Green Pod Harvesting of Rhododendron Seed
Reid Bohnson, M.D., Winston Salem, North Carolina
Harvesting of seed pods prior to the fully ripened stage is practiced successfully in orchid seed culture. Viable seed in Cattleya orchids can be obtained in 5 months instead of waiting for normal ripening at 9-10 months. This procedure is adaptable to rhododendrons, allows earlier seed sowing and preserves all of the available seed, seed which may be dispersed in the normally opening seed capsule.
During the past three growing seasons, this method has been practiced on hand pollinated crosses of commercially available elepidote rhododendrons with successful germination in 43 out of 49 seed pods. The average period of time of collection after pollination has been from 105 to 135 days (May to September). The shortest successful period has been 66 days after selfing of a fall flowering blossom of Elizabeth.
The plump seed capsule, which along with its pedicel may be beginning to turn slightly yellow, is placed in a glassine envelope (available from your hobby shop which sells stamps) labeled as to cross and date. The envelopes are placed in a re-sealable air tight wide mouth jar (a peanut butter jar does very well) over a desiccant containing a color indicator for drying activity. A suitable desiccating agent is Drierite (available from Scientific Products, McGaw Park, Il., Catalogue No. D8155 or Curtis Matheson Scientific, Houston, Tex., Catalogue No. 116-582 at $2.65 per pound or Fisher Scientific Products, Pittsburgh, Pa., Catalogue No. 1-952-5 for a 3" disc at $1.65).
The jar is then placed in a warm environment to enhance drying. After 5 to 7 days, the pod is thoroughly dried. The dried seed pod, which may have started opening at the end, is taken and the dried style is removed. With a sharp pen knife, a small round slice of the base of the capsule is cut away. The 5-10 valves of the capsule are then identified and cut gently longitudinally along the groove which separates each section. This groove is the site of the normal splitting of the ripe capsule. The seed appears in each hollow valve, can be tapped out or gently scraped out with the point of the knife blade. A minimum of chaff is obtained; the larger particles can be separated with tweezers.
The harvested seed may be immediately sown or may be stored in the air tight desiccating jar in a refrigerator. The desiccating granules are formulated with an indicator which changes color on loss of drying activity. Activity can be restored by heating in an oven or a toaster grill at 300 degrees F.
Further study and data is needed to determine the minimum time for viable seed, which will undoubtedly vary as to series and species.
Editor's Note: The Seed Exchange Director requests that green harvested seed be thoroughly cleaned before being sent to the Seed Exchange.