Delphiniums are classic garden perennials admired for their magnificent, towering flower spikes, which bring a striking vertical element and vibrant color, most commonly in shades of blue, purple, and white. These plants are known to produce a spectacular first flush of blooms typically in early to mid-summer. Deadheading is the process of removing spent flowers from a plant. Proper care, including this targeted removal of faded blooms, helps ensure the continued vigor and display of the delphinium throughout the growing season.
Promoting Subsequent Flower Spikes
Deadheading is a direct intervention that manipulates the plant’s natural reproductive cycle to encourage further flowering. Once the primary flowers on the tall spike begin to fade, the delphinium shifts its biological resources toward the production of seeds (achenes). This reproductive process requires a significant investment of the plant’s energy, diverting it away from vegetative growth and flower production. Removing the spent flower spike before the seeds mature essentially tricks the plant into believing its initial reproductive effort has failed. This signals the delphinium to redirect the conserved energy and nutrients to new growth points. The plant responds by activating dormant buds located along the stem, resulting in the development of new, smaller lateral flower spikes. This energy redirection allows for a second, though often less dramatic, flush of color in the late summer or early fall, extending the overall ornamental value of the perennial.
Step-by-Step Guide to Making the Cut
The mechanical execution of the mid-season deadhead is precise and should be performed as soon as the main flower spike has finished blooming. Begin by using a pair of bypass pruners or sharp shears that have been cleaned to prevent the spread of disease. A clean cut minimizes damage to the remaining plant tissue, allowing it to heal quickly and focus energy on new growth.
Cutting Above a Lateral Shoot
Inspect the main, spent flower stalk and trace it down to where it meets the basal foliage or a strong, healthy lateral shoot. This lateral growth point, often marked by a small bud or a set of healthy leaves, is the location where the next flower spike will emerge. Make your cut just above this bud or leaf junction, ensuring you leave at least some of the stem and basal leaves to sustain the plant.
Cutting Back the Main Stalk
If the entire main stem has finished flowering and there are no strong side shoots visible, the correct technique is to cut the stalk back to just above the basal foliage near the crown of the plant. This cut should be made relatively low, about 6 to 12 inches above the soil line, depending on the plant’s size. Leaving the basal foliage intact is important because these leaves continue to photosynthesize, providing the energy needed for the secondary bloom.
End-of-Season Pruning
The final cut of the growing season is distinct from mid-season deadheading, as its purpose is to prepare the delphinium for winter dormancy. This pruning should be delayed until the foliage naturally begins to yellow and die back, typically occurring in late autumn after the first hard frost. Yellowing leaves indicate that the plant is withdrawing nutrients and energy back into its crown and root system for winter storage. Once the foliage has fully deteriorated, the entire plant should be cut back to a height of approximately six to eight inches above the soil line. Removing the dead and decaying plant material helps eliminate potential overwintering sites for pests and fungal diseases. Clearing this debris reduces the risk of moisture retention around the crown, which is a common cause of rot during the cold, wet months.