I put up the clear plastic that is taped on and then tightened with a blow dryer on all my windows that have houseplants here in zone 5 (tape it directly to the shelf if I can't get it around). On truly cold nights I do close the curtain behind the plants. The plastic has definately helped. I have covered double 8 foot sliding doors with it. Not sure if your window area is too big for this.

This tho is the first year I am trying hoyas directly in a window with the plastic so I don't know if it's enough for hoyas???

Some Hoyas like it cool anyways, species like shephardii, serpens, carnosa and relatives, longifolia and linearis come to mind. Other warm growers will be fine down to 10 degrees Celsius but make sure their leaves do not touch the glass. The hot growing species will be better off farthest from the window or they may stop growth. If the window gets good light otherwise it is still the best place for your plants especially if they have been there all summer. I use a fan the moves the air around so that cold or hot pockets of air don't form around the plants. You might want to consider a fan in the room to keep the air from stratifying.

Mike

My hoyas live out side most of the year but if the temp goes down to 40 degrees F. I bring them inside. Most experts said not below 50 degrees F. but I tend to push a little.

Jan

Well maybe I should bring them away for the winter - move them closer in the house. I DO NOT want to push it. Cause for me to get these hoyas again might be difficult. We dont just sell them in the stores here in Canada - except for a carnosa. So thanks for all your help and helping me make a decision to move them to a warmer spot. I will put my stephanotis there - and I will look forward to lots of flowers on that next year!

Golden I think the main thing is to be sure that the plants have a chance to warm up during the day. Cool at night is OK but cool all the time is not such a good idea.

Good luck with your plants this winter.

Mike

Thanks Mike, Well the problem is I am Not Quite sure exactly how cold it does get in there? Its basically a box window in my kitchen and I close the blinds on them and it probably gets colder? As the heat from the house wouldnt get in there as much = and because its a window - it doesnt have any insulation - obviously. so I'm just scared I would kill them - so I thought it would probably be safer for me to move them to a warmer spot in the house during the winter. If I killed my stehpanotis - I can always get another one. The hoyas not so easy.