Lobelia is one of those flowers that had me at hello. The first time I spotted those beautiful blue cascades tumbling from a hanging basket at my local nursery, I was smitten. So no surprise it’s become a staple in my garden design projects over the years.
But lobelia is not exactly the most sociable plant on the block. I once crammed it alongside some aggressive neighbors and watched my beautiful blue blooms struggle all season.
Understanding Lobelia
Regardless of whether you’re working with the upright varieties that stand proud in borders or the trailing types perfect for containers, knowing what NOT to plant with lobelia can save you a season of disappointment. Some plants will overshadow it, others compete too aggressively for nutrients & some just create conditions that lobelia absolutely hates.
I’ve killed enough lobelia plants to know that companion planting matters. Lobelia prefers cool, moist conditions with rich soil and it doesn’t appreciate being bullied by more aggressive plants. It’s a moderate feeder that won’t thrive if it has to fight for nutrients or moisture.
So before you plant your lobelia this season check out this list of plants that make terrible neighbors – trust me, your lobelia will thank you.
Plants to Keep Away From Your Lobelia
1. Marigolds
I love marigolds for their pest-repelling properties but they’re one of the worst neighbors for lobelia. Last spring I planted a beautiful arrangement with trailing lobelia and marigolds, thinking they’d complement each other visually. Big mistake.
Marigolds release substances from their roots that can inhibit the growth of certain plants, including lobelia. Marigolds also prefer hot, dry conditions while lobelia likes it cool and moist. Within weeks, my lobelia was looking stressed and producing fewer flowers.
2. Sunflowers
Talk about an uneven match! Sunflowers are the basketball players of the garden while lobelia is more like the gymnast. Not only do sunflowers create too much shade with their massive height but they’re also heavy feeders that will steal nutrients right out from under your lobelia.
I’ve seen sunflowers planted near a lobelia border – by midsummer, the lobelia was pale, straggly and barely flowering while the sunflowers thrived. The massive root systems of sunflowers can also physically crowd out the more delicate lobelia roots.
3. Mint and Other Aggressive Herbs
Never, ever plant mint anywhere near lobelia (or most other plants!) unless you want the mint to take over completely. I made this mistake in a container garden years ago and the mint literally choked out my lobelia within a month.
Mint, oregano and other spreading herbs have aggressive growth habits that will quickly overwhelm lobelia’s more genteel nature. They spread rapidly both above and below ground, and they don’t play fair when it comes to sharing resources. Keep them far away from your lobelia plantings.
4. Zinnias
Zinnias are sun worshippers that prefer drier conditions than lobelia. When I’ve tried this combination the result is always the same – either the zinnia suffers from too much moisture or the lobelia wilts from too much heat & dryness.
Also, zinnias tend to be susceptible to powdery mildew in humid conditions, which can spread to nearby plants. Since lobelia prefers those humid conditions this pairing often leads to disease issues for both plants.
5. Potentilla
The shrubby cinquefoil might seem like an innocent enough companion but its root system is more competitive than you’d think. When planted near lobelia, potentilla tends to dominate the soil resources.
I’ve observed this in several garden designs where the lobelia near potentilla shrubs was noticeably less vigorous than lobelia planted elsewhere. The difference was striking – about 40% less flowering in some cases.
6. Geraniums (Pelargoniums)
This might surprise you since geraniums and lobelia are often sold together in hanging baskets. The problem is they have conflicting needs. Geraniums prefer it hot and dry between waterings, while lobelia needs consistent moisture.
I’ve tried to make this classic combo work many times & it’s always a compromise – either the geraniums rot from too much water or the lobelia dries out and stops flowering. Commercial growers force them to work together with daily watering and heavy fertilization, but in a home garden, it’s a struggle.
7. Lavender
Lavender loves hot, dry and sunny conditions – basically the opposite of what lobelia wants. When I planted blue lobelia alongside lavender in what I thought would be a gorgeous purple-blue combo, the lobelia was crispy within weeks despite regular watering.
Lavender also prefers poor, sandy soil while lobelia wants rich, organic matter. Their fundamental needs are just too different to make good neighbors.
8. Yarrow
Yarrow is another drought-tolerant plant that creates conditions too dry for lobelia. Its extensive root system will also dominate and compete with lobelia for any available moisture.
9. Russian Sage
This popular perennial creates too much shade for low-growing lobelia and, like many drought-tolerant plants, creates soil conditions that are too dry. Its extensive root system also outcompetes smaller plants like lobelia.
Russian sage can reach 3-4 feet in height and spread, completely overshadowing small plants like lobelia. I’ve never seen this combination work well in any garden.
10. Black-Eyed Susan
These flowers might seem like good companions but black-eyed Susans are aggressive spreaders that will quickly crowd out lobelia. They also prefer drier conditions between waterings than lobelia can tolerate.
I once planted these together in a client’s “wildflower garden,” and by the second season there wasn’t a lobelia plant to be found – the black-eyed Susans had completely taken over.
11. Nepeta (Catmint)
Another case of conflicting water needs. Nepeta thrives in dry, sunny locations while lobelia wants consistent moisture. When planted together, one will always suffer.
The sprawling growth habit of nepeta also tends to smother smaller plants like lobelia. I’ve watched it happen in my own garden – the catmint just keeps expanding until it’s engulfed everything nearby.
12. Coreopsis
Coreopsis and lobelia have such different water requirements that they make for terrible neighbors. Coreopsis needs excellent drainage & dry conditions, while lobelia wants consistent moisture.
I’ve observed garden centers selling these together because their colors complement each other, but in practice, this is a combination headed for trouble.
13. Sedum
Any succulent, including sedum, creates soil conditions too dry for lobelia to thrive. Their water requirements are simply incompatible.
I tried this combination in a “waterwise” garden section once, thinking I could reduce water needs gradually. The lobelia lasted about two weeks before showing serious stress signs. Some plants just aren’t meant to be neighbors.
Plants That Love Lobelia
Now that we know what to avoid, what plants actually make good neighbors for lobelia? Here are a few companions that share similar growing conditions:
- Impatiens – They share lobelia’s love of consistent moisture and partial shade
- Fuchsia – Another shade-loving plant that enjoys the same conditions
- Begonias – Especially good with lobelia in containers
- Sweet Alyssum – Creates a beautiful carpet effect when planted with lobelia
- Bacopa – Similar trailing habit and water requirements
I’ve had particular success with the lobelia alyssum combo in hanging baskets. The white alyssum creates a beautiful contrast with blue lobelia & they both flower all season with similar care requirements.
Tips for Successful Companion Planting with Lobelia
These are my best tips for keeping lobelia happy:
- Always group plants with similar water needs – this is the number one rule
- Consider height and spread – don’t let other plants overshadow your lobelia
- In containers, place lobelia on the edges where it can trail freely
- Maintain rich, moist soil with plenty of organic matter
- In hot climates, provide afternoon shade to keep lobelia blooming longer
I’ve found that adding a slow-release fertilizer specifically formulated for flowering plants helps keep lobelia blooming throughout the season. Just be careful not to overdo it – too much nitrogen will give you lots of green growth but fewer flowers.
Final Thoughts
Lobelia might be a bit particular about its growing conditions and companions but it’s worth the effort to get it right. Those blue, purple or white flowers are simply stunning when the plant is happy.
After killing lots of Lobelia I learnt the lessons. Now I always make sure to plant it with compatible neighbors and the results speak for themselves – months of continuous blooms instead of weeks of struggle followed by decline.
The most important factor is matching water needs. Lobelia wants consistent moisture without being waterlogged, rich soil and protection from intense afternoon sun in hot climates. Give it these conditions and compatible neighbors and it will reward you with a season-long show of color.
So before you plant your lobelia this year take a moment to consider what’s going in next to it. Your garden’s beauty (and your wallet) will thank you for making smart companion planting choices from the start.