Dahlias are beloved garden flowers often grown from tubers, which guarantees a perfect copy of the parent plant. Cultivating dahlias from seed offers a thrilling opportunity for surprise, often called the “seed lottery.” Each seed carries a unique genetic blueprint, meaning you could discover a brand new flower form or color. This process involves shifting focus from encouraging new blooms to allowing the flowers to fully mature and set viable seed for the next growing season.
Understanding Dahlia Seed Production
Growing dahlias from seeds uses sexual reproduction, which is fundamentally different from the asexual cloning achieved with tubers. Planting a tuber creates a genetic clone, ensuring the resulting flower is identical to its parent. Conversely, a dahlia grown from seed is a hybrid, inheriting genes from two parent plants, resulting in a unique, diverse flower.
This genetic variability is high because dahlias are polyploids, possessing eight sets of chromosomes, which allows for millions of possible combinations. For a seed to form, the central disc florets of the flower must be pollinated, typically by bees or other insects. After successful pollination, each fertilized ovule at the base of the flower’s ovary develops into a seed, and a single seed head can produce dozens of unique seeds.
Recognizing Mature Seed Heads
To successfully collect dahlia seeds, you must stop removing spent blooms, or deadheading, roughly six to eight weeks before your first expected frost. This allows enough time for the flower to be pollinated and for the resulting seed pod to fully mature on the plant. The seed head, which is the remnant of the flower after the petals have dropped, will begin to change shape and color.
Initially, the seed head will appear green and firm, but a mature, viable pod should become pointed and start to dry out. The color will transition from green to yellow and eventually turn completely brown and papery. A simple test for readiness is to gently squeeze the pod; if any moisture or liquid drips out, the seed inside is still immature and not ready for harvest. If the seed head is completely brown and dry, it is ready to be cut from the plant.
If a hard frost is imminent, you can cut the seed heads slightly earlier, even if they are still green, provided they feel firm. These immature pods can be placed in a vase indoors to continue drying, though the seeds will not develop further once separated from the parent plant. The goal is a pod that has completely dried down into a hard, acorn-like structure.
Harvesting and Extraction Steps
Once the seed heads are mature and dry, harvest them by snipping the pod off with a short stem attached. Place the harvested seed heads in a paper bag or spread them out on a tray in a cool, dry, and well-ventilated location for final drying. This ensures any residual moisture evaporates, preventing the seeds from developing mold during storage.
After about one to two weeks, the seed heads should be brittle and papery to the touch. To extract the seeds, gently break open the dried pod. The viable seeds will be nestled inside, often still mixed with the dry, papery flower parts.
The next step involves separating the seeds from the dry material. You can do this by rubbing the dried material between your fingers over a shallow container or plate. Viable dahlia seeds are flat, hard, elongated, and typically dark brown to black. They must be hard and should not bend or feel soft when pressed, as this indicates they are not viable. For final cleaning, gently blow across the pile of material; the lighter chaff will fly away, leaving the heavier seeds behind.
Preparing Seeds for Long-Term Storage
The longevity of dahlia seeds depends on proper drying and storage conditions. After cleaning, the seeds must be completely dry before being packed away, as moisture promotes mold growth and reduces viability. Store the seeds in small paper envelopes or bags, which ensure breathability and help regulate moisture fluctuations.
Clearly label each packet with the name of the dahlia parent plant, if known, and the year the seeds were collected. The ideal storage environment is one that is cool, dark, and dry, with consistent temperatures. Storing the envelopes inside an airtight container in a refrigerator, where temperatures are consistently low, around 40°F (4°C) or less, can significantly extend the seeds’ ability to germinate for future seasons.