There are six main techniques currently used to propagate orchids and these are: division, back bulbs, keiki, aerial cuttings, meristem or tissue culture, and seed. All of the techniques are discussed in detail below and all but two are commonly employed in the home or greenhouse. The two which aren't commonly employed at home are propagation by seed and meristem tissue culture as these need laboratory conditions to maintain sterility.
PROPAGATION OF ORCHIDS
There are six main techniques for orchid propagation: division, back bulbs, aerial cuttings, keiki, meristem or tissue culture, and seed. For example, Cymbidiums can be grown from back bulbs (pseudo bulbs) and Crucifix orchids can be grown from stem cuttings. Dendrobiums can be grown by division offsets or separation. Well developed plants of terrestrial orchids (such as Paphiopedilum) can be divided just before active growth begins.
Epiphytic orchids are usually sympodial or monopodial in growth:
- Sympodial ... the plant axis is horizontal, new growth comes from lateral buds produced at the base of pseudobulbs of old plants. These include Cattleya, Cymbidium and Odontoglossum. When the plant is overgrown in the pot, the rhizome attached to the pseudobulb can be partly cut and left till new growth begins on it... or completely severed and the pseudobulb planted separate to the rest of the plant immediately ... with cattleyas each new plant should have 3 or more pseudobulbs. With Cymbidiums, one pseudobulb is sufficient for a new plant.
- Monopodial… the axis is vertical; the main growing tip extends upwards producing leaves in a 2 ranked arrangement. Vandas are monopodial. White aerial roots develop on the stems as they grow upwards. When the stems have a good development of these aerial roots, sections of stem can then be taken as stem cuttings ‑ roots can be left on such cuttings.
One very important characteristic of seed reproduction is that variation can occur within a group of seedlings. A plant grown from a seed might not be exactly the same as the plant from which that seed was collected. By far the greatest number of orchids are propagated by asexual means, as this ensures that the offspring are genetically identical to the parent plant. Seedling orchids are grown to either:
- Provide seedling plants.
- Breed new plants....growing seedlings is the most important way of developing new varieties. This is an important field in orchid culture, with many hybrids and intergeneric crosses being bred to exhibit new and different physical characteristics.
Hybrid Seed Production
An F1 Hybrid plant is produced from seed which is obtained from cross pollination between two different species or two different varieties of the same species. Hybrid seeds can be produced the following ways:
- By hand pollination. This is usually used to produce new varieties for testing purposes. (ie: Most new varieties are obtained this way).
- Production in seed plantations. Two different varieties are interplanted or placed in an area and seed collected from those plants.
- Chance seedlings. Seed is collected from plants i the wild or elsewhere which are suspected to have cross pollinated with different varieties. The seedlings are grown on to flowering stage, then the best varieties are selected.
- Seed collected from F1 Hybrid plants. The initial hybrid is produced by cross pollination (ie: as above). This hybrid is grown until it produces seed, and the seed is then collected. This seed is second generation hybrid seed (thus it is known as F2 seed). New plants are grown as seedlings from this seed.
Harvesting Orchid Seed
Orchid seed is not generally bought. You either breed it or collect it yourself, and normally sow as soon as possible. As the pods mature they change colour, usually yellowing, then start to show signs of splitting along the placenta. The plants must be watched carefully. At this stage, and not before, harvest the seed into a polythene or paper bag. Off one plant you may have as many as a million or so viable seed, or as few as a dozen. (eg: There can be nearly 3 million seeds in one pod of a Cymbidium tracyanum)
Seed should be shaken in Chloros (usually 1 in 20 with water) for 10 minutes before planting to kill any disease. Sow using droppers or needles in a sterile environment, into flasks. Seal and place in high humidity, warm environment (70 to 80 degrees F). It normally takes 4 ‑ 6 months to raise seedlings to the point where they can be transplanted. It can take 4 ‑ 10 years for the seedlings to flower.
Seeds are alive and like any living thing they can be harmed by adverse conditions. Storing at room temperature does not work. Storing in a refrigerator can be successful under the right conditions.