Orchid seeds are fundamentally different from the seeds of most other flowering plants. They are microscopic, often described as dust, and are dispersed by the wind in massive numbers. They lack the endosperm, which is the internal food storage that nourishes a typical germinating seed. This absence means that an orchid embryo cannot sustain itself long enough to establish a root and leaf system in standard soil.
Unique Requirements for Germination
In their natural habitats, orchid seeds overcome the lack of internal food by forming a relationship with specific mycorrhizal fungi, known as symbiotic germination. The fungi penetrate the seed and provide the necessary carbohydrates and nutrients that the embryo digests to begin growth. Consequently, orchid propagation for commercial and hobbyist purposes relies on asymbiotic culture, which replaces the fungal partner with a sterile, nutrient-rich growth medium. This technique involves culturing the seeds in a sterile flask on a gelled substance, typically agar, that contains all the necessary elements for the seed to grow independently.
Preparing the Sterile Environment and Media
Successful asymbiotic germination depends entirely on maintaining a sterile environment to prevent contamination. The nutrient-rich agar medium, designed to feed the orchid embryo, is equally appealing to undesirable microorganisms. Flasks or specialized containers must be filled with a prepared nutrient solution, such as a commercially available orchid mix or a standardized formula like Murashige and Skoog (MS) media, which contains macro- and microelements, vitamins, and a sugar source. The liquid medium must be sterilized after being poured into the containers and before the seeds are introduced. This is accomplished by using a pressure cooker or an autoclave to heat the sealed containers to 121 degrees Celsius for 15 to 20 minutes, killing all microbial life, and then allowing the flasks to cool completely to solidify the agar while remaining sealed.
Seed Sterilization
Before sowing, the seeds themselves must undergo a sterilization process, as dry seeds collected from a mature pod are covered in surface microorganisms. A common and effective method involves immersing the seeds in a diluted solution of household bleach (sodium hypochlorite), often at a concentration of 0.5% to 1.0%. A few drops of a surfactant, such as a mild dish soap, are added to reduce the surface tension, allowing the solution to fully saturate the microscopic seeds. The seeds are agitated in this solution for 10 to 20 minutes before they are ready for transfer to the sterile flask.
The Aseptic Sowing Procedure
The transfer of the sterilized seeds onto the nutrient media must take place within an isolated, clean-air environment to prevent recontamination. A laminar flow hood is the most effective tool, but a still-air box or homemade glove box can be used by hobbyists. This enclosed space minimizes the risk of airborne spores settling on the open medium. Once inside the sterile workspace, the flask is opened only for the brief moment required to introduce the seeds. The seeds, suspended in the bleach solution, are transferred using a sterile tool, such as a flamed wire loop or a pipette. The goal is to distribute the seeds thinly and evenly across the surface of the cooled agar, avoiding thick clumps that will impede growth. Immediately after sowing, the flask opening must be sealed with a sterile cap or stopper to maintain the aseptic environment. This sealing prevents any subsequent entry of contaminants that would rapidly colonize the nutrient-rich agar.
Deflasking and Early Seedling Care
After sowing, the sealed flasks are placed under controlled conditions to encourage germination, typically requiring temperatures between 20 to 25 degrees Celsius and continuous or long-day exposure to gentle, indirect light. Germination is visible as the seed embryo swells to form a protocorm, a small, undifferentiated ball of tissue that absorbs nutrients from the media. This initial growth phase can take several weeks to many months, depending on the orchid species.
The seedlings remain in the flask until they develop sufficient size and structure, which usually means they have grown two or three small leaves and possess a rudimentary root system. This removal process, known as deflasking, is a transition from a 100% sterile, high-humidity environment to the non-sterile outside world. The plantlets are carefully extracted and gently washed in room-temperature water to remove all traces of the agar media, which could otherwise serve as a food source for destructive fungi and bacteria.
The newly deflasked seedlings require a gradual acclimatization process called hardening off. They are typically potted together in shallow community pots using a fine-grade, moisture-retentive medium like finely chopped sphagnum moss or small bark chips. To maintain the high humidity the plantlets are accustomed to, the pots are immediately placed inside a covered container or plastic bag, which acts as a humidity dome. Over the next few weeks, the cover is slowly lifted or vented to reduce the humidity gradually, allowing the young orchids to adjust before being exposed to normal growing conditions.