Bad Companion Plants For Basil

Growing basil is one of the great joys of gardening. Its fragrant leaves bring so much flavor to the kitchen. But did you know some plants can actually harm your basil’s growth? Knowing the bad companion plants for basil is key to a healthy, productive herb garden. Avoid planting near these species to ensure your basil thrives.

Companion planting is the practice of placing certain plants together for mutual benefit. It can improve pest control, enhance flavor, and boost growth. However, some plants compete for resources or attract harmful insects. Getting your plant pairings wrong can lead to weak, stunted basil. Let’s look at which neighbors to keep far away from your basil patch.

This list includes plants that directly compete with or harm basil. Keeping these out of your basil’s immediate vicinity is a good first step to success.

Rue: This herb is perhaps the worst companion for basil. Gardeners have long observed that rue can stunt basil’s growth. The reasons aren’t fully understood, but they seem to chemically inhibit each other. It’s best to plant them in completely different garden beds.
Sage: While both are herbs, sage and basil are not good friends. Sage prefers dry, less fertile soil and too much water can cause it to rot. Basil, on the other hand, needs consistently moist, rich soil. Their conflicting needs mean one will always suffer if planted together.
Thyme: Similar to sage, thyme is a Mediterranean herb that loves dry conditions. Planting it next to thirsty basil creates an imbalance. The frequent watering basil requires can lead to root rot in thyme. Their growth habits also differ greatly, with thyme being a low creeper and basil an upright annual.
Common Mint: Mint is a notoriously aggressive spreader. Its vigorous roots will quickly overtake the space, choking out nearby basil. Mint also prefers a bit more shade and moisture than basil ideally likes. If you must grow mint, always plant it in a separate container, never directly in the ground near your herbs.
Fennel: Fennel is allelopathic, meaning it releases substances into the soil that inhibit the growth of other plants. It’s a bad companion for almost everything, especially basil. Fennel will severely stunt your basil’s development and should be grown in its own isolated spot.

Why These Plants Cause Problems

The issues usually come down to three main factors: water needs, soil nutrition, and chemical interactions. Basil is a heavy feeder that likes moist soil. Herbs like sage and thyme thrive in poorer, drier dirt. When you try to meet one’s needs, you hurt the other.

Some plants, like rue and fennel, release compounds from their roots or leaves. These compounds can supress the germination or growth of sensitive plants like basil. It’s a natural form of competition, but it’s bad news for your pesto plans.

Vegetables to Be Cautious Of

It’s not just herbs that can cause trouble. A few common vegetables are also poor companions for basil due to competition or pest sharing.

Cucumbers: This is a tricky one. Some gardeners report success, but many find basil and cucumbers compete for water. Cucumbers are heavy drinkers with large vines that can shade out smaller basil plants. If you try it, ensure both have ample space and consistent watering.
Potatoes: Potatoes and other tubers require hilling of soil around their stems. This disturbs the shallow roots of basil plants. They also attract similar pests that can easily jump between them.

A Note on Brassicas

Plants like cabbage, kale, and broccoli (the brassica family) have mixed reviews. Basil can help repel some pests that bother them, like aphids. However, brassicas are also heavy feeders. They may out-compete basil for nutrients if the soil isn’t ammended regularly. If you plant them together, monitor your basil’s growth closely.

What About Flowers?

Most flowers are excellent companions for basil. They attract pollinators and beneficial insects. However, avoid strong-smelling flowers like marigolds planted right next to basil. Some gardeners believe the very potent scent can alter the delicate flavor of the basil leaves. Planting them a few feet away is a safer bet.

Great Companion Plants For Basil

Now that we know what to avoid, let’s focus on the good neighbors. These plants will help your basil flourish.

Tomatoes: This is the classic companion pairing. Basil is said to improve the flavor of tomatoes and repel pests like thrips and flies. They enjoy similar soil and watering conditions, making them perfect garden partners.
Peppers & Eggplant: As fellow members of the nightshade family, they share basil’s love for warm weather and consistent moisture. Basil can help deter aphids, spider mites, and other common pests from these plants.
Oregano & Parsley: Unlike its Mediterranean cousins, these herbs make good companions. They have similiar water and soil needs and create a beneficial ground cover that helps retain soil moisture.
Lettuce & Spinach: Basil can provide light, dappled shade for these cool-weather greens, extending their growing season. The basil benefits from having its soil kept cool and moist by the leafy greens.
Beans & Asparagus: Basil helps repel the asparagus beetle and the bean beetle. Planting basil nearby can lead to a healthier crop of these vegetables.

How to Plan Your Garden Layout

Keeping the bad companions away is easier with a simple plan. Follow these steps.

Sketch Your Beds: Draw a simple map of your garden space. Mark areas of full sun (6-8 hours), which basil requires.
Group by Need: Create a “Mediterranean Herb” zone for thyme, sage, and rosemary in drier, sunnier spots. Create a “Moisture-Loving Herb” zone for basil, parsley, and cilantro in richer, well-watered soil.
Use Containers: For aggressive or allelopathic plants like mint and fennel, use dedicated pots. This physically prevents them from interfering with your in-ground plants.
Consider Succession Planting: If space is limited, you can plant a bad companion after your basil is finished. For example, you could plant sage in the fall where summer basil was, once you’ve harvested the basil completely.

Signs Your Basil is Struggling From Bad Companions

How do you know if your basil is suffering from a poor neighbor? Look for these clues.

Stunted Growth: The plant remains small and doesn’t bush out, despite good weather.
Yellowing Leaves: This can indicate nutrient competition or improper watering for its needs.
Wilting: Consistent wilting, even when watered, can mean root competition or chemical inhibition.
Poor Flavor: Leaves may taste weak or off if the plant is stressed or competing with strong-smelling plants.

If you see these signs, check what’s planted within a 12-18 inch radius. You may need to carefully transplant either the basil or its troublesome neighbor.

FAQ: Basil Companion Planting

Can I plant basil next to rosemary?

It’s not recommended. Rosemary, like sage and thyme, prefers dry, sandy soil. Basil’s need for frequent watering will likely cause the rosemary to develop root rot. They are better off in separate garden sections.

What should you not plant next to basil?

The main plants to avoid are rue, sage, thyme, common mint, and fennel. Be cautious with cucumbers and potatoes, too. Their care requirements or growth habits often clash with basil’s needs.

Does basil need to be planted in pairs?

No, basil does not need to be planted in pairs. It grows perfectly well as a single plant. However, planting multiple basil plants together can create a nice, full patch and improve your overall harvest. Just give each plant enough space, about 6-12 inches apart.

Where is the best place to plant basil?

Plant basil in a location that gets full morning sun (at least 6-8 hours daily). The soil should be well-draining but rich in organic matter. Keep it consistently moist but not soggy. A spot near tomatoes, peppers, or parsley is ideal for companion benefits.

Can basil and cilantro be planted together?

Yes, basil and cilantro can be planted together. They have similar water and soil needs. Cilantro grows quickly in cooler weather, while basil takes off in the heat. They often complement each other’s timing in the garden bed.

By understanding which plants are bad companion plants for basil, you set your garden up for success. Avoid planting near the problematic species we’ve discussed. Instead, focus on grouping basil with its friends like tomatoes and peppers. With a little planning, you’ll have a bountiful harvest of fragrant, healthy basil all season long. Remember, observation is your best tool—watch how your plants interact and don’t be afraid to adjust your layout next year.