The weather patterns have been way too odd the last several years. I watch my trees and the weather channels. We have had early 25F December weeks and THEN 50F weeks.
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MOST ( if not all) of my trees will take overnight 30F. Ok. Snow is fine…nock the snow off slender trees.The tropicals go in at overnight +45.
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I DO NOT get worried untill the first HARD FREEZE. Well after leaf fall. (The only trees I have lost to obvious winter kill were a black pine and horse chestnut I took into a garage…)
I start preparing winter storage and slowly move the herd that direction. Decideous first. Pines last. Some stay out untill 20F days. I hate to do it ALL in one cold day…
Oh ya… do not forget the mice poison in covered cups with small holes…
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Read: Winter Care below 20deg F
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And: Winter Storage Concerns
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Hope this helps. I wish I had Mirai 40 years ago! All I had was the 1960’s Sunset Magazine book.
Enjoy… Bonsai on! (Haute Bonsai!)