Indoor orchids are mainly epiphytic (growing on trees) or lithophytic (growing on rocks). In their natural habitat this means using trees or rocks as a support and feeding from plant debris accumulated around their roots. There are some terrestrial species that grow in the ground.
Many epiphytic and lithophytic orchids can be grown in containers filled with open, free draining specialist orchid compost. They often form aerial roots outside of the container.
Re-pot only when the roots have filled the pot, using a container that is only one or two sizes larger. Do not try to bury the aerial roots in the compost, as they may rot.
Temperature and light
Orchids like a variety of temperatures, so choose the best position in the house to suit the needs of the particular orchid you are growing.
Cool-growing orchids such as Brassia, Cymbidium, Dendrobium and Oncidium (cool) need a minimum winter night temperature of 10°C (50°F). A porch, heated conservatory or unheated indoor room would be ideal. If grown in warmer environment, their flowering is often reduced. They can be placed outdoors in summer in a shady position.
Intermediate temperature orchids such as Cattleya, Oncidium (warm) and Paphiopedilum prefer a minimum temperature of 13-15°C (55-60°F).
Warm-growing orchids such as the ever popular Phalaenopsis enjoy rooms indoor conditions all year round, with a minimum temperature requirement of 18°C (65°F).
Orchids generally prefer bright but filtered light. They need protection from direct sunshine.
Watering, humidity and feeding
Orchids prefer high air humidity, but their roots will rot easily in wet compost. Water them about once a week, ideally using tepid rainwater. Water from above and tip out any water that collects in the saucer under the pot. Alternatively, plunge the container into a bucket of water and allow to drain thoroughly.
Mist the foliage and aerial roots daily, or stand the pot on a wide saucer filled with gravel, filling the saucer with water to just below the surface of the gravel.
Reduce humidity in winter if temperatures are lower (this applies to orchids grown in porches or conservatories rather than those grown indoors, where temperatures are constant or may even rise in winter with central heating).
Many orchids need a rest period, usually during the winter months, when watering and feeding should be reduced.
Feed about every three weeks, with a proprietary liquid orchid fertiliser mixed into the irrigation water, from spring to autumn. Reduce or withdraw feeding in winter.
Propagation from seed requires specialist laboratory equipment, but some orchids can be successfully propagated at home by other means:
From plantlets: These appear from the growing points of stems of some Dendrobium, Epidendrum and Phalaenopsis species. Detach the plantlets when they have developed several good roots, and pot them up in orchid compost. Water them sparingly at first, and mist daily.
From stem cuttings: These can be taken from many Dendrobium orchids. Cut off a stem up to 30cm (1ft) long and cut it up into 7-10cm (3-4in) sections, with at least one dormant bud on each section. Place the cuttings in a tray of damp sphagnum moss, and keep them humid and shaded. Detach and pot up the plantlets that form from the buds.
By division: This method can be used to propagate orchids such as Cattleya, Cymbidium and Oncidium in spring, just after flowering. Only divide plants that are overcrowded in the pot. Cut through the rhizomes that join the pseudobulbs, making sure that each division has at least three healthy pseudobulbs. Trim off any dead roots and remove any brown and shrivelled pseudobulbs before re-potting the divisions individually.
Common cultivation problems include:
- Overwatering: Roots become soft and soggy. Root death causes collapse of the plant
- Overfeeding: This causes root damage. In severe cases roots and compost are covered with fertiliser crystals. Plunge the pot in water to dissolve the excess fertiliser. Do not exceed recommended application rates and do not feed during the resting period
- Sun scorch: This results in bleached, scorched leaves. Provide shade from direct sunshine
- Failure to flower: May suggest the need for a rest period, and/or a lower temperature period to initiate flowering
Orchids can suffer from aphid, scale insect, whitefly, red spider mite and mealybug attack. If kept outdoors during the summer, protect them from slug and snail damage.
Orchids can be affected by various viruses. The symptoms include pale green to yellow spots, streaks or patterns of brown, black rings and other patterns of discolouration. There is no cure and affected plants should be destroyed.