Hydrangeas are most commonly propagated through cuttings, but these popular shrubs also produce true seeds, offering a unique way to grow new, genetically distinct plants. While the large, showy blooms are the main attraction, the seeds themselves are tiny and easily overlooked. Locating and identifying the seeds requires a closer look at the dried flower structure where they are housed.
The Seed Capsule Structure
Hydrangea seeds mature within a small, dry fruit known as a capsule, which develops from the fertile flowers inside the bloom clusters. These fertile flowers are often inconspicuous, especially in mophead varieties where large, colorful sepals overshadow them. Lacecap, smooth, and oakleaf varieties offer a better chance of finding fertile flowers that will develop viable seeds.
The capsule begins to form during the late summer and matures as the flower head fades, dries, and turns brown. This protective structure becomes brittle and papery, a sign that the seeds inside are fully ripe. Seed collection is best done in the late autumn or early winter after the flower heads have completely dried on the plant.
Visual Characteristics of the Seed
Hydrangea seeds are extremely small, often described as similar in size to fine dust or cracked black pepper. Their size means a white background is necessary to distinguish them from debris or soil particles. The seeds measure less than one millimeter in length, making them challenging to handle without magnification.
The color of a mature, viable seed ranges from pale tan or beige to dark brown or black. Their shape is oblong, tear-dropped, or slightly irregular, rather than perfectly round. Some species, like Hydrangea paniculata, produce long, spindle-form seeds featuring a narrow, wing-like structure at both ends. This structure aids in wind dispersal, differentiating them from the flatter, more compact seeds of other Hydrangea species.
Collection and Preparation for Sowing
To successfully collect the seeds, wait until the flower heads are completely dry and feel papery to the touch. Carefully clip the dried flower heads from the plant and place them inside a paper bag. Allowing them to dry for an additional few days ensures maximum seed release before extraction.
The seeds are extracted by gently shaking or lightly crushing the dried flower head inside the bag. Pour the contents onto a white plate or sheet of paper to easily spot the tiny, dark specks.
For successful germination, the seeds should be surface-sown on moist, sterile potting mix and should not be buried, as light is often required to trigger the germination process. Some varieties benefit from a period of cold stratification, which mimics winter conditions and helps break seed dormancy.