Basil is one of the most popular herbs and a staple of Italian cooking. But when it comes to growing it you have to be careful what you plant alongside it.
I planted my first herb garden many years ago now. I thought basil would look nice next to pretty much everything so went a bit mad with it. Which was a silly mistake.
Basil is choosy about what it grows with. It part of the mint family and like its relatives it does not get along well with many other plants and flowers.
So I’m going to save you the hassle of finding out for yourself which plants don’t work. The following on this list should be avoided when it comes to planting your basil.
Understanding Basil
The first time I grew basil I treated it like any other herb and scattered it randomly throughout my garden. But pretty soon after I noticed some plants were doing well and others were struggling. It took me a full season to realize it was the basil that was reason why some weren’t growing.
Basil is more complex than you might first think. It releases oils through its leaves and roots that can either help or teapot affect its neighboring plants negatively.
These substancres are what give basil its characteristic smell. But they also act as have allelopathic effects on other plants, which stops them growing.
On top of that basil is fights for its resources. Despite being fairly small it develops big roots that aggressively looks for nutrients and water.
It also needs things that just don’t work with many common garden favorites. It needs warm soil, consistent moisture (but not getting waterlogged) and a lot of sunlight. If you try planting it with plants that have different needs they both end up suffering.
Why Getting Basil Companions Wrong Matters
If you get it wrong and plant your Basil with the wrong plants it can result in:
- Poor growth in both basil and the neighboring plants
- Reduced production of oils, making your basil have much less flavor
- Increasing likely to be affected by pests and diseases
- Fighting for nutrients which results in a poor harvest
- Wasted garden space and disappointing yields
So definitely something you want to avoid.
Plants NOT to Grow With Basil
1. Rue
I planted rue and basil together thinking their scents would be a great way to keep away pests. But instead all I got to do was watch my beautiful basil plants slowly die away over the summer, with fewer and fewer leaves and losing the scent they’re known for.
Why it fails:
- Rue releases allelopathic substances that will stop basil growing
- Both fight for the same nutrients but rue is more aggressive of the two
- The two scents confuse insects you want to come to your garden
- Rue likes drier conditions while basil needs consistent moisture
2. Cucumber
The thought of fresh cucumber salads with my own homegrown basil was too much for me to resist.
It didnt work out though. The cucumber plants near the basil struggled throughout the whole growing season and produced far fewer fruits than you would expect.
The problems:
- Basil can stop cucumbers from germinating and early growth
- Both take up a lot of fight for the same nutrients
- The aromatic substances from basil can stress cucumber plants
- Its tough to manage together as they have such different needs for water
3. Common Sage
Two herbs should get along fine. Or so I thought. Planting sage and basil together was a total failure.
They were both clearly very unhappy and grow poorly when compared to others that were planted on their own elsewhere.
Why they clash:
- Sage likes dry soil that drains well and basil needs lots of moisture
- The strong oils from both plants create chemicals that mess up each how each other grow
- Different pH preferences – sage likes alkaline, basil likes neutral
- Sage grows big and can stop the sun getting to the basil
4. Fennel
Fennel is notorious for being a difficult neighbor with everything. Basil is no exception.
I should have known better but gave it a try anyway. I hoped they’d both attract beneficial insects but neither plant did well and it just didn’t work.
What goes wrong:
- Fennel releases compounds that inhibit most other plants, including basil
- Both have large root systems that compete hard against one another
- The anise scent of fennel will overpower basils scent
- Can be awkward to manage them both as they have different times for harvesting
5. Thyme
Another herb combination that on the gave of it seems logical but works terribly. My thyme and basil border was a disappointment with the thyme eventually dominating. The basil produced smaller leaves that has much less flavor.
The issue:
- Thyme prefers much drier conditions than basil
- The way likes to spread can crowd out basil
- Different soil preferences make giving them both the right care pretty much impossible
- Thyme’s stems crows out the more gender growth of basil
6. Black Walnut Trees
Walnut trees simply don’t like anything. Try planting virtually any plant with them and it’s doomed to failure.
Basil will be no exception and even I’d you give it the best care it’ll die.
Why it’s problematic:
- Black walnut produces juglone which is toxic to basil and so many other plants
- The allelopathic effect extend way beyond the tree’s canopy
- Even fallen leaves and nuts will release the damaging compounds
- No amount of care can get around this
7. Mint
You’d think family members would get along but mint and basil very much don’t. Even though they are both part of the Lamiaceae family they can’t grow together without their being issues.
What happens:
- Mint’s is super aggressive spreading and will quickly overwhelm basil
- As the mint grows and takes over the roots complete heavily
- Mint can cross pollinate with Basil which affects it’s flavor
- Both release similar but competing aromatic compounds
8. Rosemary
I thought that rosemary and basil would complement each other well. Them both being Mediterranean herbs.
But the basil never grew particular well and produce fewer leaves as well as losing most of its intense flavor.
The problems:
- Rosemary needs very dry conditions while basil likes consistent moisture
- How rosemary grows can crowd out basil
- Different soil pH requirements makes caring for grown both tricky
- Rosemary’s scent can mask and hide the delicate basil
9. Oregano
Another herb family member that competes rather than complements. Grown together they do much less well than when grown apart.
Why it doesn’t work:
- Both compete for the exact same nutrients and growing conditions
- Oregano’s spreading habit can overtake basil plantings
- Similar but competing scents confuse insects that would help out your garden
- As they can cross contaminate it can affect the quality of both of them
10. Beans
My rows of beans did not like it when I planted basil near them. In my head the Basil was going to keep pests away. What actually happened was the beans gave me much less pods than when they were left alone.
What goes wrong:
- Beans need nitrogen and basil interferes with them getting it
- When the roots compete with one another it affects how well the beans develop
- Basil’s aromatic compounds can stress bean plants
- Managing them both when they are harvested at different times is difficult
11. Sunflowers
The height difference alone makes this pairing not work. But there are bigger issues too.
The issue:
- Sunflowers create too much shade for basil that loves and needs the sun
- Both are heavy feeders and will compete hard for nutrients
- Sunflowers can release allelopathic compounds
- The height difference makes proper care of both plants difficult
12. Carrots
This pairing seemed promising since both like loose soil that drains well. But when I tired it the results were disappointing. A lot of the carrots were stunted or misshapen.
Why they clash:
- Basil’s scent can stop the carrot seeds from germinating
- Root competition affects how well the carrots develop
- Challenging to care for them well when they have such different water needs
- Harvesting one affects the roots of the other
13. Brussels Sprouts
I thought basil might help keep pests away from my Brussels sprouts. But if anything this seemed to attract more problems than it solved. Both plants looked stressed all the time.
The problems:
- Brussels sprouts are heavy feeders that compete with basil
- The large leaves of Brussels sprouts stop the sun from getting to the basil
- As they need different nutrients from the soil they both end up deficient in some areas
- Increased humidity between plants can make fungal diseases more likely
Good Plants to Grow With Basil
So after lots that don’t work I’m happy to say that basil does have some plants that work with it.
- Tomatoes – The classic pairing that actually works! Basil improves the flavor of tomatoes and helps keep pests away
- Peppers – Both love warm conditions and the basil helps stop aphids and spider mites
- Eggplant – Similar growing requirements with basil helps keep flea beetles from becoming a problem
- Marigolds – Adds some lovely color and works with the basil to keep away lots of pests
- Parsley – Look good together without fighting
- Chives – Helps stop aphids and doesn’t have any impact on how the basil grows
Tips for Successful Companion Planting
- Space appropriately – Even plants that work well together need a good amount of space. I give basil at least 12 inches from most of the neighboring plants and up to 18 inches from larger plants.
- Group by water needs – Basil does best with consistent moisture so I group it with plants that like the same. I’ve given my herbs that don’t need a lot of water their own area and they are much happier for it.
- Think about harvest timing – Plant basil with companions that won’t be disturbed by the need to harvest them often. Annual herbs and vegetables work better than perennial plants.
- Monitor soil conditions – Use a simple soil test kit to make sure the pH and nutrients work for all plants in the area. I test my basil beds twice every season now.
- Use succession planting – Plant new basil every 2 to 3 weeks so you get a continuous harvest without it taking over any companion plants.
Final Thoughts
Basil isn’t as simple as I first thought it was. It needs the right companions to really do well.
The plants I’ve listed as poor companions aren’t necessarily bad plants – they just don’t fit well with what basil needs and how it grows.
Success comes from understanding what each plant’s requires rather than making assumptions based on how they look or family relationships.
But what works in a Zone 7 garden will likely need some tweaking in yours. Plus the soil conditions can have a big impact on how plants work together. Careful observation and be able to make changes when plants aren’t thriving is going to be your greatest strength.
You can keep notes about what works and what doesn’t in your garden. My garden journal has saved me from repeating the same mistakes more than once. Plus it’s helped me see successful combinations that aren’t mentioned in any gardening book.