Nepenthes Rajah Cultivation
Nepenthes rajah is an ultrahighland mountain plant which is a challenge to grow. It is a medium slow grower. Failing to keep its ultrahighland requirements continuously will result in the eventual demise of the plant.
Cultivating Ease - Challenge. Much easier for growers who live where the nighttime temperatures fall into the 50's in the summer. Larger plants with a well established root system are much easier than small plants with little to no roots.
Type - This plant is an ultrahighlander. It grows in high elevations where the night time temperatures drop considerably.
Temperature - Keeping the temperatures in the mid 80's with a night time drop into the 50's is needed. Keeping the daytime temps out of the 90's is necessary, especially if this causes the humidity to significantly drop. Daytime temperatures should ideally be restricted to the mid 70's to mid 80s. If grown in a greenhouse, it should be placed next to the swamp cooler.
Humidity - The daytime humidity level should be kept above 70%. The nighttime humidity should be very high.
Light - I keep my plants in bright light, but out of direct sunlight. (An update to this is that I have also grown the plants in direct sunlight, in which they did quite well.)
Moisture - Keep the plant moist to wet. Do not let the soil dry out, as this can cause the roots to heat up. The plant should be constantly misted. In the wild, the plants grow in slightly open areas which are slightly depressed and in which are kept very wet.
Soil - Long Fiber Sphagnum
Size - This plant is a slow growing scrambler. It will grow well for years in a cooled chamber. In a greenhouse, it should be grown near the swamp coolers. It also appreciates mounds of overly waterlogged sphagnum being kept around the plant (not the soil the plant is growing in, which should not be waterlogged). Misting this soil with cool water helps. But the plant will eventually grow to a decent size, producing very large pitchers, only possibly surpassed by N. truncata, N. merrilliana, and a few hybrids. But this plant probably produces the largest lid of any Nepenthes trap, being extremely large and vaulted.
Details: This is not a beginners plant. It is very unforgiving if the daytime temps soar, if the daytime humidity fluctuates below 50%, or if the night time temperatures do not drop significantly. Its ultrahighland conditions must be kept up constantly, especially for small plants with no roots or an underdeveloped root system. Larger plants are much easier than smaller plants. If you purchase smaller plants, they should have been growing in greenhouse conditions for at least a year before attempting to purchase them.
N. rajah's tendrils on plants larger than 4" in diameter or so will drop off the leaf about an inch or two from the end of the leaf. The only other plant I can think of that produces this marked of a tendril to leaf termination is N. clipeata, although many species of Nepenthes can do this to a smaller degree. Smaller N. rajah plants do not necessarily produce this phenomenon until they reach about 4" in diameter. Larger Nepenthes of many species may drop the tendril slightly off the tip of the leaf, but none are as exaggerated as N. rajah and N. clipeata.
Propagation - I have not attempted to propagate this plant yet.
Forms - Only the typical form has been mentioned.