Petrocosmea is a small genus of rosette plants from high altitudes in southern China. Most grow on mossy rock, often limestone, in shady areas, although some species grow in wet mossy forests.
Species adapted to higher altitudes are likely to require cooler temperatures. Those growing above 2300m include P. duclouxii, P. flaccida, P. forrestii, P. nervosa, and P. oblata. P. flaccida and P. oblata are found above 3000m, and probably are adapted to light frost. Although rainfall may be infrequent seasonally at high elevations, plants probably experience regular fog/mist.
Plants recorded from lower levels include P. grandiflora, P. kerrii, P. parryorum (in wet mossy forest) and P. peltata. Bear in mind that there may be significant variation in the heights at which species grow. P. peltata and P. parryorum may be the best adapted to lower and warmer temperatures.
Growers report success with different strategies. Some growers (e.g. Marilyn Allen, see a plant here) grow Petrocosmea with other gesneriads under artificial light, often under fairly low light conditions. Marilyn reports good success in both warm and cool conditions, although P. kerrii and P. parryorum do best for her in natural light. As is appropriate, given the natural habit of growing on limestone rocks, Marilyn adds ground limestone to her potting mix for the Petrocosmeas.
On the other hand, others (e.g. Ray Drew, see a plant here) treat these species as tender alpines, allowing them to experience quite cool and dry winters, before encouraging a flush of growth and bloom in the spring. They can be grown in a frost-free alpine house with other tender alpines, planted in very sharply drained potting medium. A degree or two of frost may be tolerated. This treatment can result in a spectacular seasonal flush of bloom.
