This is a birch that I recently got from a flat roof that was going to be renovated.
It was the beginning of June and the tree had much more foliage than it has now. The rootspread was incredible. It was well over 4 m2, under the insulation on that roof. The insulation was pushed up as good three inches, the thickness of the roots. Although it was high summer, I needed to have it and I needed to get into my car with as much roots as possible. I managed to get about 2 m2 of rootmass in the back of my car and drove home. I selected as much fibrous roots near the base and managed to bend more flexible roots so that the fibrous roots were near the base.
In order to make it survive a lot of foliage had to go.
Now, about 6 weeks later, its growing and I fertilized it with a low dose of chemical fertilizer.
It will be at least another full growing season in its container. After that I hope to be able to work the roots.
Obviously it's going to be a multitrunk bonsai. With 5 of 7 trunks. Should be possible in 4 to 5 years to get a basic structure.
Preserving the deadwood might be a problem. Anyone ideas about this?