Cereus peruvianus "Monstrosus," commonly known as the monstrose apple cactus, is a grey-blue cactus with a branching, treelike form. This slow-growing cactus even produces fruit similar to dragon fruit when mature.
Cereus peruvianus is a large, erect, thorny columnar cactus up to 9m (30 feet) tall when growing in the wild. Though less gigantic in pots, they are much admired for their sculptural, columnar shape, which contrasts impressively with that of most other plants in any collection of cacti. Cereus peruvianus is native from rocky outcrops and the savanna in South America. Cereus peruvianus flowers in summer and opens at night time. Each flower blooms only one night and then dies. The flowers are followed by red fruits 2.5-5cm (1-2 inch) in diameter.
During the active growth period water moderately, but allow the top centimetre (0.4 inch) or so of the mixture to dry out before watering again. During the winter rest period give Cereus peruvianus just enough water to prevent the mixture from drying out.
Grow Cereus peruvianus cacti in the fullest possible sunlight. Since the light coming from a window is one-sided, a columnar plant will tend to lean in that direction and so it is most important to turn such plant frequently. If possible, get the Cereus peruvianus outdoors during the summer months for fresh air and extra light to improve their colour and to help lengthen their spines.
Either a peat based or soil based mixture will do well. For better drainage add one part coarse sand to two parts of the basic mixture. Plants up to 5cm (2 inch) wide may be kept in 8cm (3 inch) pots, but these cacti are fast growing and may need to be moved into a larger pots at least once a year.
At the beginning of the growth period apply a dressing of slow release fertiliser and stir it into the surface of the soil in the pot. Alternativelly, this fertiliser may be incorporated in potting mixture when repotting.
Normally warm temperatures are usually suitable in spring, summer and autumn. For the winter these plants should be moved into a cool position – around 10°C (10°F), if possible – where they can rest. A Cereus peruvianus that tries to continue growing in poor light of the short-day months will develop an abnormally thin, frail stem.
