Obtaining viable seeds from geraniums requires precise timing and attention to the plant’s unique method of seed dispersal. While the name “geranium” is often applied to the common annual bedding plant (Pelargonium), this guide focuses on harvesting seeds from the true, hardy perennial geranium (Geranium species), often called cranesbill. The perennial type is known for its particularly rapid seed ejection mechanism. Successful propagation begins with recognizing the specific anatomy and visual cues of seed maturity on the plant.
Identifying the Seed Structures
The seeds of a true geranium develop within a distinctive structure that replaces the spent flower, earning the plant its common name, “cranesbill.” This structure is an elongated, beak-like capsule, or rostrum, formed from the fertilized flower’s style and ovary base. At the base of this long spike, five small segments, called mericarps, each contain a single seed.
Observing the change in this structure determines the optimal moment for harvest. Initially, the cranesbill is green and firm, but as the seed inside matures, the entire structure begins to dry out and darken. The spike and the small seed cases will turn from green to a dark brown or black color, signaling ripeness.
Timing is important because the geranium has evolved a method of explosive seed dispersal. Once fully dry and ripe, the five segments of the mericarp rapidly split away from the central column, flinging the seeds outward up to several feet. Missing this small window means the plant will launch its seeds, leading to complete harvest failure. The perfect moment to collect is when the structure is dark and dry, but before it has begun to coil, split, or spring open.
Collecting the Mature Seeds
Harvesting geranium seeds requires securing the ripening seed heads before they reach the point of explosive dehiscence. The most reliable method involves placing a small, breathable covering over the individual cranesbill structures.
Fine mesh bags, such as organza or nylon stockings, contain the seeds while allowing air circulation and drying. Secure these coverings around the stalk just below the seed head when the rostrum is fully formed but still green or starting to turn brown. A small piece of cheesecloth or a rubber band placed tightly around the beak can also prevent the outer segments from flinging their contents.
Once the structure inside the covering has dried completely and turned dark—a period that may take a few weeks—cut the entire stalk with scissors or sharp shears. Cutting is important because pulling can prematurely trigger the seed ejection mechanism. Place the collected stalks in a paper bag or envelope indoors to finish drying and allow any remaining seeds to release naturally.
Preparing Seeds for Planting and Storage
Cleaning and Drying
After collection, seeds must be cleaned and thoroughly dried to ensure long-term viability and prevent mold growth during storage. The seeds are small and dark, sometimes attached to a fine, feathery filament. Separate this chaff and debris from the seed through winnowing, which involves gently rolling the material between your fingers over a piece of white paper.
Storage
Allow the cleaned seeds to air-dry completely for several days at room temperature before packaging. For long-term storage, place the seeds in a paper envelope or breathable container. Store them in a cool, dark, and dry location that maintains a consistent, low temperature, such as a refrigerator, to preserve seed vigor.
Cold Stratification
Hardy geranium seeds possess dormancy requiring a period of cold, moist conditions to initiate germination. This process, known as cold stratification, mimics the natural winter cycle. To perform this artificially, mix seeds with a slightly damp medium like sand or vermiculite. Place the mixture in a sealed plastic bag and refrigerate at 33 to 41 degrees Fahrenheit for about 60 days. This chilling period breaks dormancy and significantly improves the rate of successful sprouting.