While browsing at various orchid newsgroups I came across a post asking about how to bloom Renantheras. There are various like minded orchid enthusiasts who generously contributed and share their personal answers.One nice lady by the name of Nancy said "Epsom salts is (I think) magnesium sulfate. It's one of those trace minerals often missing from standard fertilizer mixtures. Magnesium supposedly performs two functions: it helps plants to tolerate higher levels of sun without burning (it's seasonally-growing tropicals like plumeria), and it also is said to strengthen the plant walls, so the foliage can support itself and stay upright, rather than sprawling.
Many people around here use it several times in the spring just as growth is beginning, not only on orchids, but other high-light and fast-growing plants.
In garden plants, you can work 1/4 cup or so into the soil around the plant; for liquid feeding, I think a tablespoon (15g) per gallon/4 liter is average. I'm
pretty sure you can add the epsom salt to your regular fertilizer mixture - you don't have to use it alone.You can use both as a root and foliage feeder.
Additionally, you can add it to your bath water for muscle aches, but it can harm metal plumbing, so be sure to flush the drain with clean water afterwards.
I do not believe it will help me to tolerate more sun..."
It is not easy to comment without seing the actual plant. Writing on why orchids don't bloom in general is easier than why Renantheras don't spike. This topic is quite a challenge for me. However I have determined to provide my share of cultural practice here. I am now gathering some pointers for easy reference. If I can get it ready, I shall post it in my next session.