Seed storage and germination parameters
There has been a remarkable amount of research that has been performed with respect to keeping orchid seeds alive. For the vast majority of growers, the parameters listed below will be enough to
maximize the germinability of your orchid seeds.
Seeds must not be excessively moist when packed into storage. Any excess moisture, such as from green parts of capsules, moist or damp seed, or damp packing materials, will cause fungi and bacteria
to breed. Even if the organisms are not harmful to the seeds themselves, they will contaminate your seed to the point that it cannot be effectively disinfected, and all of your flasks will be
The ideal temperature for seed storage is at 4o C. At this temperature, seeds of some species have germinated after more than 25 years in storage. Although not all species will last this long (it is an effort to keep some genera alive for more than 4 months, even under the best of conditions), the longevity of many common genera are maximized at this temperature.
Most household refrigerators will go this low (best of all, your milk will last forever at this temperature). The seed stored here at the OSP is stored in large plastic food storage tubs, sealed carefully
to maintain the correct atmosphere (see below).
Keeping orchid seed dry is important, but it is possible to keep seed too dry. Research and trial and error has shown that approximately 30% relative humidity (RH) is optimal at this temperature. This level is best maintained through the use of "constant humidity solutions," consisting of a small glass jar (about 4" across, 4" deep) that has calcium chloride mixed with a small amount of water in the bottom.
Constant humidity solutions will absorb extra water when it becomes available, dropping the RH to an acceptable level, provided there is still more undissolved solid present. Similarly, it will raise
the humidity as moisture leaves, provided there is still liquid water present in the slurry. In this manner, the proper amount of water remains in the atmosphere inside the storage units.
The seeds are carefully dried and inspected for any signs of mold, fungi, and insects before being added to the collection. The 30% relative humidity ensures the seeds are not damaged from
extreme dryness, nor from water damage or loss due to rot.
When you receive your package of seeds, unless they contain green capsules, they can be placed in the refrigerator until used. We are often asked for how long they are stable like this.
The question is now how long they are good for, but how well you wish they would germinate. The fresher the seed, the better (except for most cold-tolerant terrestrial orchids, which may require
strange and peculiar cold dormancy periods. We ship Cypripedium species only after they have received a minimum of 4 months in refrigeration, unless noted otherwise.).
For germination, we use P-668 (PhytoTechnology) or P-6668 (Sigma) seed germination media, which is similar to 1/2 strength Murashige and Skoog. The disinfection solution used most often
consists of 5 grams of dichoroisocyanuric acid (DCCA) added to 1 liter of distilled water, along with 1-2 drops of a wetting agent added. The DCCA solution keeps for several months when stoppered
tightly and refrigerated in clean glass. The wetting solution is made by adding 2 drops of antibacterial "Dawn" dishwashing detergent to 100 mL of distilled water; this is tightly capped,
and kept refrigerated.
We have also used calcium hypochlorite, sodium hypochlorite, and 'Virkon S' for disinfection of seeds. Our current use of DCCA is the result of experimentation, and our current
whims. It does not necessarily reflect success or failure with any one solution.