aphids and other insects.

Frequently Asked Questions

Can tomatoes and peppers grow together?

Yes, they can, but it’s generally better to separate them if possible since they share many of the same pests and diseases.

Can tomatoes and cucumbers be planted together?

Yes. Tomatoes and cucumbers can grow together successfully if given enough spacing for good airflow.

What is the best companion plant for tomatoes?

Basil, marigolds, garlic, onions, carrots, lettuce, spinach, and nasturtiums are all excellent companion plants for tomatoes.

Related Companion Planting Guides

If you’re planning your vegetable garden, you may also enjoy:

Growing tomatoes isn’t just about sunlight and fertilizer—it’s also about choosing the right neighbors.

By keeping corn, potatoes, fennel, brassicas, and other incompatible plants away from your tomatoes, you’ll reduce pest problems, lower disease pressure, and give your plants the best chance to produce an abundant harvest.

Pair your tomatoes with beneficial companions like basil, marigolds, garlic, and carrots, and you’ll be well on your way to healthier plants and bigger harvests all season long.

Follow my gardening board on Pinterest.