Delphiniums, often recognized by their common name, larkspur, are majestic herbaceous perennials prized for their tall, striking flower spikes. These towering columns of color are a signature element in many garden designs. However, they are not naturally continuous bloomers. The plant is a heavy feeder that expends a tremendous amount of energy on its primary display, and producing a second, smaller flush of flowers requires specific intervention and optimal growing conditions.
The Delphinium’s Natural Bloom Cycle
The life cycle of the delphinium prioritizes a single, massive reproductive effort in late spring and early summer. The main flowering period typically begins around June and lasts for several weeks, culminating in a spectacular, dense display of blooms. This initial flush is the plant’s biological peak, after which its focus naturally shifts away from flower production.
As the long, hollow flower spikes fade, the plant begins to invest its resources into developing seeds within the spent flower casings. This process signals the end of the primary blooming season, causing the plant to slow its vegetative growth significantly. Delphiniums thrive in moderate temperatures and do not tolerate intense summer heat and humidity well.
When high summer heat arrives, the plant may enter a period of stress or semi-dormancy, which halts any further development of new flower buds. Without intervention, the plant retains the spent flower stalks as it matures its seed, effectively concluding its floral contribution for the year.
Cultivating the Second Bloom
Coaxing a delphinium to produce a second, albeit smaller, flush of blooms requires cutting back. As soon as the majority of the flowers on the main spike have faded, the entire stalk must be removed to prevent the plant from diverting energy into seed development. This technique initiates a new reproductive cycle.
The spent flower spike should be cut down dramatically, generally to within a few inches of the ground, or just above the basal foliage that surrounds the plant’s crown. Leaving this healthy, low-lying foliage intact is important because it continues to photosynthesize, providing the energy needed for the new shoots to emerge. New, shorter flower spikes will begin to form from the base within a few weeks of the cutback.
To support this forced second effort, the plant requires an immediate nutritional boost following the cut. A dose of balanced liquid fertilizer, or one higher in phosphorus, replenishes the reserves depleted by the first bloom. This extra feeding provides the necessary fuel for the plant to generate new growth and develop the second set of flower buds, which typically appear in late summer or early autumn.
Essential Site and Soil Conditions
Delphiniums require a specific environment to support their energy-intensive growth and potential for reblooming. They perform best when situated in a location that receives full sun—a minimum of six hours daily—but with protection from the harsh, direct rays of the afternoon sun, especially in hot regions. A sheltered spot is also necessary, as the plant’s tall, hollow stems are highly susceptible to wind damage, which can prematurely end the first bloom.
The soil must be rich, loamy, and highly fertile to satisfy the plant’s appetite as a heavy feeder. Excellent drainage is absolutely necessary, as delphinium crowns are prone to rot in soggy conditions. Incorporating generous amounts of organic matter, such as compost or aged manure, before planting helps to maintain the slightly neutral to alkaline soil pH of 6.5 to 7.5 that the plant prefers.
Because of their impressive height and fragile stems, tall delphinium cultivars must be staked early in the season, often when they reach about a foot in height, to provide structural support. Maintaining good air circulation around the plants is important for preventing fungal issues like powdery mildew. Consistent watering, applied directly to the base of the plant, combined with well-drained soil and staking, creates the foundational health required for the two-stage bloom cycle.