13 Plants to Avoid Planting With Tomatoes This Season

Tomatoes are one of the most common vegetables for home gardeners to grow. There are many different types of tomatoes and while most can grow just fine by themselves in the garden, many tomatoes do much better when planted with a different type of neighboring plant. This process is known as companion planting.

Tomatoes have many great companions in the garden that can help with pollination, fruit production, and even taste. But with the good also comes the bad.

Several types of plants should never be planted near your tomatoes. Planting with poor companion plants will increase the risk of pest infestation, diseases, and nutrient competition. Let’s take a deeper look at the plants you should try to avoid planting near your tomatoes this season.

How Companion Planting Works

Also known as intercropping or interplanting, companion planting partners plants together that will have beneficial effects on one another.

Historically, companion planting was based mostly on folklore and trial and error, with little knowledge of which plants are scientifically compatible or incompatible. There is a lot to be said about simply knowing what works and what doesn’t based on observation.

However, we now have scientific resources to turn to, and relevant information about how and why specific plants affect one another, which saves a lot of time.

Ideally, companion planting provides benefits for both, or all plants involved. Plants that are mutually beneficial to each other are the best companions, although there are occasions when an ornamental plant can be placed with edibles to no benefit of its own, except that it increases pollination for the edibles.

The video below explains a bit more about the science behind companion plants.

Now that you have a better understanding of how companion planting works and the science behind it, let’s take a look at some of the plants you should avoid planting near your tomatoes!

Broccoli

This pairing has a greater negative impact on broccoli than on your tomatoes, but it’s still good to know if you plan to plant both of these veggies.

Broccoli and tomatoes are both heavy feeders, and while tomatoes might come out on top in this competition, it will be better for both, in the long run, to keep them separated.

Brassicas (of which broccoli is a member) and nightshades (tomato fits into this group) typically do not thrive together. They both require a lot of nutrients and will compete, leaving one or both crops looking and tasting subpar. For best results, give these two vegetables at least 3 feet of space from one another.

If you want to make it easy on yourself, pick an entirely different plant to pair with broccoli in the garden.

Brussels Sprouts

Brussels sprouts are brassicas as well, so they are not compatible with tomatoes. Tomatoes will suffer from this union with stunted growth as brussels sprouts hog all of the nitrogen in the soil leaving tomatoes to languish on their leftovers.

To give tomatoes the best chance, keep these two vegetables in separate beds. Both need full sun, plenty of water, and nitrogen-heavy fertilizer.

Cabbage

Cabbage is another member of the brassica family of vegetables, which means they don’t mix with tomatoes and will inhibit the tomatoes’ growth. Cabbage and tomatoes together mean small fruits and reduced yield.

Cabbages also need a lot of nutrients. They are heavy feeders, and so are tomatoes. In this relationship, the tomatoes rarely win the battle over nutrients. These two simply do not mix. Cabbage has a long list of friendly companions, so you are better off choosing another plant.

Cauliflower

Tomatoes and cauliflower do not make good neighbors as well, and for the same reason. Cauliflower is a brassica, and they will compete for nutrients, leaving both vegetables with lackluster production.

It might be tempting to see if cauliflower helps hold in the moisture to protect tomato roots, but the reality is that neither plant will benefit from this union.

Better to pair either plant with beans! Beans help make nitrogen in the soil more available to other plants and have a vining habit, making this pair a good space saver.

Corn

Tomatoes and corn are poor companions because they share a very destructive, common pest. Heliothus zea is the larvae of the corn earworm, a moth that goes by the scientific name Helicoverpa zea.

This worm goes by another common name, Tomato Fruitworm. This pest specifically attacks the fruit of the plant and will render every fruit they touch inedible.

Because these plants share a common pest that is known to be highly destructive, it is best to plant them apart. Once the pests move in, they will have no reason to leave if there is plenty of food for their offspring and could end up decimating both crops.

Dill

Most herbs grow very well with tomatoes, but dill is an odd plant out in that category. When dill is young, it can have beneficial effects on tomatoes. For instance, aphids find dill to be a repellent, and this pairing would benefit tomatoes in that way.

Sadly, the pairing would not remain beneficial in the long term. Once dill blooms, it ceases to be a good neighbor for tomatoes. When dill goes to seed, it will rob the soil of nutrients that tomatoes need, stunting their growth and quality of fruit.

Eggplant

Eggplants and tomatoes should technically work well together, as they are both nightshades and have similar needs. However, they will compete for nutrients, and tomatoes might not come out on top.

In addition, tomatoes grow much taller than eggplants, and eggplants don’t like to be kept in the shade.

Eggplants are particularly vulnerable to blight, which places their neighbors in a risky situation. Having these plants close to your tomatoes will increase the tomato plant’s vulnerability to blight as well. It’s best to keep these two apart.

Because they compete for nutrients, stick with other eggplant companions when planning out your garden.

Fennel

Fennel is an interesting plant — and more often than not, you will find it on a list like this! In most cases, they portray fennel as a horrible companion.

Reasons often given are that it causes other plants to bolt, ruins their flavor, inhibits their growth, or even kills plants altogether by secreting a chemical from its roots that can cause other plants – a form of allelopathy.

The irony is that fennel is also an incredible plant to stop tomato fruitworm and tomato hornworm, as it often draws in beneficial insects that directly attack these larvae. Tachinid flies/wasps are often brought in by its flowers, in particular, and these can be an incredible boon in the garden! It’s also a larval plant for butterflies and a generally great pollinator plant.

Is it actually allelopathic? Well… yes and no. Yes, it is allelopathic, although most often, that’s towards certain kinds of flowers or competitive weeds. Most established tomatoes don’t have a problem with them, and many of the other concerns only apply to leaf lettuces or other green leafy plants.

But if you are concerned and have heard horror stories about planting fennel in your garden, you may want to plant them in a nearby container or grow bag instead.

Hot Peppers

Hot peppers and tomatoes may work well together in salsa, but when it comes to garden beds, they should be kept apart. Both are vulnerable to blight, which can build up in the soil, so keeping these out of each other’s space is a good idea, long-term.

These plants also share a common garden pest. The tomato hornworm (Manduca quinquemaculata) is fond of the foliage of both plants, so placing them together means that both crops are affected if these guys show up.

This doesn’t mean peppers can’t be good companions in the garden. There are just other plants that pair better with peppers in your garden beds.

Kale

Typically, kale and nightshades make good companions. Kale and eggplant are friends, and peppers work well with kale, also. Tomatoes, however, tend to grow quite large and so they use up a lot of nutrients. This causes kale to suffer.

This is not a hard and fast rule. The two can grow together if they have the right nutrient supply. If you decide to plant kale with your tomatoes, make sure to give them plenty of nitrogen-rich fertilizer.

As with other plants on this list, kale has plenty of different plants that make far better companions in the garden.

Kohlrabi

Because kohlrabi is a brassica, it immediately becomes another bad tomato neighbor. If you recall, these plants will compete with tomato plants for nutrients, especially nitrogen.

These plants need at least 3 feet of distance from each other in the garden and would be better served by planting in separate beds altogether.

Potatoes

Because potatoes are nightshades, they will compete with tomatoes for nutrients. These two plants will be vulnerable to the same diseases, which means that when one is infected, you are likely to lose both.

Another complication of potatoes as companions comes at harvest time. Digging up potatoes can cause harm to tomato roots. Overall, this is not a good match.

Potatoes have many other companions that will not only benefit their growth but can subjectively enhance their taste.

However, one exception to this rule is the “Ketchup And Fries” grafted plant. This is an unusual tomato in that it’s only a tomato on top – it’s grafted onto a potato plant.

This Frankenstein-like plant can’t have both crops harvested at once, however; you’ll have to wait until after you’ve canned your tomatoes and they’ve died back to harvest your spuds.

Walnuts

Walnuts, particularly black walnut trees, are often cautioned against by gardeners, and there’s a good reason: juglone. The black walnut tree secretes this naturally-occurring chemical through its roots primarily, although it’s also found in the walnut hulls and, to a lesser extent, in the leaves.

Most of this occurs in the soil around the tree’s root zone, and as you might guess, a healthy black walnut has a pretty sizeable root zone. Juglone is an allelopathic compound, meaning it can prohibit plant germination or cause damage to some young plants it makes contact with. (But not all plants – some don’t even notice it!)

Some solanaceous plants are extremely sensitive to the juglone secreted by the tree, so it’s recommended not to plant tomatoes directly underneath a black walnut.

If you have nowhere else to plant other than directly under the walnut tree, use a raised bed and pick out any hulls or leaves that drop into your bed. However, tomatoes like full sun, so planting them directly under a tree may not be your best bet!

Juglone does not persist in the soil. It has a relatively short half-life in the soil and any hulls, leaves, or chipped wood. If the plant materials are finely chipped, hot-composted, and then aged for up to six months before use, there will be no more juglone in the remaining composted material, and it’ll be safe for garden use.

But if you don’t have a reliable hot composting system, it’s probably best to keep your tomatoes away from both the compost and the tree.

Final Thoughts

Companion planting can increase your harvest, enhance soil quality, and improve the flavor of your edible plants. Tomatoes benefit from many pairings, and in particular, tons of herbs make wonderful companions for tomatoes. Happy planting!