Oncidium orchids are a wonderful addition to any collection, but do have slightly higher requirements than Phalaenopsis orchids. They are fussier and sometimes less forgiving than the Phalaenopsis but if you get their care right, they are absolutely worth the extra attention. My favourite orchid is in this genre and I don’t mind admitting, is on a bit of a pedestal.
Oncidium orchids tend to have a fragrance to them, some stronger than others. It does take a few days after the blooms open for the smell to start making itself known, but it is wonderful when it does.
So, how do I care for my Oncidium type orchids?
Oncidium orchids are sympodial orchids meaning that they produce new pseudo-bulbs in their growing season. Oncidium pseudo-bulbs take about 8-9 months to fully mature and produce blooms. This is the rule, but of course there are exceptions! Some orchids will bloom on immature growths, but that depends on the orchid.
Oncidium orchids are prone to developing accordion shaped leaves when the humidity is not high enough. As the leaves grow, they need moisture to help them remain straight. If there isn’t enough, they stick together but continue growing at the same time, causing a buckling effect. If the plant is producing a flower spike within the folds of a crinkled leaf, it will also crinkle. Increase the amount of humidity by misting more often or invest in a humidifier. All I have is a spray bottle and I mist twice a day in the summer, maybe three times, to keep the humidity above 55%. Any lower than this, and I find this buckling of the leaves becomes a problem.
You will see in stores that blooms are usually staked for support. Unless my orchids are so overloaded with the weight of a bloom spike, I do not use stakes. My reasoning is that this would not happen in their natural habitat, so it doesn’t happen in the grow space. It is perhaps more aesthetically pleasing to the eye to have the blooms following a stake but I just don’t like the look myself.
Most of my collection are intermediate growers which means they prefer temperatures of 18c – 24c. Whilst it is easier for me to maintain 18c or above, in the summer it can be tricky keeping temperatures below 24c. Having air movement helps to keep the leaves of the plant cool; a fan is useful, as is daily misting. This doesn’t always guarantee cooler temperatures, but the heat doesn’t last for weeks on end, so the orchids should cope with it.
Oncidium orchids will require air movement to help keep moulds and rots down, but also to promote overall health. My grow space is not that close to a window however there are patio doors which help with air flow, as does our trusty floor fan. I’ve only really had a problem with rotting or mould when air flow is low and moisture levels are high.
Most Oncidium orchids prefer to be kept moist and will not tolerate the media drying out completely. Oncidiums should be watered more frequently than Phalaenopsis; I tend to water mine twice a week in the summer, maybe more, but I drench them when I do. When the media is almost dry, then I will water them again.
Some sources suggest that you should only flush the pots through when watering. I personally disagree with this. I have an Oncidium Twinkle that does better when she is left to soak in water / fertiliser mixture for about 15 minutes once a week. If I just flushed her through, her pseudo-bulbs start to wrinkle and she doesn’t look as pretty as she could, because she is not getting enough water. Soaking her roots avoids this problem, but I do ensure that the pot is almost completely dried out before soaking again. If your orchid is showing signs of wrinkling bulbs even though you know it has a good root system, try soaking it to see if that makes a difference. The number of new growths the Twinkle created after I made this change was significant.
Oncidium orchids do not appear to me to be heavy feeders; the structures on the ones I have are smaller than Phalaenopsis and so do not require as many nutrients. This said, I still water them once every two weeks with growth or bloom fertiliser depending on what their requirements are at the time.
Oncidiums like to have media that will retain water for periods of time, but not so that it saturates the roots. I use bark chips for my Oncidiums, as it allows drainage whilst holding enough moisture to last for about 5-6 days. You could use a combination of bark chips and sphagnum moss to help retain a little more moisture, if you find bark doesn’t work as well for you on its own.
As the media needs to be kept moist, it is likely to break down quicker than with other types of orchid. The media should be changed every 2 years, or earlier if you notice a mushroom smell when you water your orchid. Inorganic media may work better from the point of view of providing moisture for longer periods of time, but I have not worked with it so cannot comment.
Container / Pots to use
There are no specific types of pot that would be better than others. Most of mine are in my favoured clear plastic pots to help me see the condition of the roots and the moisture levels of the media. The pot size should only increase when the orchid has created more pseudo-bulbs than the pot can comfortably contain. You’ll know when to repot it because the plant will look like it is beginning to crawl out of it! Wait for the new growths to produce roots before repotting; this way the new roots will not get upset by the change in media.
As most Oncidiums are intermediate growers, they should be placed somewhere that is relatively cool. They also do not like bright or direct sunlight so a shady spot is ideal (though they can cope with early morning or late afternoon sun – at least mine have).