Basil is one of the most popular herbs and a staple of Italian cuisine. 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, as it turns out, is surprisingly particular about who or what it grows with. It belongs to 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 beds. 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 might first look. It releases oils through its leaves and roots that can either help or completely sabotage its neighboring plants.
These compounds – including eugenol, linalool and camphor – are what give basil its characteristic smell. But they also act as natural allelopathic agents in the soil.
On top of that basil is quite competitive for its resources. Despite being compact and smallish it develops a large root system that aggressively looks for nutrients and water.
The plant also has some certain needs that just don’t work with many common garden favorites. It needs warm soil, consistent moisture (but not waterlogged) and plenty 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 pair your Basil with the wrong plants it can result in:
- Stunted growth in both basil and the neighboring plants
- Reduced production of oils, making your basil less flavorful
- Increased susceptibility to pests and diseases
- Competition for nutrients leading to poor harvests
- 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 strong scents would be a great way to deter pests. What happened instead was I got to watch my beautiful basil plants slowly die off over the summer, producing fewer leaves and losing the lovely scent they’re known for.
Why it fails:
- Rue releases allelopathic compounds that will stop basil growing
- Both compete for similar nutrients but rue is more aggressive of the two
- The combined scents confuse insects you want to come to your garden
- Rue prefers drier conditions while basil needs consistent moisture
2. Cucumber
My stomach drove me on this one. It was the thought of fresh cucumber salads with my own homegrown basil. Yummy!
It wasn’t to be though. The cucumber plants near the basil patch struggled throughout the whole growing season and produced far fewer fruits than you would expect.
The problems:
- Basil can stop cucumber germination and early growth
- Both are heavy feeders and compete for the same nutrients
- The aromatic compounds from basil can stress cucumber plants
- Tricky to manage together as they have such different needs for water
3. Common Sage
Two herbs should get along, right? Wrong.
Trying sage and basil together was a total failure. They were both clearly very unhappy and produced poorly when compared to others that were planted on their own elsewhere.
Why they clash:
- Sage prefers dry, soil that drains well and basil needs consistent moisture
- The strong oils from both plants create chemicals that interfere with each other
- Different pH preferences – sage likes alkaline, basil prefers neutral
- Sage grows larger and can shade out basil plants
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, less flavorful leaves.
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
- Rosemary’s growth can crowd out basil
- Different soil pH requirements makes caring for grown both tricky
- Rosemary’s strong 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 deter lots of pests
- Parsley – Complement each other without competing
- Chives – Helps stop aphids and doesn’t have any impact on the basil’s growth
Tips for Successful Companion Planting
- Space appropriately – Even compatible plants 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 have similar needs. I’ve given my drought tolerant herbs their own area and they are much happier for it.
- Consider 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 per season now.
- Use succession planting – Plant new basil every 2 to 3 weeks so you get a continuous harvest without overwhelming any companion plants.
Final Thoughts
Basil isn’t as simple as I first thought it was. It needs the right companions to really thrive. The plants I’ve listed as poor companions aren’t necessarily bad plants – they just don’t fit well with what basil needs and it’s growing habits.
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 your climate. Plus the soil conditions can significantly impact plant relationships. Careful observation and willingness to make changes when plants aren’t thriving is going to be your greatest strength.
Keep detailed notes about what works and what doesn’t in your garden. My garden journal has saved me from repeating the same mistakes multiple times. Plus it’s helped me see successful combinations that aren’t mentioned in any gardening book.
The best companion planting advice comes from watching your own garden and learning what your plants are telling you.