Light: Bright gentle light to dappled shade. Protect from direct afternoon sun to prevent leaf scorch.Temperature: Warmth-loving (65–90°F). Very sensitive to cold—protect from temps below 60°F.Humidity: High humidity (60–80%) is ideal. Absolutely thrives in a greenhouse or humid indoor environment.Water: Keep soil evenly moist during the growing season. Allow the top inch to dry slightly between waterings but never let it fully dry out.Potting mix: Rich, well-draining aroid mix—combine chunky bark, perlite, and peat or coco coir.Fertilizer: Feed monthly with a balanced, diluted fertilizer during active growth (spring through early fall). Cyrtosperma johnstonii is a tropical plant native to the Solomon Islands in Oceania. Similar to its huge siblings C. merkusii and C. giganteum, it also has large, starchy rhizomes and gigantic leaves. This plant is grown across Southeast Asia as an ornamental, and despite its popularity, not too much is known about its origins or ecology. I decided to write quite a detailed plant profile in an attempt to condense as much information about this species as possible, so bear with me, it might get a bit heavy. When young, its leaves have bright red veins, and as it grows older, it trades this colouration for sheer size. Its leaf blades or laminae can grow to over 1.5 metres in length, held up by towering, spiny pink and brown petioles. This descriptionsuggests a total height of 3 metres, but I would argue that I’ve seen plants taller than this in Singapore, with leaves over 1.5 metres long. This plant is variable in morphology and flowers at different sizes. I have seen small, stunted plants growing in full sun, holding onto their painted juvenile leaves whilst three metre tall plants unfurl gigantic, plain green leaves in dappled shade a few metres away. As previously mentioned, C. johnstonii is a very variable plant, despite the fact that most plants in cultivation are likely clones. Appearance varies with age and growing conditions. Plants usually grow in clumps with a dominant crown at the centre. They often produce suckers, although not as freely as C. merkusii. I’ve found this plant to be tolerant of most light conditions. In deep shade, plants lose their colouration more quickly and produce more spindly growth as one would expect. Light or dappled shade seems to suit the plant very well, and this is where I have seen the biggest specimens. The leaves of these plants are a deep green colour, which can make them harder to recognise. Plants grown in full sun tend to develop a more yellowish tinge to the leaf blades. For my plants, I’ve noticed that leaves produced in summer are a bit smaller and yellower in colour. At this time of year, the sun falls directly on the plants for a few hours per day. In winter, the plants only receive indirect light and produce bigger, greener leaves. There isn’t much, if any information on the habitat of C. johnstonii, but looking at the vast number of plants grown as marginals and bog plants it is safe to say that it loves water. I am also aware of plants being grown successfully under “normal” watering conditions in coconut chips. I let one of my plants dry out completely last week and it soon let me know, the whole plant wilted in a dramatic fashion and I was worried that I lost it. I soaked it in water and within a few hours it was back to normal. The roots didn’t show any damage, although I wouldn’t recommend putting it through that stress on a regular basis -Lost and Fern Blog (https://lostandferned.wordpress.com/2020/02/15/plant-profile-cyrtosperma-johnstonii/)
