Delphiniums, with their stately, tall flower spires, are a popular perennial choice for adding vertical interest to garden beds. Delphiniums absolutely can self-seed, but the success of this process varies significantly based on the plant’s genetics and the specific environment of your garden. Self-seeding is a natural propagation method, yet its effectiveness is highly dependent on factors like local climate, soil conditions, and the gardener’s cultivation practices. Understanding the mechanics of how and when a delphinium releases its seed is the first step in either encouraging or preventing new volunteer plants.
The Process of Delphinium Self-Seeding
Delphiniums are naturally prolific seed producers, provided the spent flower stalks are left intact to mature. After the petals fade, the plant directs its energy into forming small, dry seed pods along the flower spike. These pods start green and gradually turn a light brown color as they dry out, typically occurring in late summer to early fall.
When fully mature and dry, these seed pods will often split open, releasing the small, dark seeds within. Seed dispersal usually relies on physical means, such as wind shaking the tall stalks or raindrops knocking the seeds onto the soil surface below. A single main flower spike can contain hundreds, sometimes over a thousand, of these tiny seeds.
The viability of naturally dispersed delphinium seeds is often lower than commercially packaged seeds due to exposure, but a certain percentage will still germinate. Successful natural germination requires the seeds to be exposed to cold temperatures, a process known as cold stratification, which breaks their dormancy. The newly dropped seeds need to overwinter in the soil before they can sprout the following spring.
Managing Seed Production in the Garden
Gardeners have significant control over delphinium self-seeding through the practice of deadheading. Deadheading involves removing the spent flower spike before the seed pods fully mature and dry out. This action prevents the plant from expending energy on seed creation, which can instead encourage a second, smaller flush of blooms later in the season.
To prevent unwanted self-seeding, the entire stalk should be cut off near the base of the plant, or just above the first set of healthy leaves, once flowering is complete. If the goal is to encourage natural self-seeding, leave the flower spike on the plant until the pods are visibly dry and brown. Allowing the seeds to drop onto bare soil or a lightly mulched area in the fall provides the necessary conditions for natural stratification over winter.
For those who wish to collect seeds for controlled planting, they should be harvested when the pods are fully dry and beginning to crack open. The collected seeds can then be stored in a cool, dark place, often requiring artificial chilling in a refrigerator to mimic the winter stratification process before planting in the spring. This intervention allows for more predictable germination rates compared to random self-seeding in the garden bed.
True-to-Type: What to Expect from Seedlings
The genetic outcome of resulting volunteer plants is a key consideration with delphinium self-seeding. The vast majority of commercially available delphiniums are complex hybrids, developed by crossing different parent plants to achieve specific colors, sizes, and flower forms. When a hybrid plant self-pollinates, the resulting seeds are not guaranteed to produce offspring identical to the parent plant.
The term “true-to-type” refers to the ability of seeds to reliably produce plants that look exactly like the parent. Since most delphinium cultivars are hybrids, their self-seeded offspring will likely exhibit genetic variability, meaning they will not come true-to-type. This phenomenon results from the hybrid genetics reverting back to the traits of their various ancestors.
Gardeners should expect a wide range of variation in the self-seeded plants, often involving differences in flower color, height, and bloom structure. Colors may revert to more common shades of basic blue and purple, and the sophisticated flower forms of the hybrid parent may become simpler. If a gardener wants an exact replica of a favorite named variety, they must propagate it through asexual methods like division, not by seed.