The deep emerald green leaf colour tells me that your plant needs more light, it will not bloom with leaves that dark. If you can get the leaves to be a medium green I am sure you will see flowers. Light green is not bad either but it does mean that your plant is stressed. You most likely have a Hoya carnosa or pubicalyx from the description of the leaves.

The best mix to use for Hoyas is one that is open, added perlite, diatomite, orchid bark, or coconut husk chips will open the soil mix up and make for a better root system. You need to focus on getting the plant's root system into health and then the plant will begin to recover. The old light green leaves will most likely not regain their colour so you might have to trim back the old growth once things improve. You could also start a new plant from cuttings but if there are not any really healthy portions of plant left you may as well focus on getting some new roots to form on the old plant.

Can you tell us how big the pot is in relation to the root ball? You want a fairly small pot and a good open mix. A large Hoya can grow in a small pot, large pots just cause problems.

Here is a photo of one of my plants in a 5" pot. Smaller pots allow the mix to dry out before you water again and this is what many Hoyas want, constant dampness is not well tolerated and when a mix degrades problems can start and root loss is the result.

Mike

Mike has given some great advice.

If I may add, sand is a terrible ingredient for soil mixes. Sand is entirely too fine,
and the small particulate not only compacts upon itself but it also lodges between larger
particles and impedes drainage. In addition, a layer of stones or gravel at the bottom of
the pot actually blocks drainage, and creates what is called a 'perched water layer' in
the soil immediately above the gravel, where water comes to a stop and then travels laterally
before slowly exiting the container. This layer remains saturated for long periods of time
and roots will die and then rot in such an environment.

When you say that you water every 4 - 6 weeks, I know that the soil is holding too much moisture.
Your plants will be so much healthier if they are re-potted in a mix that allows you to water them
thoroughly and frequently without fear of root-rot.

So I recommend that you tip the plant out of its pot and, at the very least, remove the gravel.

Josh

A plant that size should have a good size rootball, so it sounds like root issues. And I water mine much more often. Like Josh says, you need a pourous mix so you can water often and it dries out fairly fast. Mine is simple - 2/3 coir and 1/3 perlite. And you need to use fertilizer every watering at about 1/4 to 1/2 strength - just a multi-purpose fertilizer in winter at 1/4, and a bloom booster in spring/summer at 1/2 strength. Sounds like your light is about right.

Denise in Omaha

I found a picture online of mine! You're right, it's a Hoya pubicalyx. Hope they don't mind me posting the link here: http://khedlund.tripod.com/hoyapdl/pubi.html

I will say that since repotting, even in the wrong soil mixture, Madame Hoya has been very busy growing new leaves and new shoots all over the place. I hope this means that perhaps with some tweaking of the potting medium that she will be happy enough to break out some blooms for me. The new leaves start out bergundy, extremely glossy, and as they mature they become a rich emerald with these gorgeous silver-white splotches on them. She's getting 3-6 hours of direct sunlight, so I'm not sure how it's possible to get more direct light on her. We don't have a big enough south facing window. My plant is very large! So next best thing we have is putting her inside the east-facing bay window, right next to my orchids who bloom rather abundantly even with the direct sunlight (supposedly they don't like direct sun - somebody forgot to tell my orchids this fact).

Thank you very much for the tips - - I will definitely go to the store this weekend and pick up some orchid mix and re-pot her in that. Keeping my fingers crossed that this will result in some flowers!

Just learned that my great-aunt has potted up a Hoya Compacta for me so I'm pretty excited about that. Her plant is just beautiful.

Cheers and all the best for New Years!