Crosses between various species and genera in the Oncidiinae tribe, have resulted in plants that have come a long way from the original species in beauty and ease of culture. These plants start blooming small with spikes of fancifully patterned flowers in shades of white, yellow, red and brown, and as they mature become large, robust plants with long stems of flowers.
Healthy Oncidiums start with healthy roots:
- Pot in a fine medium. Fir bark mixtures are best, with 0.5 to 1.0 cm chunks of bark, perlite and charcoal.
- Report when the medium starts to break down or when the new
growth will be over the edge of the pot. - Remove old medium if it is loose, any rotting roots or brown bulbs; choose a plastic pot that will allow for 2 to 3 new growths and position in the pot so that the new growths will grow from the middle to the edge.
- Roots should dry out somewhat between watering. When the plant is actively growing, water when medium has just begun to dry out but is still slightly damp. When the plant is completing its growth start to let it dry more, to encourage flowers rather than vegetative growth. When it is dormant, typically in winter, do not water until medium is almost completely dry. When watering, water thoroughly, with a volume of water at least equal to that of the pot.
- Do not use water softened in salt-consuming water softeners. Low mineral water is preferred, such as naturally soft water or rain water. If hard water is used, water very heavily to flush minerals.
- Fertilize weakly and frequently with a balanced fertilizer. One-eighth to one-quarter strength recommended by manufacturer for house plants every week in spring and summer and every two weeks in autumn and winter.
Healthy leaves produce more and bigger flowers:
- High light levels are appropriate. Leaves should be a light green, not yellowish (too much light) or dark green (too little light). They should be firm, not long and floppy (more light needed). A slight red blush indicates an ideal light level on some plants. A more pronounced red blush will indicate too much light.
- Four hours of sunshine on a windowsill (West or South) or 6-12” under an eight tube fluorescent fixture or under an HID sodium or metal halide lamp. Plant size usually prevents mature plants growing under fluorescent lights.
- Recent pseudobulbs should be firm; if wrinkled, check roots for rot, and report if necessary. High humidity (such as enclosing the plant in a plastic bag) will aid recovery if most or all of roots lost, but be careful of rot.
- Oncidiums do best with 50-60% humidity but when mature will grow and bloom, although more slowly, in lower humidity. Use humidifier to raise humidity – humidity pans and misting minimally effective. Enclosing plant growing areas is effective but ensure fresh air and air movement to avoid mold and rot.
- Grow Oncidium hybrids in intermediate temperatures with 14°C minimum winter nights and 29°C summer day maximum. Ensure 6-12°C day/night difference to aid flower formation.
- Some varieties prefer slightly different temperatures:
- Warmer temperatures: Brassia hybrids, including Miltassia, Beallara and Maclellanara.
- Cooler temperatures: Odontoglossum hybrids, including Vuylstekeara and Odontioda.
Oncidiums usually bloom annually and the flowers individually last for three or more weeks:
- Maintain plant orientation while spike is growing for best display.
- Oncidiums often provide much superior flower size and color as mature plants than as first bloom seedlings.
- Buds turning yellow, wilting and falling prior to opening is from not enough energy in the plant to open the flower either because the light is too dim, the plant is too small, or the roots have rotted. Also due to ethylene gas (given off by ripening fruit), or large temperature changes.
