Hmm, never heard of that. Sounds unsafe to me though, at least for tropical epiphytes. Salts generally need to be flushed out of the pots with low ppm water ('parts per million' which is the measurement of dissolved minerals in water). I'd stick with a good epiphytic fertilizer, or even any balanced general fertilizer as long as you dilute it quite as bit. Hoyas are kinda heavy feeders though. I use an all purpose seaweed based fertilizer called Maxsea 16-16-16. I use it for all of my succulents, orchids, airplants, and carnivorous plants. Basically everything. Hahaha

On a side note, for those who have experience, has anyone tried the coffee grind fertilizer? For asian pitcher plants (nepenthes), some growers swear by it, so I would think hoya can, and will appreciate similar techniques.

Magnesium is leached very quickly from the soil particularly in high rainfall areas, so deficiencies often show up. I sprinkle Epsom Salts in the garden and you can see the benefit with some plants, but not all. Many show no difference. But I never use it in pots, there's very little soil in them to act as a buffer. Mostly for Hoyas I use Blood'nBone or aged poultry manure. I remember Carol Noel (Aloha Hoya) always recommended poultry manure. But I also use the water from washing meat (which has some blood in it) and the Hoya rupicola especially likes that.

It has benefits on plants that are experiencing "wash-out" from too much sun, or just a general yellowing of leaves that is not associated with over or under watering. Other than that, I wouldn't bother with it. The coffee grounds routine, however, has proven quite beneficial. I have a friend who uses them in her succulents and many are flowering magnificently, so I plan to try it with my Hoyas.

Denise in Omaha

Ooo, I'll be trying out the coffee grounds!..I remember Mr Roper on Three's Company, he would use coffe grounds on his roses lol it worked ;-P the soil I use has guano and poultry manure. Hoyas seem to like it...the coffee grounds is a great idea. Always some around ☕