65F should be fine for 99% of them. If you think they are too cold, decrease watering. Most orchids can take cold (colder than their ideal temp) but don't like cold AND wet.

I saw one cheap homemade greenhouse which occupied a low table. He cut the legs of an old table to lower it. Then made a rectangular hole in the middle to fit a 1/2' deep rectangular basin. Add water and an aquarium heater to keep the water at 80F. Plastic grid covers it so that space for plants is not lost. Numerous wooden stakes in orchid pots support a plastic sheet that covers the whole thing and hangs over the side. It traps warm air beautifully, his aquarium heater goes on and off and could keep it even warmer..

He has no lights as it sits in an outside sunroom which gets too cold but has lots of light. One could add lights under the plastic which would add heat. This contraption is big enough for 50 odd orchids, use the concept to build something smaller. Heat is provided by and aquarium heater or the lights. Problem with lights is that they tend to go off at night when it's the coldest so the heated water is the best way to go.

Nick

Just thought of something. My grandson has an iguana which enjoys the heat from a heat lamp which does not give off light so can be on all night. A couple of these should do wonders.

Nick

Join the local orchid society. The American Orchid Society has the list of local chapters. Orchid growers near you have created successful methods of managing your climate. And most growers like to talk about their methods. Good luck

Honestly, for the winter your temps are fine. Don't worry about it :)

Having grown for many years in NY, I found that leaky windows are worse than cold rooms. If you have your plants close to windows, check for leaks. Best case would be that your windows are newer and energy efficient.

We lived in a contemporary style house with large (old) windows and high ceilings. Very drafty and chilly. We kept the temps at about 65 at night but the temps near the windows got much colder. I moved the sensitive plants back from the windows and used floor lamps which gave some warmth.

My really sensitive plants went into a small spare room with octopus lamps and vaporizers going all night. They pulled through fine.

Most people have more energy efficient and better insulated homes than we did. Would cost us a small fortune to heat in winter.

I had a lot of plants. If you have a small collection, any of the above suggestions will work. Phals are sensitive to cool temps over a long period. The suggestion to keep your plants dry is the most important.

Jane

I have a radiator style heater that use at night during the winter. This year I am adding a seedling heating pad under some of mine that are real warmth lovers. I over winter in a back room which gets much much cooler than the rest of the house. In the dead of winter, day time temps are in the high 60s to low 70s, but night time can get into the 40s. The radiator heater brings the temps into the low-mid 50s. I am hoping the seedling pad will help with the special warmer growers.

To Nick's point, I water everything less in the winter to help them make it through the cooler temps.

I also agree that your orchids will be just fine with 65 degree temps.

Thanks for everyone's ideas. It's my first winter with 10 orchids, so I've been overly worried about their comfort. I will start watering them less and see how things go.

I want to join my local orchid society chapter, but their next meeting isnt until December. I know they'd have good advice, but I wanted advice a little sooner :)

I am glad you got the advice you need. I am a member of my local society and I still post here for advice. It is good to hear other's perspectives.

In the "sub Tropics" winter nights often get down to the 40 to 50F range and sometimes into the 30'F but the days always warm up. Maybe that is why some orchids that are easy to grow here and in parts of California are difficult in the frozen north.
I am not talking about caspar milktoast Phalaenopsis. I am talking about nobile type dens, Australian native dens, even Tolumnia etc. etc. Things that need a winter dip at night and where the days warm up.

The original post said 10 orchids to care for....Well there are easy orchids, difficult orchids, orchids from the tropical lowlands, orchids from tropical savannah, orchids from cloud forests and so on.
65F to 70F might be fine for some, others will need a simulation of the climate where the ancestors came from to do well. Nick can provide many of those conditions!
What we need here is someone to tell us some names of orchids that are tolerant and flower in a narrow indoor temperature range.

Do you know if all 10 of your orchids need Intermediate temperatures? If so, 65-70F should be fine.

Other indoor variables are light, RH (relative humidity), and air movement. Do you know what each of your orchids needs and if their winter location provides these? If all of them grow in Phal conditions, you're good.

As for temperatures, as Jane said, windows can leak cold air. Here in Minnesota, I cover the glass inside with 3M clear plastic film (no financial interest):

# Indoor 5-Window Insulator Kit
# Insulates five 3 x 5 ft. indoor windows
# 62 in. x 210 in. clear film
# 1/2 in. x 27.7 yd. tape
# Performs like an extra storm window
# Shrinks tight for clear-as-glass results
# Reduces condensation & stops cold drafts
# Helps reduce heating costs & save energy

Online, the Mills Fleet Farm price, for example, is $12.79. Other brands may be less expensive.

My orchids are in a bedroom. The 4' x 4' windows face E/SE, and putting film on them keeps the room warmer, keeps RH higher, and cuts down on the need for the little space heater. All winter, there's a fan going for air movement, and there's supplemental lighting from an LED and CFLs.

For a couple of years, I didn't get around to putting film on, and the orchids didn't do as well the rest of the year. In S. Carolina, the insulation may not be as critical.

Hope this helps, WhiteCat8

Here is a link that might be useful: Scotch Indoor 5-Window Insulator Kit

In fairness though, mine are in south facing windows for the winter where they get warmed up by the sun ( when it's out) and so they get that temperature change that they need most days. And getting a bit cooler at night (my house is set at 68, we just got new windows so the dip won't be too much) is fine. The cool growers just get put in a room that we don't use much so that they're a bit cooler all the time. I'm sure your babies will be fine. I have far more than 10 and they do fine over the winter.

I have around 100 orchids growing in my sun room that is heated to 65 at night and during the day it gets to about 80, my oncidiums seem to like it I have 3 blooming and 2 in spike and 1 phal with a tiny spike, so your temps should be fine