Not all cacti grow in deserts, many grow in forests clinging to trees. Plants that grow on other plants are called epiphytes and live on whatever light and water filters through the tree canopy, obtaining nutrients from the air and rain. Epiphytes often make effective houseplants including many orchids, bromeliads such as Spanish moss, certain ferns and forest cacti.
Christmas cactus from Brazilian forests is the most widely grown forest cactus for its mauve, pink, red and white winter flowers and graceful foliage. It is produced by commercial nurseries on a vast scale as a short-term houseplant, although many gardeners keep them going for as much as 20 years. Christmas cacti arose from a hybrid bred in England in the late 1840s, Schlumbergera × buckleyi, but modern ones sold as houseplants have a complex parentage, and are often labelled Schlumbergera truncata. They flower in the short days (8-10 hours) of November to January with cooler temperatures, particularly at night.
Commercial growers manipulate temperatures and also day length by illuminating the crop with nocturnal lights rich in red wavelengths. This fools plants into thinking the winter days are long, delaying flowering. The aim is to have flowers ready at just the right time for the lively Christmas trade, as left to their own devices they might flower in November.
Buy plants in bud as open flowers can fall off if the plant is moved, and avoid leaving them in a cold car as this too can dislodge flowers and buds. Choose plants that have not been left on pavements or other stressful environments.
Being forest plants they like dappled shade rather than strong light, an east facing windowsill, in a coolish room (18-20°C) is ideal. Keep the potting compost moist and never soggy.
After Christmas, rest them by keeping slightly on the dry side and cooler (12-15°C ideally) until late March. The resting period is important for all forest cacti. Rest them again in autumn from mid-September until the buds appear, again at 12-15°C, but certainly less than 20°C or flower buds won’t form. Water more through the flowering period. They appreciate a summer outside.
Other houseplant forest cacti include Easter or Whitsun cactus (Hatiora gaertneri) from Brazil. Here the cool rest period is mid-September to January until buds form, after which more water can be given until they flower in April/May when they need warmer conditions; 20°C+. A summer outside until mid-September is ideal, but these cacti are fussier than Christmas cactus.
Fishbone or zig-zag cactus (Epiphyllum anguliger) named and grown for its deeply notched leaves that vaguely resemble a fish skeleton, comes from Mexican forests. It flowers in summer. Other Epiphyllum are grown for their spectacular early summer flowers. Here, their cold (10°C) rest period is December to February with water and warmth increased once flower buds are visible in April or May with similar conditions post-flowering until their rest period.
All forest cacti look good in hanging baskets but Rhipsalis are notably trailing – an example is the hairy wickerware cactus from Brazil, Rhipsalis pilocarpa, with trailing hairy stems. Since flowers are of secondary importance they are just kept warm and in filtered light.
Forest cacti need little repotting, perhaps once every three years. They prefer reasonable humidity so avoid long periods in hot dry centrally-heated rooms. Monthly feeding when they are not resting will build plants up.
Cuttings of their long stems root readily, and by taking cuttings more stems and therefore flowers are promoted. Flowers form on stem tips.
