20 yrs? Everything you mentioned is more than cold hardy to the UK, even up north, so I don't understand why you'd be protecting them anywhere (except possibly in a large pile of mulch)? And why treat deciduous like that ("dimly lit, frost protected")? Without leaves frost protection is rather pointless, but in any case it depends on the individual species of course.

Thanks for your comments. When I think back I've always put them away and out of the frost and coldest parts of our winter. Quite possibly because of advice I had received when first starting out and I have never questioned it. I was always told that the soil shouldn't remain frozen for too long(1 week maybe)before it is given a chance to thaw for fear of damaging the roots. It all sounded perfectly logical so I did it. I don't seem to have rendered any damage to them so all is well but, as you point out, maybe I never needed to bother so much !!!!! In the absence of joining a bonsai forum such as this I haven't availed myself to any specialist advice but will look forward to learning from you all. Thanks again Larke.

Look up www.bonsai4me.com for lots of basic advice.

I use to live in North America/Pennsylvania.
My trees were overwintered in a cold-house. It was part of a 'hoop house' like you see in many garden centers, the bows and bracing/end walls stayed up year round and it was also part of my display area. In the late fall the trees were placed in there (before covering because that made it easier to fill it) then the cover was put on and the ends sealed.
I used white opaque plastic, there was a small door for access. The structure was pretty air tight and held some moisture, it was also dead calm so even on very cold days you could work in there.

It solved the problems of the soil freezing and thawing also moisture dissication due to cold dry winter wind.

If I get a chance I'll post what pics I have of the set-up, it was simple and worked very well. The trick is to keep it sealed, if it dried out too much I'd just shovel some snow in.

Bob

Thanks Bob, it seems you employ a sort of 'half-way house' in comparison with my possible over protection. I would be interested to see any photos of your set-up as I may well rig something similar for the winter where I display my trees.

Happy new year too.

Dave

If your greenhouse is unheated why not just put everything in there. That would offer about the same protection that Bob is talking about. Everything you mention should be able to stand temps down to -5 C easily enough particularly if they are protected from the wind. Jack

The problem with the greenhouse is that, on sunny days during winter, the temps will rise sharply inside. This 'can' put the trees into a freeze-thaw cycle which is just what you are trying to avoid. A cold house should keep them frozen (once they are) and remain that way until it begins to warm up in the late winter/spring.

That's the reason for the opaque white plastic.

Mine kept them right around freezing (or a little below) with no wind to suck moisture away from evergreen foliage and the tender branches of trees like Japanese Maples.

Another thing, for an existing structure like that, would be shade cloth or an opaque cover for the winter.
I've been in Nha Trang for the New Years but starting home today, I'll dig up the pics and post them when I get home.

Bob

Stowboy...I can't post any pics here for some reason, why don't you send me an email tuyhoabob@tuffast.net and I'll send them as an attachment.

Bob