The idea is to water the tress, let them leak out any extra water thoroughly and then close them into transparent nylon bags to keep the humidity from escaping from the tree.
I did the same before I left for the trip to Thailand.
The first 2 photos are of Japanese maple which is not yet a bonsai tree. It is just a tree I keep outside in the front yard and perhaps sometimes later I will make it a bonsai. It was in the outside unheated storage with a thermometer and in a separate bigger pot filled with wrinkled paper sheets for insulation. This winter had several very very cold days (-27C) and when I panicked I took the tree in January inside directly into the same transparent bag as the other ones. It did wake up and started producing leaves so it did survive several days in about -15C which in my opinion is quite a feat for that specie 🙂 Later I will update on this tree, when it goes outside.
The rest of the trees are in separate nylon bags and on my sons working table near the window. February in Finland is not so sunny to be afraid of cooking the trees (actually there was no sun all 2 weeks) so they can all remain where they are for the trip length.
When I closed the tree inside the bag I also wrapped a thread around the bag right above the pot upper edge. The idea was that when the water condenses on the bags walls they would leak down and I wanted them to end inside the pot, not gathered in the bottom of the bag where the tree will not be able to take it from.
After the trip I checked the trees. Several notices:
- All trees survived, at least none of them yet died and definitely not due to the bag treatment.
- Every dead leaf in the pot or hanging on the branch got fungus. This needs to be remembered next time when I close them, first cleaning!
- Though the trees look quite “wet” the pots are actually quite dry (as noticed on the janinbonsait page linked above). The tree sucks the water from the pot and evaporates it into the nylon bag. All is fine as long as the bag is still closed. I had to water a day or 2 after I opened them, they all got completely dry.
- Some of the leaves (ficus for an example) fell of the tree, I assume due to dryness in the pot or perhaps just because of non-standard growing conditions. Though the trees were near the window the light is insufficient for any tree to grow… survive maybe.