Hi, Sorry to hear of your trouble. I'd turn out the worst looking one & check the root condition & the drainage. If you grow Hoyas, you've probably heard that yellowing can be from over or underwatering.

Can you explain your mix pls.? Looks like you've got Leca stones mixed in w/ your mix, not sure how the drainage would be in that, a bit confusing to me.

Hoyas don't necessarily go dormant just because we are growing them in cool parts of the country. Unless you are growing a species that likes a dryer winter rest then you should try to keep the light and temperatures as close to summer as possible. The move indoors in the fall, or even for plants that I grow in the same spot indoors all year always means a few yellow leaves for my Hoyas.
Make sure that plants are not too dry but also species that like to stay moist should be watched for dryness. Once the heat is in indoors some plants can dry out very quickly so keep an eye on them.

Can you tell us the Hoyas you are having problems with and then perhaps we can decide what the problems might be. What are the night time lows inside as well as the daytime high temperatures?
As long as you have nice bright light and warm temps during the day you should not stop fertilizing. You can fertilize at 1/2 to 1/4 strength but there is no need to completely stop.
Do your plants seem to be taking much longer to begin to dry out? I would recommend using a different method to watering, no schedule but lift the pot and then decide if it's wet/heavy or light/dry. Watering say every Saturday will leave some plants too wet while others will be too dry.

As far as drainage goes I don't think you need to worry. If you are using clay pots you will notice that the potting mix dries very quickly. Are all of your Hoyas in clay? Are the plants that are dropping leaves in clay?

Mike

I agree with Mike that when fall and winter roll around a scattering of yellow leaves is to be expected regardless of the plants being put through any outdoor > indoor transition. I don't think your plants' condition looks too worrisome at the moment (except #4, which personally I'd intervene with immediately). As long as the watering schedule is as satisfying as it can be, they'll buck up and get over their temporary upset.

This year, I slowed down my watering dramatically the minute temperatures started to descend, even though we still had plenty of warm days for a while. I am letting my pots get very light before I water again. You can't go by schedule, but I am estimating I usually hit my plants closer to every 1.5-2 weeks. They are all getting fertilizer and most seem fairly active. I am seeing a lot fewer problems than the year before, but there are still some lost leaves. On the other hand, the subsection of Hoyas I have here at the office tend to be kept very moist and are pressed against a very cold window, and I haven't seen a single bit of yellow. I kind of feel like the ideal method for my residence and collection is to let them dry out well, but keep them above humidity trays. Most Hoyas will gracefully endure the imperfect watering we give them during seasonal change, if there is bonus humidity.

I definitely don't think your problem is too much light - that's almost impossible indoors, and typically you'll see obviously burnt or sun damaged leaves if you do have a more sensitive Hoya. Based purely on my own experiences, it feels most likely that your plants are getting too much water and staying wet too long. PG and Mike are both asking questions to get to the bottom of this, but my advice is err on the side of too dry. Most of the Hoyas in your pictures fall in this camp.

Sounds like a mix issue to me, too - and by that, I mean a root-zone issue.
Do as Pirate Girl suggests and check out the roots on at least one of the hoyas.

Josh

3 of the five plants affected are clay.

Here are some pics with names.

https://picasaweb.google.com/planbb/Hoya2?authuser=0amp;feat=directlink

Drainage is really good and so I think underwatering might be the issue. I adjusted the air vent a little over a week ago so they may have been getting too much air across them in combination with lack of water.

Mix
2/5 = Chunky Orchid Mix (Bark,charcoal, perlite)
2/5 = Leca balls (volcanic balls)
1/5 = potting mix

Air circulation is usually very good for them, so I doubt that was a problem. If they are very dry often, then yes, water. but if the soil feels at all damp...hold off in winter as they like to be dryer then. It may be your pots are too big for the smaller plants. Try looking at the roots and maybe potting down to smaller pots if you see very little good roots. I keep newly rooted cuttings in small pots for a very long time till they fill it up with roots.

Can you tell us the species involved? Some Hoyas do not want to dry out and will sulk while others like a dryer period each year. I do think the clay pots could be the issue because they are just not suitable for growing moisture loving plants unless you are very attentive to their watering needs. I have one Hoya in clay and that's because it's a large leafed species that likes it dry in the winter, otherwise clay is trouble in the heated indoor environment. If there is a heat vent blowing on the plants that is an issue as well because it will strip the moisture from the pots in no time flat. Plants do like air flow but if it is directed right at them there can be problems. It's best to keep the air in a room moving but not to have the plants directly in the air currant unless it's either nice and humid or the air flow is relatively weak.

Mike

I'm still confused about the Leca stones. I use them in my Hydro set-ups but not mixed into my mix. I haven't heard anyone doing this. Am wondering about the particle size of your 'potting soil', could it be very fine & peaty, thereby clogging things up a bit? I can't quite fathom the size combination of Leca stones & fine particles, sounds like that MIGHT be trouble.

I still suggest you unpot the worst looking one. That's really the only way to know for sure what's going on w/ the roots.