Oncidium orchids (cool growing)

Cool growing oncidiums produce exotic flowers of various colours, including white, pink and reddish-purple, often with darker spots or blotches. The small flowers are held on tall stems above clumps of long, narrow leaves that sprout from large swollen ‘pseudobulbs’ at the base.

These oncidiums grow best in bright but filtered light, such as near a north- or north-east facing window. They need high humidity and cool temperatures of 16–21°C (60–70°F), with a drop of up to 10°C (20°F) at night. Grow them in pots of bark-based orchid compost.

As their name implies, cool growing oncidiums don’t like to be too warm (ideally not above 21°C/70°F in summer), but also not too cold, so at least 11°C (20°F) in winter. They dislike low light and dry air. Overwatering and damp compost can cause rotting, so let them dry out between waterings, especially in winter.

This group of orchids used to be known botanically as Odontoglossum (tiger orchids), but have been reclassified as Oncidium. However, they like cooler growing conditions than traditional oncidiums, hence the name ‘cool growing’ oncidiums (while traditional oncidiums are now ‘warm growing’) – this helps to distinguish between the two groups, so you can provide the right growing conditions.