The genus Rudbeckia, which includes popular garden flowers like Black-eyed Susan and Gloriosa Daisy, is known for its bright, sun-like blooms and distinctive central cone. Knowing the precise appearance and location of the seeds is the first step in successful propagation.
Detailed Physical Description of Rudbeckia Seeds
Rudbeckia seeds are remarkably small, measuring approximately 1 to 2 millimeters in length. They possess a distinct shape that allows them to pack tightly into the flower’s central cone. They are typically oblong, appearing wedge-shaped or somewhat angular, often with four discernible sides.
The color of a mature seed is dark, generally ranging from black to a deep charcoal-gray or dark brown. They possess a smooth, hard exterior and a slightly glossy finish. Unlike the seeds of many other plants in the Aster family, Rudbeckia seeds lack the feathery tuft of hairs (pappus), which aids in wind dispersal. This absence means the seed itself is a simple, dense unit that relies on gravity or animal activity to move away from the parent plant.
Locating and Collecting the Seeds
The seeds are found exclusively within the hardened, dome-shaped center of the Rudbeckia flower, often referred to as the cone or disc. For the seeds to be viable for collection, the flower must be fully spent and completely dry on the stalk. The petals, or ray florets, will have shriveled and fallen off, leaving only the central structure.
The cone itself changes color as the seeds mature, transitioning from a soft green or brown to a rigid, dried-out, dark brown or black. This process typically takes about three to four weeks after the bloom has finished. The best time to harvest is when the cone feels firm and brittle, and the seeds inside have turned charcoal-gray.
To collect, cut the dried seed heads and place them in a paper bag to dry for a few more days, ensuring all moisture has evaporated. The seeds are then easily released by rubbing the cone between your fingers or vigorously shaking the dried heads inside the bag.
Storing and Sowing Rudbeckia Seeds
After collection, the seeds must be completely dry before storage to prevent mold and maintain viability. Store the dried seeds in a clearly labeled paper envelope or a sealed container placed in a cool, dark, and dry location.
Successful germination of many Rudbeckia species requires a period of cold, moist conditioning known as cold stratification. This process mimics the natural winter cycle and helps break the seed’s dormancy. You can achieve this by mixing the seeds with moist sand or a damp paper towel in a sealed plastic bag and placing them in a refrigerator for 30 days to three months.
When sowing, whether indoors or directly outside, the tiny seeds should be planted very shallowly. They should be placed only about 1/16 of an inch deep, or simply pressed onto the soil surface, as they require light to germinate.