Although being a sub tropical palm Rhapis excelsa adapt very well to many environments, as long as time is allowed for gradual acclimatization.
The optimum growing temperature range being 20C (68F) - 23C (73F), which makes them ideal house plants, also tolerating dry indoor conditions.
During the winter it is probably best to keep the palms on the cool side for a time as this will harden them. Too high a temperature in the winter could weaken the palms and produce leggy growth. 10C (50F) - 15C (60f) seems about right and the palms will continue to grow slowly. The palms will stop growing below 10C (50f) and will survive even down to freezing if protected from frost.
One reason Rhapis palms make ideal house plants is their liking for low light interiors. Rhapis palms will survive in very low light but if they are to grow well they do need some filtered sunlight to thrive and produce new offshoots.
When you first get the palm you need to know what conditions it had been used to so that you can gradually get the palm used to its new surroundings.
If the palm is grown in quite bright light the green leaves might have a yellowish appearance which can been compensated for by giving extra fertilizer, being careful not to over do it. Great care must be taken with delicate striped leaves as they can easily be scorched by strong sunlight.
More house plants must have been killed from over watering than any other reason. Rhapis palms like to be moist but not wet and soggy. An indication of when to water would be when the surface of the compost is some what dry.
Also get used to the weight of the pot before you water.
A plastic pot would require less watering than a clay pot and a clay pot less watering than a Kannonchiku pot . The Kannonchiku pot is very porous with a large drainage hole, so the pot dries out quicker and can be watered more frequently giving more oxygen and moisture to the palm.
A good method of watering would be by immersion in a bucket. Immerse the pot twice and drain off this will also have the effect of leaching out any deposits of salts from fertilizing. Do not let the pot stand in water as this could cause the roots to rot. If using a plastic or clay pot stand it on dry coarse gravel to help air circulation under the pot. This is not necessary with a Kannonchiku pot as it has three feet to stand on.
fertilizing
As Rhapis palms grow so slowly they require very little fertilizer, but to look their best and produce new offshoots they do need to be fed sparingly. Also different cultivars require different amounts of fertilizer so if you are not sure ere on the side of caution As a general rule when feeding liquid fertilizer use half the amount stated for green cultivars and one quarter the amount for variegated cultivars.
Another method of fertilizing can be used in conjunction with or instead of liquid feed is 'place' fertilizer , the Japanese term is Okihi, and is a slow release organic fertilizer . It is made by mixing cottonseed meal as the base 60%, powdered fish 20% and powdered bone 20%. To this mixture add a little water , mix again and leave to ferment in a sealed container for two to three weeks.
After fermenting form the paste into 1-2 cm balls and leave to dry hard. One or two of these can be placed around the soil surface in the pot so that when the palm is watered a little of the fertilizer is washed into the pot.
There is room for experimenting with different mixtures but be careful with delicate variegated palms as if too much fertilizer is washed into the soil the roots can be scorched. As a way of making the balls of fertilizer harder so that less is washed into the soil, I added two egg yolks to the fermented mixture!
soil
Rhapis palms prefer well drained soil with a ph of around six, a soil suitable for 'African Violets' is fine. Or use: - Four parts ericaceous peat based compost, two parts perlite, one part vermiculite, two parts coarse grit with plenty of bean size gravel for drainage.
The Japanese method is to use three grades of sand/gravel , large (bean size), medium (pea size )and small (rice size). This results in an extremely free draining mixture which requires very frequent watering, but dependent on where you live could be the ideal soil for achieving the palms full potential. So if your climate is not too hot and you have good water this could be the best method.
pests and diseases
Rhapis excelsa grown in the United Kingdom and given the correct cultural conditions are affected by very few pests and diseases.
However 'prevention is better than cure' . So regular monthly spraying with pesticide and fungicide will go a long way to prevent any attack.
Scale insect is something to look out for especially when new leaves are emerging, look for any woolly deposits in the leaf joints. If you find a scale insect pick it off and spray immediately.
Brown spot is a fungal disease and can effect especially the older leaves with brown spots and blemishes, it could be caused by cold and damp conditions.
Any infected leaves should be removed to avoid the infection spreading to other palms.
Rotting roots can be a problem, not a disease but caused by bad cultural practice, over watering and fertilizing. The leaf tips will turn black or reddish brown. The palm should be removed from the pot and the roots checked, any blackened roots shoud be removed, wash roots in fungicide and repot.
The leaves of delicate variegated palms can be damaged by too strong sunlight, and scorched by drips of water left on the leaves in the sun. Keep well shaded.