When I brought mine in for the winter, especially the Royal Flush, the leaves began to yellow and drop off. Eventually, I took it out to the greenhouse where it is thriving. My first thought is that the air in the house is very dry after being outside for the summer.
I'm sure other more experienced growers will offer more expert advice soon.
Beverly

We really can't say, esp. w/out seeing pix. I'm inclined to think it's a drainage problem, esp. since you haven't changed the mix in years.

If it were mine, I'd stop the fertilizer & the bottom heat, but then I'd also turn it out to check the roots; it's really the only way to be sure.

Have you cut down on watering because the potting mix was remaining wet for too long? Hoya pubicalyx is quite resistant to dryness but you don't want it to be dry for too long. If light levels are still good you should be watering as per the rest of the year and a slightly weaker fertilizer is fine as well. The bottom heat will speed up drying so watch closely.

I have several Hoyas that always seem to drop leaves in winter and I think it is just due to the change in growing conditions.

Mike

thanks for all the info. all of you here on this forum are so knowledgeable! i think that the drainage is fine, as you can see by the photos, it is actively growing. in general, taken as a whole, the entire plant looks in good shape, but it has lost dozens of mature leaves (no kidding!) since coming indoors for the winter. i definitely will repot this spring, but it will take the help of a couple of strong men in order to tip it out of it's pot! i hope the photos appear ok, i am new at this. if they don't i will try again. thanks cathy

Here is a link that might be useful: hoyas

Your plant does look nice and healthy so I am sure it will be just fine. I find that the leaves that tend to drop on my plant are the ones that formed when it was in very bright light. These light green leaves seem to be the ones that drop when the gloomy days of winter come around.
I bet your plant just explodes with new growth after being repotted. I repotted a well overdue Hoya carnosa a few years ago and it grew tremendously and bloomed very well come the fall.

Your photos did show up but if you would like to post them directly in the message you can copy and paste the html code right where you want the photo to appear. If you click the share button above your photo in Flickr you will find the html code. You can right click and then copy and then right click again and paste the photo into the message here on Gardenweb.

Mike