I find it interesting when people ask, “What do you do with your trees during the winter? Do you take them inside? Won’t they freeze? It gets so cold outside!” I then ask them, “Do you take your outdoor trees inside? What about your live fences? Have you ever seen a maple growing in the tropics?” Of course not. I don’t give them a hard time though because this question isn’t that outrageous but something that needs to be clarified for people interested in or beginning to grow trees.
All trees, shrubs, grasses, mosses, flowers and all other plants have grown and genetically adapted over thousands of years to particular parts of the world. In bonsai the only thing that changes is the natural size of those plants, the rest genetically, needs to follow the natural environment that those plants have adapted to. Plants that grow in temperate zones must have winter dormancy to re-charge for the next growing cycle. It is just the way that they have adapted. To bring a deciduous or conifer inside towards the end of summer would result in the continual growth of that plant. The poor thing would think that it’s spring or summer all the time and eventually it would die of exhaustion. But, because Bonsai are grown in shallow containers we must protect their roots. In their natural environment, the roots are hidden many meters underground where frosts will never penetrate and the top parts of most temperate trees are much more hardy then their roots. This is also due to the fact that the plants’ energy has moved in the root system. Also, most conifers are much more hardy in general regarding frosts and what temperatures they can handle in comparison to deciduous trees and plants.
About three weeks ago, I decided to put all the trees into their slumber area. Since then, we have had a really warm December and I am jealous of all the snow that the Pacific Northwest is getting now whereas the Alps and central Europe have… nothing.
Anyway, the day after I put my trees into their winter storage, we had the first real frost and sub zero temperatures that night as well as some snowfall that Monday, yes snowfall! Then.. it was gone and the following week temperatures went back up into 5-10 degree Celsius (41-50F) so go figure.
I don’t have much options on a balcony so my method looks like this. I place the former bonsai ‘bench’, which is nothing more than the top of a former table, on the balcony floor at an incline so that any water can find its way out if it builds up in the future. Then I cover the board with 3 layers of carpet which are then covered with some industrial plastic to make sure that they don’t get soaked. Next, I surround the board with 3 other boards to create a sort of tub if you will. Also new this year, I place this tub on the right side of the balcony to keep the trees from receiving sun during possible warmer days in March so that they don’t come out of hibernation too early. When trees begin to grow early in March or even early February because of a warm stretch, they face the possibility of freezing again when the temperatures plunge randomly, which they do during late winter and early spring.
Next I place the trees together so that they all nicely fit. Here you can see the plastic over the layers of carpet that insulate the trees from frost and wind.
Finally I like to use Sawdust or leaves to cover the trees to further insulate them from the frosts and wind that our central European climate USUALLY has.
This is a few minutes after the morning sun landed on this glass but you get the idea. The first true sub zero night happened right after I put my trees into winter mode. Five days later the temperatures went back up and I still have yet to see some real winter conditions here since about 4 years ago when we had a stretch of -15C for two weeks in February. Hasn’t happened again since I’ve been here.