I’ve seen plenty of carnation catastrophes over the years. I remember Elaine from my garden club who planted her prized carnations right next to her mint – within weeks her carnations were struggling while the mint thrived. These mishaps happen more often than you’d think.
I’m going to share what I’ve learned about planting carnations – both the flowers that make terrible neighbors and the ones that actually help your carnations thrive.
Understanding Carnations
Carnations (Dianthus caryophyllus) aren’t just the cheap filler flowers you see at supermarkets. When grown properly they produce gorgeous, fragrant blooms that can transform any garden space. I’ve grown everything from the classic pink varieties to the more unusual green carnations & they never fail to impress visitors.
But there’s no denying they can be somewhat particular about their growing conditions. They prefer well-drained, slightly alkaline soil with a pH between 6.7 and 7.5. They’re also sun-lovers that need at least 4-5 hours of direct sunlight daily to produce the blooms we all love.
But here’s where things get tricky – carnations don’t play nice with every plant. Some neighboring plants will compete aggressively for nutrients, some create shade problems and others can increase disease risks. Getting these combinations wrong isn’t just disappointing – it can be downright disastrous for your carefully nurtured carnations.
Last spring I made the rookie mistake of planting some carnations too close to my vegetable garden. The tomatoes grew faster than expected, casting afternoon shade over my carnations. The result? Leggy stems, fewer blooms, and ultimately, a disappointing display that had me kicking myself all season.
Plants That Should Never Share Space With Carnations
1. Mint and Other Aggressive Herbs
Mint might smell amazing but it’s the neighborhood bully of the garden world. Its aggressive spreading habit means it will quickly invade the root space of your carnations, stealing water and nutrients while physically crowding them out.
Why they’re incompatible:
- Mint’s invasive root system will quickly overcome carnation roots
- Mint will steal water and nutrients
- Once established, mint is extremely difficult to fully remove
2. Tall Sunflowers
Sunflowers make stunning vertical statements in the garden but they’re terrible companions for carnations. The height difference isn’t just an aesthetic issue – it’s a practical problem too.
Carnations need those 4-5 hours of direct sunlight I mentioned earlier, and tall plants like sunflowers will rob them of that essential light.
Why they’re incompatible:
- Sunflowers cast significant shade
- They can grow 6-10 feet tall, completely overwhelming carnations
- Sunflowers are heavy feeders that will compete for nutrients
- Their large root systems can physically crowd carnation roots
3. Potatoes and Other Solanaceae Family Members
Tomatoes, potatoes, peppers & eggplants all belong to the nightshade family and they bring trouble to carnations. These plants are susceptible to similar fungal diseases that can spread to your carnations.
Why they’re incompatible:
- Share common fungal diseases that can easily spread
- Compete for similar nutrients
- Different watering needs create problems
4. Black Walnut Trees
If you have black walnut trees anywhere near your property, be very careful about planting carnations. Or, frankly, anything! These trees produce a chemical called juglone that’s toxic to many plants, including carnations.
Why they’re incompatible:
- Juglone toxicity can stunt or kill carnations
- Effect radius extends well beyond the tree’s canopy
- Toxin remains in soil even after tree removal
5. Climbing Vines and Sprawling Plants
Morning glories, clematis and other climbing or sprawling plants may seem like good vertical companions but they’ll quickly overtake your carnations.
I once thought it would look charming to have some sweet peas growing up trellises behind my carnation bed. Within weeks the sweet peas had sent tendrils into the carnation foliage, tangling & pulling down stems as they sought support.
Why they’re incompatible:
- Physical entanglement damages carnation stems
- Vines can block critical airflow, increasing disease risk
- Competition for light and nutrients
6. Tropicals and High-Water Plants
Carnations prefer moderately dry conditions between waterings. Tropical plants and water-lovers like elephant ears, cannas or astilbe have completely different moisture needs.
Last season I tried interplanting some carnations with Japanese iris in a bed that stayed fairly moist. The iris thrived but the carnations developed root rot before June was over. Lesson learned – keep these plants in separate beds with appropriate watering regimes.
Why they’re incompatible:
- Different watering needs – carnations hate wet feet
- Increased humidity around carnations promotes fungal problems
- Competing root systems with different requirements
7. Eucalyptus and Strong-Scented Plants
You might think fragrant plants would complement carnations but strong-scented plants like eucalyptus, camphor and some artemisias release aromatic compounds that can actually inhibit the growth of neighboring plants.
I noticed this effect when I planted wormwood near my carnations as a pest deterrent. The carnations closest to the artemisia grew noticeably smaller and produced fewer blooms than those further away.
Why they’re incompatible:
- Allelopathic compounds can stunt carnation growth
- Conflicting fragrances may affect pollinator behavior
- Many aromatic plants prefer drier conditions than carnations
8. Aggressive Self-Seeders
Plants that aggressively self-seed can quickly overtake a carnation bed. Before you know it your carnations are fighting for space with hundreds of seedlings.
Why they’re incompatible:
- Seedlings can quickly overwhelm carnation beds
- Removal without damaging carnations is difficult
- Competition for light, water, and nutrients
9. Plants That Attract Harmful Pests
Some plants act as magnets for pests that will then move on to your carnations. I’ve found that members of the cabbage family (kale, broccoli etc.) attract aphids that eventually find their way to carnations.
Why they’re incompatible:
- Increased pest pressure on carnations
- May require more pesticide use
- Can weaken plants making them susceptible to disease
10. Dense Ground Covers
Ground covers like creeping jenny or ajuga might seem like good options for covering soil around carnations but they can choke out carnation seedlings and compete with established plants.
Why they’re incompatible:
- Physical crowding of carnation stems
- Competition for soil resources
- Can increase humidity around stem bases
Good Companion Plants for Carnations
Now that we know what to avoid let’s quickly go over what actually works well with carnations. I’ve had great success pairing my carnations with:
- Lavender – similar water needs and the slight shade can be beneficial
- Dianthus (other varieties) – family members usually play well together
- Salvia – upright growth habit complements carnations
- Yarrow – drought-tolerant and attracts beneficial insects
- Geraniums – similar growing conditions and complementary colors
These plants not only look good with carnations but they actually help them thrive by either deterring pests or attracting pollinators.
Tips for Successful Companion Planting with Carnations
These are my top tips for successfully growing carnations with companion plants:
- Always research mature sizes – that cute little plant in the nursery might become a monster!
- Consider the vertical space – plant taller companions to the north of carnations
- Group plants with similar watering needs
- Leave enough space between plants for airflow to prevent fungal diseases
- Watch for signs of competition – yellowing leaves, reduced flowering, or stunted growth
Final Thoughts
Growling plants is always about experimentation. What works in a Zone 6b garden (or wherever it might be garden) might need adjustments in your growing conditions. Keep notes, take plenty of pictures and don’t be afraid to move plants that aren’t thriving together.
The joy of gardening comes from these constant adjustments and the knowledge that next year will always be better.