Epiphyllum are one of the classic epiphytes, that is plants that grow or perch on other plants and get most of their nourishment from the air. They are never parasites
but use the other plant such as a tree, or pole, roof gutter, etc. as a perch in order to gain more sunlight and moisture. Most are (sub) tropical species.
Epiphyllums originate in the tropical Americas from Mexico through Brazil. Today their progeny have spread throughout the world's (sub)tropcial zones and are also widely grown as glasshouse and indoor plant specimens in cooler climates. There are four main species and at least 50 hybrids.
All have spectacular blooms many reminiscent of a large water lily in a wide range of colours other than true blue. The word Epiphyllum is Latin for 'on a leaf' in allusion to their unusual habit of one leaf emerging from the side of another and flower buds emerging in a similar way. These are true cacti but usually spineless or with soft cacti hairs protecting only delicate tissues of newly emerging shoots.
But unlike other cacti Epiphyllums are not desert dwellers but more often habitat tropical rain forests and warm, moist climates where they often perch in the mossy, humus-rich crotches high up in the forest canopy. For this reason Epiphyllums enjoy a richer somewhat peaty soil mix and more water than most other cacti. They are not particular about their growing containers and will usually do as well in terracotta as in plastic pots and their epiphytic background makes them ideal subjects for larger hanging baskets.
As to watering,clay pots and baskets tend to dry out a little faster but work as well as plastic containers. The Epiphyllums natural growth cycles dictate the amount of water required. They commence new growth as soon as sunlight and warmth return in the spring, producing buds and flowers usually from high spring through summer and sometimes into the autumn with new growth obvious
throughout these warm months. The plants demand more water during this time. But this should be given only during warm, sunny conditions otherwise the plants can chill or rot. Unless strongly artificially heated Epiphyllums usually rest after flowering and again during the winter months.
If an Epiphyllum begins to look wilted it may mean that it's roots have chilled from too cold a position over winter, or dried out too severely from lack of water and sometimes this can result from the stress of producing flowers. Unless the plant is obviously bone dry, do not radically increase the amount of water that you have been giving them. This is often a natural phenomenon and the plants will usually recover. If the soil is moist but wilting continues, the roots may have rotted, in which case the entire plant may lift away from the soil. Simply place the plant back into fresh potting soil and find a warmer, sunnier place for it to grow.
During the winter months, give the plants just enough water to stay moist. The main thing to remember about watering established Epiphyllum (Orchid Cacti) is that the mix should never be allowed to dry out completely nor ever remain wet during cold, cloudy weather. Throughout the warmer growing season, usually it is best to give them a thorough soaking so that the water flows freely from the drain holes and then not water again until the soil has nearly dried out. Many growers allow the top 1/3 of the mix to dry before watering again, using their finger to determine when this has happened. It is best to check the mix every few days to see whether it is time to water.
Being natural tree-perching plants, Epiphyllum prefer strong filtered sunlight or a few hours of morning or afternoon sun. In cool climates the plants may be grown under glass, or near a window receiving strong morning or afternoon sunshine. In frost-free climates they are ideal for a lathe or shade house or underneath the dappled shade of a spreading tree. In most climates they benefit from a summer holiday in a warm and sheltered spot outdoors.
Epiphyllums prefer moderate temperatures that range between 45-70 F (7-30C) degrees. They will tolerate more extreme heat provided they are kept well shaded, moist and humid. Epiphyllums should be protected from frost and freezing. They will tolerate lower temperatures during their winter dormancy period provided their soil remains rather dry but will only withstand temperatures of less then 32 degrees for a few hours before they chill and collapse. The small flowered hybrid Epiphyllums such as zygocactus and nopalxochia are particularly susceptible to cold damage.
Being natives to (sub)tropical regions most Epiphyllums prefer sunny but cool winter temperatures and the slightly longer nights are necessary for proper bud formation. Being 'air' plants, Epiphyllums enjoy good air movement with plenty of space for air flow between plants. Avoid deep over-shading and overcrowding, hot seering winds and especially chilling drafts which often result in fungal attack or root rot that can quickly kill the plant.
Epiphyllums are fertlized at least once a month from spring through autumn and allowed to rest throughout the winter.They respond well to both liquid, foliar and granular type fertilisers. From spring through summer most growers choose a balanced fertilser such as 10-10-10 but avoid high nitrogen fertilisers especially early in the season else leaves will be produced at the expense of flowering. After flowering or from late summer onward use a fertiliser higher in phosphorous and potassium and low in nitrogen such as (0-10-10, 5-15-45, etc which will promote budding and harden off tender young growth in time for winter.
Epiphyllums suffer from few pests and diseases. The most common pests are Scale (small round tan/white coloured insects) and Mealybug (white fluffy insects that leave a cotton like residue), both of which can be easily controlled with any number of insecticidal sprays or a home-made solution of spraying oil mixed with soapy water. Baiting for snails and slugs may be necessary as both snails and slugs love Epiphyllums and are particularly damaging to new emerging growth.
Fungal attack and root or crown rot can sometimes cause dark brown or black spots or holes to develop and spread on leaves and branches. If left uncontrolled this can eventually result in wilting foliage or plant collapse. The secret is moderate watering, good ventilation that allows the plants to dry out combined with constant mild temperatures that are not too high during the day or cool rapidly in the evening providing as close as possible to a perfectly controlled environment.