Since you have standing water at the bottom, you could get a glass aquarium heater to warm the water to 80 degrees. You would be warming the air through radiant heat from the water. You will have a problem if the water level drops and the heater is exposed to air.

Since glass is a poor insulator, you could wrap your terrarium in bubblewrap or some other material to prevent the heat from escaping so fast.

Hey Dave,

Thanks for the advice. I think I'll try something like that. The standing water is rather shallow, maybe 1-2". But I've read that I could put a big glass of water in the tank and put an aquarium heater in that? Same principle, different application. Or, I've read about a heating cable but I don't know if there is such a thing that can be fully submersed in water.

Thanks again for your input.

Jim

Jim
They make cables specificly for heating shallow water or wet soil. You will find them in Hydroponics stores. You can also get heaters built into pumps.
The problem with the aquarium heater is that you will have a warm glass of water as the heater will shutoff lol
Could you make the water deeper?? With a small air bubbler you could get the water to mix and distribute the heat. Make sure an aquarium heater stays underwater they will shatter if exposed to air.
gary

If you could make the water deeper (3"-4"), you could use a heater that is totally submersible. You would just need to figure out approximately how many gallons of water you need to heat and get a heater that is 3-5 watts per gallon (10 gallons of water would take a 25-50 watt heater). The main thing is the water level cannot be allowed to fall below the level of the heater or the heater will overheat and become damaged. They also have small heaters for fish bowls and such that will raise the temp of the water as much as 5 degrees above room temperature. You may be able to use 2-3 of them to help get the water warm enough. Again the water level would have to be deep enough to cover them completely but they do not appear to be as thick as the normal submersible heaters so 2" of water might be enough for them.

Here are links to both of the types of heaters I'm talking about. I use the first type of heater in all my fish tanks and they work great.

http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=12060&N=2004+113767

http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=12087&N=2004+113767

You could always used a fan to do this, I first used a rather large fan to draw the heat from the canopy to the inside of the set up, then kept a close eye on humidity and temp for a while, when I noticed a fast drop in humidity and a fast rise in temp I switched the fan out for a smaller one, I did this three times before I got the right sized (very small PC fan) for the job, now the humidity is perfect and so is the temp, please understand when Im saying what Im about to say that I am in no way trying to knock anyone elses suggestions! =) the heated water is not so good an idea, frogs and other critters like to cool down, some cool spots in you set up are important, and the most important cool down spot for frogs is....the water feature in your set up, and the possibility of your not being around one day that the water runs dry is not impossible, and lets not forget the very real fire hazard! My tank has natually cool spots, shaded areas of the tank, heavily planted areas, and Im sure yours does to, but it seems to me when a frog feels hot, uncomfortable, or just spooked, where do they jump? right into the water! Good luck with your problem. =)

Yeah, Im an idiot! LOL! Just got the title,"Heating a PLANT terrarium" DUH, stupid me! LOL! (but the fire hazard is still VERY real!)

Thank you to everyone for your suggestions. Let's see, 8mos have passed since I origninally posted this question. I made it through the winter/spring with no problem. Once the outside temps rose to the 70's, the tank got well into the 70's to near 80. BAM!!!!! Stuff started happening. My Masdevallia bloomed two or three times since then, a gorgeous dendrobium atroviolaceum bloomed for a couple months, my sophronitella violacea bloomed continually for over a month, haraella odorata bloomed twice. Now that things are cooling down, a Odontocidum Elke Stolz is spiking. So, clearly temperature was the deciding factor for blooming success. Now that the cold is quickly decending upon New England, I'm going to take these suggestions and put them into action. At least the warmer growing orchids will enjoy the warmer daytime temps. I think the other smaller orchids that haven't bloomed are cooler growers and I can't get the temp down into the 50's at night for them to thrive. But that's a question for another posting!!! Thanks again.

Jim

Could you post your plant list? I'm getting ready to start an orchid terrarium, and I'm looking for ideas for varieties.

I'm gonna try to stick to warm/intermediate growers so that I only have to worry about warming the tank, and not cooling as well. What did you end up doing to control the temp? Or was it solely the free heat from the summer months that did it for you?

aes123,

I have different orchids that I tend to put in an take out of the terrarium, depending on how they like or dislike the conditions. But, to answer your question, right now I have Trisetella didyma (bloomed and is spiking now), Haraella odorata (bloomed multiple times), Gastrochilus japonica (blooming now), Den atroviolaceum (in bloom now and has bloomed many times before), Masd 'Ruby Slippers' (multiple blooms), Sophronitella violacea (bloomed and will spike soon), Trichoglottis triflora (just ending blooming like crazy), Meircyllium trinasutum, Cochleanthes discolor, among others. My problem is that I impulse buy on what looks good without really thinking a whole lot about culture. Most of them though are intermediate/warm and humidity lovers that like medium light.

I hope that answers your question......albeit a few months late.

-Jim