Cornflowers may be beautiful but they can be frustrating too. Plant them with the wrong plants or flowers and it can spell disaster.
I’ve seen firsthand what happens when cornflowers end up with bad neighbors. So I’ve got a list of plants that really don’t work together when it comes to planting companions for cornflower.
Understanding Cornflower
Cornflowers (also called bachelor’s buttons) give the appearance of being fragile and delicate. But their really pretty tough little flowers.
Last summer my cornflowers survived a three-week drought that killed half my garden. Which reminded me why I fell in love with these resilient flowers in the first place.
But while cornflowers aren’t high maintenance prima donnas, they definitely have preferences about their garden companions. Plant them with the wrong neighbors and you run the risk of stunted growth, fewer blooms or even total failure.
The main issues? Cornflowers need good airflow to prevent mildew problems, moderate soil moisture (not too wet), and they don’t play well with aggressive plants that’ll outcompete them for nutrients.
Getting it wrong can impact your entire garden plan. A friend of mine had to replant half her cutting garden because she didn’t realize her cornflowers were being suffocated by neighboring plants. So it pays to be careful with this.
Plants That Make Terrible Neighbors for Cornflower
1. Mint
I cannot stress this enough – never, ever plant mint anywhere near your cornflowers.
Mint’s aggressive root system will quickly overwhelm cornflowers (and pretty much everything else), stealing nutrients and water. Plus mint prefers more moisture than cornflowers do, creating competing needs that are impossible to satisfy.
If you absolutely must have mint in your garden keep it contained in pots far away from your cornflowers.
2. Tall Sunflowers
This pairing might seem tempting for a dramatic height contrast but tall sunflowers cast too much shade over cornflowers, which need full sun to thrive. I’ve seen sunflowers grow so tall and leafy that the neighboring cornflowers produced half as many blooms as those planted elsewhere.
What makes it problematic:
- Creates too much shade
- Sunflowers are heavy feeders that deplete soil nutrients
- The height difference makes watering difficult
- Can make cornflowers stretch awkwardly for light
3. Cucumbers and Squash
You’d think these vegetables would be innocent enough but their vining habits make them terrible cornflower neighbors. The cucumber vines will crawl over everything in sight, including your cornflowers. The leaves also create humid conditions that can lead to mildew problems for cornflowers.
4. Russian Sage
While both plants love sunny, dry conditions, Russian sage grows into a woody, large plant that will quickly outcompete cornflowers for space and nutrients. The sage’s size (it can reach 4 feet tall and wide) means it will overshadow your cornflowers, quite literally.
The problem:
- Too competitive for the same space
- Creates too much shade as it matures
- The deep roots of sage can interfere with cornflower’s more shallow root system
5. Coneflowers (Echinacea)
This one surprises many gardeners because both are wildflower meadow plants. But coneflowers grow much larger and spread more aggressively than cornflowers. I’ve seen cornflowers completely disappear within two seasons when planted alongside established coneflowers.
The issue isn’t just competition for space though. Coneflowers attract so many pollinators that your cornflowers might actually receive less attention from bees.
6. Strawberries
Strawberry plants might seem innocent but don’t be fooled. The way they spread and their moisture needs make them poor companions for cornflowers. The strawberry runners will quickly invade cornflower territory and strawberries’ preference for consistently moist soil goes against cornflowers’ more drought tolerant nature.
7. Tomatoes
I’ve tried planting cornflowers near tomato plants in the past. I thought their blue flowers would look great against the red fruits. Turned out to be a bit of a disaster. The tomatoes required much more water than the cornflowers and resulted in a watering conflict I couldn’t resolve.
Why they clash:
- Opposing water needs
- Tomatoes are susceptible to fungal issues that can spread
- Tomatoes need regular feeding, which can be too much for cornflowers
- Tomato cages and stakes can damage delicate cornflower stems
8. Hostas
The fact hostas love shade makes them fundamentally incompatible with cornflowers who love the sun. Either your hostas will suffer in the full sun that cornflowers need or your cornflowers will struggle in the shade that keeps hostas happy.
On top of that hostas prefer consistently moist soil while cornflowers perform best when the soil dries slightly between waterings. It’s an irreconcilable difference in your garden.
9. Aggressive Grasses (Like Mondo Grass)
Ornamental grasses might seem like natural companions for cornflowers but many aggressive varieties will quickly overwhelm them. The dense roots of grasses like mondo grass or ribbon grass compete directly with cornflowers for nutrients and water.
10. Butterfly Bush
While both attract pollinators butterfly bush grows too large and woody to be a good cornflower neighbor. Its size (reaching up to 10 feet tall) creates too much competition for light and nutrients.
What makes it problematic:
- Creates excessive shade
- Deep roots compete for water and nutrients
- The woody structure can physically damage cornflowers
- Can be too aggressive in many gardens
11. Cabbage Family Plants
Broccoli, cabbage and their relatives are heavy feeders that take a lot nitrogen from the soil – exactly what cornflowers need to thrive. Te frequent watering that cabbage family plants require also creates overly wet conditions for cornflowers.
I once planted cornflowers in a bed where cabbage had grown the previous season and they struggled all summer despite my best efforts. The soil was simply too depleted.
12. Fennel
Fennel is allelopathic. That means it releases chemicals that stop the growth of certain other plants. Unfortunately cornflowers are affected by these chemicals and will struggle when planted near fennel.
13. Morning Glory
Morning glory will use your cornflowers as living trellises if given half a chance. The weight of the vines can break cornflower stems and morning glories grow so rapidly that they can quickly overwhelm your blue blooms.
The worst part? Once established, morning glory can be nearly impossible to fully remove from your garden.
Good Companion Plants for Cornflower
So we’ve covered what not to plant. Let’s look at some fantastic cornflower companions:
- Cosmos – Similar growing conditions with complementary colors
- California Poppies – These orange beauties create stunning color contrast
- Calendula – Attracts beneficial insects and has similar needs
- Sweet Alyssum – Creates a fragrant carpet under taller cornflowers
- Zinnia – Similar growing conditions and bloom times
Tips for Successful Companion Planting
Spacing matters enormously – Give cornflowers at least 12 inches between plants. They need good air circulation to prevent mildew issues, especially in humid climates.
Consider mature sizes – That cute little plant might grow into a monster that overshadows your cornflowers. Always read those plant tags!
Match water needs – Cornflowers prefer soil that dries slightly between waterings. Pairing them with plants that need constant moisture creates an impossible situation.
Group by height – Plant taller companions to the north of cornflowers to avoid shading them out.
The year I finally got my companion planting right, my cornflowers produced nearly twice as many blooms as previous seasons. The right neighbors really do make all the difference.
Final Thoughts
Cornflowers may look like simple wildflowers but they have real preferences about their garden companions. Respect their need for sun, good drainage and breathing room and you shouldn’t have any problems.
The biggest lesson when it comes to companion planting? Plants are like people – they need compatible neighbors to thrive.
So before you place that cornflower next to an aggressive mint or sprawling cucumber, remember this guide. Your cornflowers will thank you and you’ll save yourself the frustration of watching them struggle unnecessarily.