Have you noticed that azaleas struggle to grow under a black walnut tree? Or that beans planted near sunflowers never flourish? Those are two examples of combative plants. If you’re interested in companion planting, it’s time to brush up on which plants don’t get along.
The problem with some incompatible plants like black walnut is their negative allelopathy. It’s where a plant produces chemicals that adversely affect the germination and growth of those around them. Others like corn and tomatoes compete intensely for the same resources.
Just like picking places for your guests at a formal dinner party, it’s important to know which plants to separate.
We selected twenty combative vegetables and other incompatible plants to give you a head start on planning your garden. Group the right vegetables, and you’ll have a bountiful harvest.
Black Walnut – A Very Combative Plant
Black walnut trees are a well-know combative plant. Every part of the tree contains juglone, a chemical that cripples plants like hydrangeas, azaleas, lilies, petunias, blackberries, tomatoes, eggplant, and corn.
If you have a black walnut tree near your garden, keep in mind that the tree roots could spread underneath the soil and wreak havoc. Plants that tolerate black walnut trees include some flowering trees, tulips, violets, black-eyed Susan, daffodils, honeysuckle, and a few other trees like box elders.
If you chop down a black walnut tree, the roots may still be a problem. If the tree roots have impeded your sewer lines you can make a do-it-yourself sewer root killer to eliminate the issue.
Broccoli thrives in moist soil between sage, oregano, rosemary, and peppermint. It likes artichokes as long as the artichoke leaves don’t shade it. But it’s not a fan of basil.
And it can cause problems for tomatoes, strawberries, peas, and some kinds of beans. Broccoli needs to be rotated to a new site each year. Otherwise, it builds up toxins in the soil.
Brussels sprouts are good companion plants for the majority of garden vegetables except for strawberries, tomatoes, and pole beans. The list of friendly neighbors includes celery, beets, cucumbers, onions, dill, turnips, garlic, sage, rosemary, potatoes, spinach, and Swiss chard.
Nasturtiums and marigolds repel squash bugs that afflict Brussels sprouts. At the same time, mustard is a sacrificial plant that protects the shoots by attracting pests away from them.
When you plant seeds, put cabbage near herbs like garlic, dill, mint, thyme, and rosemary. These herbs keep pests like loopers and diamondback moth larvae away from the cabbage. Chard, celery, and spinach make excellent companions, too.
Moreover, both cabbage and spinach perform better in cool weather. Happily, cabbage and potatoes go well together just like they do in soup. But keep strawberries, tomatoes, basil, and pole beans far from cabbage in the garden.
Carrots – Among the Most Combative Plants in Your Garden
Carrots don’t get along with celery, parsley, dill, or anise and are combative vegetables. This may seem odd since we often cook these together in delicious dishes. But the sage and rosemary are helpful because they repel rust flies.
Companion plants for carrots include beans, peas, lettuce, parsley, onions, and radishes. Legumes like beans, peanuts, and clover add nitrogen to the soil which helps carrots grow bigger. Also, chives improve the flavor of carrots and keep aphids away.
The cruciferous vegetable cauliflower, just like cabbage, doesn’t get along with basil. But it loves other herbs like mint and thyme as well as onions and garlic.
These strong aromas keep pests at bay. Plus, celery nearby repels cabbage worms. But remember to keep tomatoes and strawberries far away.
Corn is Combative with Tomatoes
Corn, beans, and squash are friends. Gardeners call them the “Three Sisters.” Corn also plays well with pumpkin, cucumber, melon, and potatoes.
Place soybeans nearby, they keep away chinch bugs from the corn. But tomatoes and corn will fight each other for resources like water and nitrogen. They also share pests in common like the corn earworm.
As much as you may enjoy flavoring cucumbers with aromatic herbs, these are incompatible plants that don’t grow well together. Keep cucumbers away from basil, rosemary, marjoram, and sage as well as late potatoes. The herbs will alter the flavor of the cucumber.
On the other hand, plant cucumber and dill together to attract beneficial insects. Or place cucumbers beside peas, beans, cabbages, and radishes.
The radishes repel cucumber beetles. Finally, don’t worry about artichokes shading cucumbers because the cucumbers can climb up towards the sun.
Fennel prefers to grow by itself. It irritates almost every plant in the garden except for dill. But dill and fennel cross-pollinate, which creates muddled results with altered flavors.
For best results, raise fennel in a container garden. Still, fennel does repel aphids and draws in ladybugs and other beneficial predators.
Garlic Hinders Beans’ Growth Potential
Garlic stinks, and it keeps pests away from tomatoes, cabbages, radishes, and roses. Planting garlic too close to peas and beans does not permit plants to reach their full potential.
Also, garlic and asparagus do not mix. Instead, locate garlic near fruit trees and roses.
Kale is part of the cabbage family. This means that it grows poorly next to tomatoes, basil, and strawberries. But if you raise kale next to onions, garlic, dill, and aromatic herbs like mint, it flourishes.
The strong-scented neighbors keep pests away without changing kale’s flavor. Additionally, kale grows well in shade and flourishes next to nasturtiums and marigolds. Nasturtiums are a trap plant that lures bugs like aphids away from other crops.
Lettuce is part of the daisy family that likes the company of cauliflower, beets, parsnips, and kale. But if you have garlic and onions on one side of your kale, put lettuce on the other side.
That’s because lettuce doesn’t get along with members of the Allium family including chives and shallots. It also tends to soften up summer radishes.
We just mentioned the Allium family which is comprised of onions, garlic, and chives. Odiferous onions do well with carrots, beets, and cabbages nearby.
But they’re incompatible with asparagus, peas, and beans. On the other hand, onions are excellent for repelling everything from small pests like maggots up to deer.
Peppers are members of the nightshade family which includes tomatoes, potatoes, eggplant, and tobacco. Unlike their relatives, peppers are more resistant to diseases and pests.
Just don’t plant sweet peppers next to fennel or kohlrabi, and keep a wide gap between hot peppers and beans or cabbage.
Pole beans grow vines while bush beans resemble shrubs. They fix nitrogen in the soil, which is a bonus for other plants nearby.
But don’t plant them near beets, cabbage, garlic, cauliflower, broccoli, chives, or onions. Instead, place bush beans between cabbage, carrots, cauliflower, cucumber, potatoes, corn, and spinach.
Then locate pole beans near potatoes, radishes, corn, and marigolds. For extra protection, place summer savory by pole beans to avoid Mexican beetles or learn how to use neem oil to repel them.
Potatoes – Don’t Plant Near Cucumbers!
Potatoes are relatives of eggplant, tomatoes, and peppers. On the downside, they’re prone to many of the same diseases and pests.
Moreover, they don’t grow well near tomatoes, radishes, pumpkins, spinach, cucumbers, or sunflowers. The same goes for cherries, apples, raspberries, and birch trees.
But they thrive near beans, corn, peas, squash, eggplant, and cabbages. Additionally, locate potatoes near marigolds, basil, and catnip to keep potato beetles and other harmful bugs away.
We slipped in a surprise. Spinach isn’t actually combative. It gets along with just about every plant in the garden. It’s especially compatible with cabbage, cauliflower, celery, eggplant, onions, peas, and strawberries.
This relative of Swiss chard and beets grows fast in cool weather like spring and fall. This means you can achieve two harvests per year while maintaining a demilitarized zone between combative plants.
Just remember it needs full sun and about a foot of space to spread.
Strawberries will suffer near cabbage or any of the cabbage family including broccoli and kale because those plants attract pests. Put bush beans, thyme, and sage near strawberries for better results. The herbs will protect them. Strawberries also like spinach, borage, and lettuce.
We’ve mentioned tomatoes several times already because they are hostile to several other plants like cabbage, cauliflower, and corn. But if you place tomatoes near basil, chives, and garlic, you’ll protect them from nematodes and hornworms.
They are also friends with asparagus, mustard, parsley, onions, rosemary, sage, and even stinging nettles.
Sunflowers are excellent for weed abatement. But be careful planting them near pole beans and potatoes.
Sunflower seeds contain toxins that slow down the growth of those plants. On the other hand, if you place cucumbers near sunflowers, the flowers shelter the vegetables and provide them with a natural trellis for their vines.
To sum up, it’s time to decide what you’ll grow this year and where you’ll plant it. To get you started, here are a few ideas. Grab your graph paper and a pencil to sketch out your thoughts.
At one end of your garden, start with sunflowers, cucumbers, and dill. Nearby, you can place radishes and cabbages because cabbage does well with dill, too. Dill also lures beneficial insects.
Then next to the cabbage, raise spinach, the friendly vegetable. Spinach is a convenient buffer plant that helps keep combative plants separate.
Think of it as a game and you might come to love companion planting. By thinking ahead, you’ll prepare for a delightful harvest.
If you found this article helpful, please share it. We enjoy creating new content to support gardening enthusiasts around the world.