What Should Not Be Planted Next to Tomatoes: A Guide to Companion Planting Mistakes to Avoid

What Should Not Be Planted Next to Tomatoes: A Guide to Companion Planting Mistakes to Avoid

Tomatoes are a backyard garden staple for many American families. Their delicious, sun-ripened flavor is hard to beat. But like any good relationship, a tomato plant benefits from good neighbors and suffers from bad ones. Planting the wrong vegetables or herbs too close to your precious tomato vines can lead to a host of problems, from stunted growth and disease to pest infestations and reduced yields. Understanding what *not* to plant next to tomatoes is just as crucial as knowing what *to* plant for a thriving garden.

The Worst Neighbors for Your Tomatoes

Some plants are natural enemies of tomatoes, actively competing for nutrients, harboring diseases that affect tomatoes, or even attracting pests that have a taste for your prized fruit. Here's a breakdown of the common culprits you should keep your tomato plants well away from:

1. Brassicas (Cabbage Family)

This includes a wide variety of popular garden vegetables:

• Broccoli
• Cabbage
• Cauliflower
• Kale
• Brussels Sprouts
• Kohlrabi

Why they are bad neighbors: Brassicas are known as "heavy feeders," meaning they are very demanding on soil nutrients. They will aggressively compete with tomatoes for essential elements like nitrogen, phosphorus, and potassium, leading to weakened tomato plants that are more susceptible to diseases and produce fewer fruits.

2. Corn

While corn and tomatoes might seem like classic summer crops, they are not good garden companions.

Why it is a bad neighbor: Corn is a heavy feeder and is particularly susceptible to the same pests that can plague tomatoes, such as the corn earworm and the tomato hornworm. Planting them together can create a breeding ground and an easy buffet for these damaging insects, essentially doubling your pest problems.

3. Potatoes

Despite both being nightshades and growing underground, potatoes and tomatoes are not friends in the garden.

Why they are bad neighbors: Both tomatoes and potatoes belong to the Solanaceae family, also known as the nightshade family. This shared family ties them to common diseases, most notably early blight and late blight. If one plant gets infected, the disease can easily spread to the other, decimating your crop.

4. Fennel

This aromatic herb, while popular in some cuisines, is a definite no-go for tomato companions.

Why it is a bad neighbor: Fennel is known to inhibit the growth of many other plants, including tomatoes. It is believed to release certain compounds into the soil that are detrimental to tomato development. It's best to keep fennel in its own separate garden area.

5. Walnuts (Black Walnut Trees)

If you have a black walnut tree in your yard, you'll need to be strategic about where you plant your tomatoes.

Why they are bad neighbors: Black walnut trees release a chemical called juglone into the soil. Juglone is toxic to many plants, including tomatoes, and can cause wilting, yellowing of leaves, and eventual death. Tomatoes are particularly sensitive to juglone, so avoid planting them anywhere within the drip line of a black walnut tree.

6. Cruciferous Vegetables (similar to Brassicas but worth a specific mention for some gardeners)

While covered under Brassicas, some gardeners might specifically group things like:

• Radishes
• Mustard Greens

Why they are bad neighbors: Similar to other Brassicas, these can compete for nutrients and may not create an ideal soil environment for tomatoes.

7. Dill

While dill is an herb, and many herbs are good for tomatoes, dill is an exception.

Why it is a bad neighbor: Dill can attract spider mites, which can then spread to your tomato plants. Furthermore, mature dill can stunt tomato growth. It's generally recommended to plant dill away from tomatoes, or to harvest it before it matures and potentially poses a problem.

The Underlying Principles of Bad Companionship

Understanding *why* certain plants are bad neighbors helps you make informed decisions for your entire garden:

• Nutrient Competition: Some plants are simply more aggressive in their nutrient uptake. If they are planted too close, your tomatoes will be starved.
• Disease and Pest Transmission: Plants in the same family are more likely to share and spread diseases. Likewise, some plants attract pests that also target tomatoes.
• Growth Inhibition: Certain plants release compounds into the soil that can actively hinder the growth of others.

What to Plant Instead: Good Tomato Companions

While it's important to know what to avoid, knowing what *to* plant is equally beneficial. Excellent companions for tomatoes include:

• Basil: Repels flies and mosquitoes, and is believed to improve tomato flavor.
• Carrots: Loosen the soil and don't compete for the same resources.
• Onions and Garlic: Repel pests like aphids and spider mites.
• Marigolds: Deter nematodes and other soil-borne pests.
• Borage: Attracts beneficial pollinators and is thought to improve tomato flavor and growth.

FAQ Section

How far away should I plant tomatoes from corn?

To avoid pest issues and nutrient competition, it’s best to plant corn at least 10 to 20 feet away from your tomato plants. This provides a good buffer zone.

Why shouldn't I plant potatoes next to tomatoes?

Tomatoes and potatoes are both part of the nightshade family (Solanaceae). This means they share susceptibility to the same devastating diseases like early blight and late blight. Planting them together makes it very easy for these diseases to spread from one plant to the other, potentially destroying your entire crop.

Can I plant fennel near my tomatoes?

No, it's strongly advised against planting fennel near tomatoes. Fennel is known to inhibit the growth of many other plants, and tomatoes are particularly sensitive to its effects. Keep your fennel in a separate part of the garden.

How does black walnut affect tomatoes?

Black walnut trees produce a toxic chemical called juglone. This chemical leaches into the soil and is harmful to many plants, including tomatoes. Tomato plants are highly sensitive to juglone and can suffer from wilting, yellowing, and even death if planted too close to a black walnut tree.

What is the main reason to avoid planting brassicas next to tomatoes?

The primary reason to avoid planting brassicas (like broccoli, cabbage, and kale) next to tomatoes is nutrient competition. Brassicas are very heavy feeders and will deplete the soil of essential nutrients that tomatoes need to thrive, leading to weakened plants and reduced yields.