Delphinium plants are admired for their striking, towering spires of flowers, which bring a distinctive vertical element to garden beds. Whether these plants return each year depends heavily on the specific variety and the quality of care provided. Most popular, large-flowered varieties are classified as perennials, meaning they possess the potential to regrow annually from the same root crown. However, their successful return is not guaranteed and requires diligent attention, especially during winter dormancy.
Understanding Perennial and Annual Varieties
The confusion surrounding the return of these plants stems from the existence of both perennial and annual types, often grouped under the common name “larkspur.” Stately garden varieties, such as the Delphinium elatum hybrids, are true perennials capable of living for multiple seasons. These perennial types are characterized by thick, dense flower spikes and deeply lobed foliage.
Conversely, annual larkspur, or rocket larkspur, belongs to a different genus, Consolida (Consolida ajacis or Consolida ambigua), and completes its entire life cycle in a single growing season. While annual larkspur may appear to return due to prolific self-seeding, the original plant never regrows. Gardeners seeking the reliable return of a mature clump must ensure they plant the perennial Delphinium species.
Year-Round Maintenance for Vigor
A strong summer growing season is necessary for the plant to build the reserves required to survive winter dormancy. Delphiniums thrive in rich, organically enhanced, and well-draining soil with a neutral to slightly alkaline pH. They require six to eight hours of full sunlight daily, though they appreciate afternoon shade in regions with intense summer heat.
The tall, hollow flower stems necessitate mechanical support to prevent breakage in wind or heavy rain. Staking should be done early in the season, typically when the plant reaches about 12 inches in height, to secure the developing stalk. As heavy feeders, these plants benefit from consistent moisture and the application of a balanced fertilizer every few weeks starting in early spring.
After the initial bloom period fades, cutting back the spent flower spike, known as deadheading, is important for plant health. This action diverts the plant’s energy away from seed production and can encourage a second, smaller flush of blooms in late summer or early autumn. The spent stalk should be cut down to a small, side-flowering shoot, preserving foliage to continue generating energy.
Critical Steps for Winter Dormancy
Proper preparation for cold weather is the primary factor determining if a perennial delphinium will return in the spring. Once the foliage has begun to yellow and die back, typically after the first hard frost, the stems should be cut down. Shear the remaining stalks to a height of about six to eight inches above the ground.
The most significant threat to the plant’s survival over winter is crown rot, caused by excessive moisture pooling around the dormant crown. Excellent drainage is necessary, and any debris or old foliage around the base of the plant must be removed to improve air circulation. A winter mulch, such as pine needles or straw, should be applied after the ground has frozen solid to maintain a consistent soil temperature.
This layer of mulch, typically two to three inches deep, prevents the shallow root system from being damaged by freeze-thaw cycles that can heave the crown out of the soil. Keep the mulch material pulled slightly away from the immediate crown area to prevent persistent dampness and fungal issues. As temperatures warm in early spring, the winter mulch should be gradually pulled back to allow new growth to emerge.
Why Healthy Delphiniums Still Fail to Reappear
Even with careful cultural practices, perennial delphiniums can occasionally fail to return due to external pressures or internal limitations. The delicate, new spring shoots are a prime target for slugs and snails, which can quickly decimate the emerging growth right at the soil line. Inspecting the crown for signs of these pests as the weather warms can protect the new buds.
Disease is another major cause of failure, with crown and root rot being the most common. This fungal issue often manifests as wilting or blackening near the soil line and is nearly always a result of poor drainage or overwatering. Powdery mildew, while rarely fatal, can severely weaken the plant by inhibiting photosynthesis, making it less likely to generate the energy needed for subsequent years.
Finally, the inherent nature of the perennial varieties contributes to their eventual disappearance, as they are considered short-lived. Most hybrid delphiniums only persist for an average of two to five years before their central crown becomes woody and loses vigor. To maintain a continuous presence, gardeners must periodically divide the mature clumps every few years to rejuvenate the plant.