Hydrangeas are ornamental shrubs cherished for their large, showy blooms. While these plants are most commonly propagated using stem cuttings, collecting and sowing seeds offers an alternative method for reproduction. This process is valuable for plant breeders seeking new cultivars or for gardeners interested in genetic variability. Harvesting and processing hydrangea seeds involves precise timing and careful steps to ensure the viability of the reproductive material.
Understanding Hydrangea Seed Production
The ability of a hydrangea flower head to produce viable seeds depends on its floral structure. Flower clusters, known as inflorescences, are composed of two types of flowers: large, sterile florets and tiny, fertile florets. Most popular “mophead” cultivars of Hydrangea macrophylla maximize the showy sterile flowers, meaning they often yield few fertile seeds.
The best candidates for seed collection are “lacecap” varieties, which feature a central cluster of small, fertile flowers surrounded by sterile ones. Species like Hydrangea paniculata (panicle hydrangea) and Hydrangea quercifolia (oakleaf hydrangea) also contain a mixture of fertile and sterile flowers, making them reliable seed producers. Seed maturation occurs in the fall, eight to twelve weeks after the blooms have faded and dried out on the plant. The flower heads must be completely dry and brittle, indicating that the seeds inside the small, dark capsules are ripened.
Harvesting and Initial Processing of Seed Heads
Harvesting the seed heads should be timed for late fall after the flowers have turned completely brown and papery. Using clean, sharp pruners, clip the dried flower heads from the shrub, leaving a short section of stem attached to the cluster. This stem provides a convenient handle for the next drying stage and helps prevent the flower head from shattering prematurely.
Immediately place the harvested flower heads into individual brown paper bags, especially if collecting from different species or cultivars. Paper bags are preferred over plastic because they absorb remaining moisture, preventing mold development that would ruin the seed lot. The bags should be labeled immediately with the date and the plant’s identity to maintain an accurate record.
The intact seed heads must undergo a final drying period indoors to ensure maximum brittleness, which simplifies subsequent seed extraction. Hang the paper bags in a cool, dry, and well-ventilated area, such as a garage or dry basement, for one to two weeks. This ensures that the seed capsules are fully desiccated, allowing for easy separation of the tiny seeds from the surrounding plant debris.
Extraction, Cleaning, and Storage
Once the dried flower heads are fully crisp, the process of extracting the seeds can begin. Empty the contents of a single bag onto a clean, flat surface, such as a white plate or sheet of paper, which makes the dark, minuscule seeds easier to see. The seed capsules must be broken open by gently crushing the brittle floral material between your hands or by vigorously shaking the contents in a closed container.
Separating the seeds from the chaff (the remaining debris of petals and capsules) requires a delicate technique due to the seeds’ small size. A simple method is to use a fine-mesh sieve, such as a tea strainer, which allows the seeds to pass through while trapping larger plant fragments. Alternatively, winnowing can be employed by carefully blowing across the seeds and chaff, carrying away the lighter debris while the heavier seeds remain.
Storage and Stratification
After cleaning, the seeds must be thoroughly air-dried for several days at room temperature before packaging for long-term preservation. For optimal viability, store the dried seeds in a small paper envelope or a tightly sealed glass jar in a cool, dark, and dry location, such as the crisper drawer of a refrigerator. Storing them in a refrigerator at a consistent temperature between 33 and 41 degrees Fahrenheit helps maintain dormancy. Before planting in spring, hydrangea seeds benefit from cold stratification, which involves keeping them in a cold, moist environment for four to six weeks to break dormancy and encourage germination.