Keeping Bonsai frost free over winter.

[Mitty]

I have about 100 Shohin Bonsai trees. In the Midlands in England , we can get some frosts , serious enough to damage or even kill My Bonsai Trees. I lost 2 last year. As I purchased a few decent trees from Germany recently : Hornbeams , Korean Hornbeams and Quince trees. I came up with the idea of buy heating wires , but rather than using them underground , using them in the open winding them around my bonsai pots. I went ahead and after about £100 , I had 4 reels in soft orange wire. I used them as I said winding each pot once around and then on to the next pot. I had to buy a good extension wire and a 4 way adapter covered by a large Tupperware box. Well it worked , in fact it was a success and it just stopped any frost laying around each Bonsai pot. It works very well for me. I did find that the orange wire was superior to the narrower green type. All available on ebay . Maybe you have heard this idea before. But for ease of use and to allow rain to reach your trees , might appeal to others. Anybody else tried this...……..maybe mad but you can leave the trees where they are and don't have to cover them , except during seriously cold weather. There is not enough heat to start the bonsai trees budding.

 

[Tieball]

Never tried that...the heat wire. Frost is a problem for me only in late spring. My winter is a blanket of snow and there are no leaves or buds to damage. Frost in my winter during dormancy is not a problem situation...business as usual. In the late spring, we can get frosts up to the end of May, when buds are open or leaves have formed, when I hear of a frost warning I go out and mist the trees and that mist freezes as a protection layer. Fruit growers use a similar technique.

I have missed frost warnings though. At a time when buds were breaking and some leaves firmed. A couple years ago a late May frost killed off all the leaves on several trees ground growing. Nature came through and just sent out new buds and leaves a couple weeks later. The trees, Celtis Sinensis, came back healthy. American Elms I have just ignored the frost and continued unhindered growth.

I have heard of a frost-cover cloth that can be used but have not used it and am not familiar with it. It sounded reasonable....but I was just guessing about it working.

If there are no open buds or leaves forming I don’t worry about frost.

 

[JudyB]

I use heat mats, they do the same thing but with a lot less trouble. They are called Propogation heat mats, they are run by thermostatic control so you can determine when you want them to come on and go off. They keep my roots/pots from freezing all winter, I keep them at about 34 F. If you want a link I have one I can throw you.

 

[K_10_G]

Ryan spoke about this on Mirai’s Winter Care BSOP stream

Around the 36 min mark. Not something I’ve done yet but an interesting technique with the pumice.

I have two small heating horticultural heating pads. Like these ones

https://www.amazon.com/Seedling-Hyd...ocphy=9003938&hvtargid=pla-350506522936&psc=1

 

[rockm]

I have about 100 Shohin Bonsai trees. In the Midlands in England , we can get some frosts , serious enough to damage or even kill My Bonsai Trees. I lost 2 last year. As I purchased a few decent trees from Germany recently : Hornbeams , Korean Hornbeams and Quince trees. I came up with the idea of buy heating wires , but rather than using them underground , using them in the open winding them around my bonsai pots. I went ahead and after about £100 , I had 4 reels in soft orange wire. I used them as I said winding each pot once around and then on to the next pot. I had to buy a good extension wire and a 4 way adapter covered by a large Tupperware box. Well it worked , in fact it was a success and it just stopped any frost laying around each Bonsai pot. It works very well for me. I did find that the orange wire was superior to the narrower green type. All available on ebay . Maybe you have heard this idea before. But for ease of use and to allow rain to reach your trees , might appeal to others. Anybody else tried this...……..maybe mad but you can leave the trees where they are and don't have to cover them , except during seriously cold weather. There is not enough heat to start the bonsai trees budding.

You are making the mistake of assuming that trees need to remain "warm" in the winter. In doing so, you're setting yourself up for some dead trees.

From what I can make out, the average winter in the midlands is not all that cold, with not much hard winter weather. The species you've listed are pretty cold hardy. I've overwintered Korean and North American native hornbeam in my backyard under mulch for decades with no supplemental heating. I think you can probably do the same. I get hard freezes and sometimes deep cold (as in the 3F temp last week during the polar vortex). I keep collected trees native to Texas and La., as well as a couple of species of hornbeam, outside under deep mulch piles with no worries. I've done it this way for over 20 years.

You have probably lost trees not to frost, but to improper preparations and storage. I'd also guess 'overcare' also had a role. A lot of newcomers tend to coddle their trees, avoiding frost and freezes in the fall and through the winter. That's a mistake. Both frost and even freezing play a dynamic active role in preparing trees for winter. Wrapping them with heating elements is not a great solution. Understanding the process trees go through to survive winter and adapting your care and storage to those processes is a better way forward.

For starters, read these:
https://www.evergreengardenworks.com/dormancy.htm
https://www.evergreengardenworks.com/frzekill.htm
https://www.evergreengardenworks.com/overwint.htm

Bald Cypress, elm, hornbeam, azalea all under this no supplemental heat. Under the snow, the pots are covered by eight to ten inches of hardwood mulch