Hello! I have a Chinese Elm, a Green Mound Juniper, and a Flowering Satsuki Azalea. I have had the Elm for a couple of years now and have kept it inside so far. I recently purchased the Juniper and Azalea, and they are outside. I'm preparing for winter and wanted to see what your thoughts are about my possible set up.

I have a plexiglass greenhouse that I plan to use to keep the bonsai in during the winter months. I live in Iowa which is zone 5a (-20 to -15 F or -28.9 to -26.1 C). Do you think I should put a warming mat under the pots to help keep the roots warm enough?

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Would it be preferable if I kept the Chinese Elm in the greenhouse instead of the house during the winter months?

Thanks for your help!

Congrats on keeping the elm alive indoors for a coupple of years. That is really impressive, I have not seen anyone done this before. Please share a photo and describe your care.

The juniper will proboably be fine without greenhouse or heating. It is fully hardy to zone 3, planted in pot to zone 4. The Azalea will be more of a challenge. In ground hardiness 7 to 9, but in pot a lot more fuzzy. Here in sweden people keep them frost free during winter. I keep mine in unheated greenhouse (zone 7), but I must confess I am not totally happy with health and development.

Here are the three bonsai. I've kept the elm in a sunroom that stays a little cooler than the house. It went dormant during the winter months and then started growing again this last spring.

Do I need to be worried about the roots freezing on any of these plants? Part of me thinks no, but I want to make sure before I let the trees stay in freezing temperatures all winter long.

Thanks for the response!

All of them can take freezing temperatures. But it is important to understand that wile the roots is solid frozen the tree cannot drink. The demand for water is very low in winter, but frozen for a long time can still mean that it dries out. Especially if they are exposed to dry cold wind.

How cold is cold is your sunroom? Is it possible to keep it at 5c all through the winter? That would be good for the elm and azalea. The juniper should be outdoors all winter. Preferably burried in snow.

It's not possible to keep the sunroom that cold. However, I do have a small greenhouse that I can keep the elm and azaela in to protect from wind. How should I keep it warm in there? A heating pad?

Should I leave the Juniper in its pot while I leave it outside or should I transfer it to a different pot? I'm curious if I should be concerned about the pot breaking.

I would leave the juniper in the pot. If it is a quality pot ment for junipers it will make it. If not it will break and you get a chanse to get a quality pot for it in spring.

Why cant you lower temperature in the sunroom to 5c? Lower temperature in the sunroom will be a lot better than starting to heat one more area.

Makes sense about the pot - good excuse to get a quality pot of the current one breaks!

I can't lower the temperature to 5c because I live in the US and can only lower it to something in Fahrenheit. Ha, just kidding, a little non-metric humor for you. I can't lower it because it's connected to the house and not totally separate - it'll be a little cooler but not by more than a couple of degrees from the rest of the house. How about keeping it in the garage? Does it need light even though it's gone dormant?

Haha! Did you know that Fahrenheit is a blast from the past? Nowadays only used in the Bahamas, the Cayman Islands, Liberia, Palau, the Federated States of Micronesia, the Marshall Islands and one more insignificant country.

Bad jokes to the side.....

The trees do not need much light when dormant. What is the temperature in your garage in winter?

I did not know that there are a few places that still use Fahrenheit, other than the US of course!

I have a heater in my garage that keeps the garage at around 5c. There are some windows as well, so it's not totally void of sunlight.

Do you think the azaela and elm will do best in that environment?

I would put all three trees in the window in the garage.