12 Plants NOT to Plant with Delphiniums

Gardeners have long appreciated the towering beauty and vibrant colors of delphiniums, a favorite choice for borders and cottage gardens. These showy perennials, with their tall spikes and rich blues, purples, and whites, can create a stunning display. However, companion planting delphiniums requires careful consideration. Some plants can compete for nutrients, provide too much or too little shade, or simply do not thrive in the same conditions as delphiniums. Here, we explore twelve plants that you might want to reconsider when planning your garden ensemble with delphiniums.

Understanding Delphiniums

Before diving into the specific plants to avoid, it’s important to understand the needs and characteristics of delphiniums. They thrive in full sun to partial shade, preferring rich, well-drained soil with plenty of organic matter. Delphiniums also need ample water, especially during dry spells, but must not sit in soggy soil, which can lead to root rot. They are hardy in USDA zones 3 to 7 and can benefit from staking due to their tall growth habit.

The Importance of Companion Planting

Companion planting is a time-tested technique for improving garden success, promoting biodiversity, and encouraging beneficial insects while keeping pests at bay. Some plants thrive synergistically when planted together, while others may hinder their growth or health. Here is a list of twelve plants that may not make ideal companions for delphiniums.

1. Sunflowers (Helianthus spp.)

Sunflowers are eye-catching and easy-to-grow annuals that many gardeners use as a backdrop for shorter plants. However, sunflowers can overshadow delphiniums due to their height and broad leaves. They require full sun, which can leave delphiniums in too much shade if planted too closely. Sunflowers also deplete the soil of nutrients quickly, creating competition that delphiniums struggle to win.

2. Echinacea (Echinacea purpurea)

While both echinacea and delphiniums thrive under similar sunlight conditions, echinacea prefers a slightly more arid environment. Its drought-resistant nature means it does not require as much water as delphiniums, which can lead to an imbalance in your watering practices if planted together. This can make it challenging to give each plant what it needs to thrive.

3. Roses (Rosa spp.)

Roses are beloved for their blossoms and scent, but they demand a lot of attention and resources, such as nutrients and water, which delphiniums also need. Additionally, both plants are prone to fungal diseases like powdery mildew, and planting them together can exacerbate the spread of these diseases.

4. Hostas (Hosta spp.)

Hostas are popular for their lush foliage and shade tolerance. However, their love of shade means they aren’t compatible with sun-loving delphiniums. Furthermore, hostas can create too much shade if planted nearby and thrive in the moist soil conditions that may lead to the decline of delphiniums due to excessive water.

5. Mint (Mentha spp.)

Mint is well-known for its vigorous growing habit and tendency to overtake garden beds, potentially choking out other plants, including delphiniums. Its extensive root system and ability to spread rapidly make it a less than ideal companion for almost any plant, but especially for those like delphiniums that have a more delicate root system.

6. Lamb’s Ear (Stachys byzantina)

Lamb’s ear is prized for its silvery foliage and drought tolerance. Unfortunately, its preference for dry soil conditions clashes with the delphinium’s need for consistent moisture. Additionally, lamb’s ear can spread densely, leading to competition for space and nutrients.

7. Liatris (Liatris spicata)

Known for its striking vertical flower spikes, liatris prefers dry, sandy soils and full sun. While it shares the preference for sun with delphiniums, liatris does not fare well in the rich, moist soil conditions that delphiniums require. This difference in soil preference can make it difficult for both to coexist happily.

8. Lavender (Lavandula spp.)

Lavender’s Mediterranean origins make it suited to dry, well-draining, and sunny conditions. Although lavender and delphiniums both enjoy full sun, lavender’s need for dry soil makes it challenging to share garden space with moisture-loving delphiniums. Overwatering lavender to meet the needs of delphiniums can lead to root rot in the lavender.

9. Dahlias (Dahlia spp.)

Dahlias are renowned for their showy blooms, yet they are heavy feeders and compete intensely for nutrients. Both dahlias and delphiniums are demanding in terms of soil richness and fertility, so they may find themselves in a tug-of-war for the same resources. Moreover, dahlias’ dense foliage can overshadow the base of delphiniums, impeding their growth.

10. Sedum (Sedum spp.)

Sedum, or stonecrop, is ideal for rockeries and dry areas. It prefers well-draining soil and minimal watering, making it incompatible with moisture-loving delphiniums. Sedum’s low-growing, spreading habit also poses a risk of encroachment into the space needed by delphinium’s deep roots.

11. Yucca (Yucca spp.)

Yucca plants bring an architectural flair to gardens with their spiky leaves and tall flower stalks. Nevertheless, yuccas thrive in poor, dry soil, in stark contrast to the nutrient-rich environment delphiniums demand. Their substantial root systems also leave little room for delphiniums to spread their roots effectively.

12. Camellias (Camellia spp.)

Camellias are cherished for their winter and spring blooming, but they prefer acidic, well-draining soil, whereas delphiniums thrive in a more neutral to alkaline environment. The differing pH needs and camellias’ tendency toward shade don’t align well with the conditions that maximize delphinium growth.

Conclusion: Thoughtful Pairings for Garden Harmony

While delphiniums are undeniably captivating, they benefit greatly from thoughtful pairing with garden companions that enhance their best traits without adding undue competition or adverse conditions. By avoiding the twelve plants mentioned above, you can help ensure your delphiniums thrive, bringing their majestic spikes and vibrant colors to your garden.

For improved success with companion planting, consider pairing delphiniums with plants such as Shasta daisies, foxglove, or peonies, all of which share similar growing conditions and complement delphiniums both visually and ecologically. By choosing compatible companions, you can cultivate a harmonious and thriving garden space that showcases the beauty of your beloved delphiniums.