Coneflowers, scientifically known as Echinacea, are popular perennial plants prized for their hardiness and distinctive flower heads. Saving seeds from these garden favorites allows for easy propagation and sharing, but it requires a crucial step: cleaning them. The seed heads contain a mix of viable seeds and plant debris, collectively known as chaff (including dried petals and spiky bracts). Removing this chaff is necessary because it improves seed viability in storage, prevents mold growth, and ensures a cleaner planting experience.
Preparing the Cones and Extracting Seeds
Before any separation can occur, the harvested flower heads must be completely dry, a process often called curing. Cut the mature, brown, and brittle seed heads from the plant, leaving a few inches of stem attached for easy handling. Lay the cones on a mesh screen or place them loosely in a paper bag in a well-ventilated, dry area away from direct sunlight for about two weeks to ensure they are fully desiccated.
Once cured, the seeds must be physically released from the tough cone material through threshing. A highly effective method involves placing the dried heads into a sturdy container, securing the lid, and shaking vigorously for about 30 seconds. This friction helps to break the seeds free from the cone structure and the sharp, central spikes. Alternatively, rub the cones over a wire screen or against a rough surface. This hands-on method can be uncomfortable due to the cone’s texture. Threshing results in a concentrated pile of seeds mixed with large pieces of cone material and fine chaff.
Essential Methods for Separating Chaff
The mixed material resulting from threshing requires a multi-step approach to achieve a clean seed sample, utilizing differences in size and weight. The first and most straightforward technique relies on air movement to separate the light chaff from the heavier seeds.
Air Separation (Winnowing)
Winnowing is an ancient method that leverages gravity and air to clean seeds. To perform this, place the seed and chaff mixture in a shallow container, such as a baking sheet or wide bowl, and stand outside on a calm day or near a gentle fan. Carefully pour the mixture from one container into another, allowing a slight breeze or fan air to blow through the stream of falling material. The lighter pieces of chaff will be carried away by the air current, while the denser, heavier seeds fall straight down into the second container.
Controlling the height of the pour and the strength of the airflow is important. A fan set on a low speed, placed a few feet away, often provides the most consistent airflow for indoor cleaning. Repeat this process several times, gradually increasing the height of the pour to remove progressively finer and lighter particles. This technique eliminates the bulk of the fluffy debris and dust.
Size Separation (Screening)
After winnowing removes the lightest debris, screening, or sifting, is used to separate materials based on size. Coneflower seeds are elongated and relatively small, requiring a sequence of different mesh sizes for cleaning. Begin with a coarse screen or kitchen colander that has holes large enough for the seeds to pass through, but small enough to catch the largest pieces of broken cone and stem fragments.
Next, use a fine mesh screen or sieve, which will allow very fine dust and sand-like debris to fall through while retaining the seeds. Using two screens—one for large material and one for seeds—will eliminate nearly all physical contaminants. A mesh size of approximately 1/8 inch will likely filter out the largest remnants, followed by a fine screen of about 1/16 inch to keep the seeds while discarding the dust.
Density and Water Testing
Some seeds can be separated using water, where viable seeds sink and empty chaff floats, but this method carries risks for Echinacea. Coneflower seeds can be damaged by prolonged moisture exposure, and they must be dried immediately after any water test. Given the effectiveness of winnowing and screening, using water is generally not recommended for home gardeners. It is more efficient to rely on the density difference between the seeds and dry chaff using air separation.
Post-Cleaning Handling and Storage
Once separated from the chaff, the seeds require a final drying period before storage. Even clean seeds may hold residual moisture that can lead to mold if not completely removed. Spread the cleaned seeds in a single layer on a paper towel or plate for an additional two to three days in a dry, room-temperature environment.
Proper storage maintains seed viability and ensures high germination rates. Use breathable containers like paper envelopes or small glass jars to minimize moisture buildup. Avoid using plastic bags or airtight plastic containers unless you are certain the seeds are bone-dry, as trapped humidity is the primary cause of spoilage. Store the labeled containers in a cool, dark, and dry location (40 to 60 degrees Fahrenheit), such as a refrigerator or unheated garage. This cool environment mimics the natural winter conditions many perennial seeds require to break dormancy.