This group of orchids used to be known as Odontoglossum (tiger orchids). Now classified as Oncidium, they should not be confused with the orchids traditionally bearing this name that need warm growing conditions. See Oncidium orchids (warm section) for details of these.
To get the best results from Oncidium, it is important to get the basics right. Finding a good position and watering correctly will usually ensure they do well.
Oncidium (cool-growing types) grow under filtered, subdued light (11,000-16,000 lux). In the home they do best in a north- or north-east facing window. Do not place them in the middle of the room as this is likely to be too shady.
In the greenhouse, they need shade from late March until the end of September.
Most hybrids grow continuously all the year round and so are fed throughout.
- From February until August, feed with high nitrogen (20:10:10 for example), using it at half strength at every second watering
- From September until February, feed with a fertiliser higher in potassium (such as 4:4:8), using it at half strength at every second watering
- A foliar feed can occasionally be applied to the leaves to act as a tonic
Watering and humidity
- Check then water (every 5-7 days) all the year round if they are being grown as houseplants
- In the greenhouse, water every 4-7 days from the end of February until September, depending on weather conditions
- During October and November when not much heat is needed and light is reduced, they may go 10-14 days between watering
- From December until the end of February when heating is on, you will need to water every 7-10 days
The ideal humidity is between 60-70 percent, but do not worry if this falls back in summer while the ventilators are open. This can be remedied by damping the floor in the early evening.
Cool-growing Oncidium orchids are mainly from the high Andes need a minimum night temperature of 11°C (52°F). This should rise in the daytime by 5°C (10°F) in autumn and winter; and by 10°C (20°F) during spring and summer. Temperatures a little outside these extremes can be tolerated.
Ventilation should be used from March to September. Oncidiums love fresh, airy conditions and it is a good idea to install a circulating fan, running all the time.
Each of the newly matured pseudo-bulbs flower, but usually only once. As new pseudo-bulbs reach a sufficient size and maturity they flower. This could be at any time of the year.
Repotting is best carried out from February to April or late August to early October. The exact timing will depend on the young shoot being between 2.5-7.5cm (2-3in) in height.
Instead of re-potting into a larger pot, overcrowded plants can be divided and the divisions potted up separately. However, Oncidium resents frequent root disturbance, so this should not be carried out too often. See the advice in orchids: indoor cultivation for more information.
Some orchids sold as oncidiums (syn. Odontoglossum) are in fact complex hybrids. The following are freely available from specialist orchid nurseries and can be recommended for cool greenhouse culture:
- Aliceara 'Peggy Ruth Carpenter'
- Oncidesa 'Sweet Sugar' (fragrant)
- Oncidium 'Ardentissimum'
- Oncidium 'Twinkle' (fragrant)
- Oncidium 'Wildcat'
- Oncidopsis 'Nelly Isler' (fragrant)
- Oncostele 'Wildcat'
For those wishing to try species be it rather more challenging the following are extremely attractive:
- Oncidium alexandrae
- Oncidium cirrhosum
- Oncidium crispum
- Oncidium nobile
- Oncidium spectatissimum