I believe this to be the most important technique. Pruning the roots properly ensures that Bonsai stay small and grow
vigorously.This is always done in the early spring before any buds open and preferably after the danger of severe frost has
passed. Newly pruned roots do not stand being frozen on even the most hardy tree!
First remove your Bonsai from its pot. I cut any retaining wires from the base of the pot first and slide a blunt knife
around the inside edge of the pot. Hold the tree by the base of the trunk and carefully lift it out of the pot. The roots
should be tightly packed, this means the tree has grown well last year.
Gently comb out the roots using a root hook. Work from the centre outwards.
Be bold! Cut at least half of the roots off from the outside. Cut any thick roots back and use a wound sealant if necessary.(Birch
bleed a lot so this is necessary for this species) You should ensure the base of the roots are flat so the Bonsai sits well
in the pot.
Spread a layer of compost at least 2.5cm deep in the base of the pot and settle the tree onto it. Thread a length of
wire through the roots and out of the pot through the drainage holes and pull down and twist together under the pot. This
will hold the tree in place until the new roots grow.
Now fill the pot with compost, ensure there are no air pockets by prodding the soil into place with something like a
spoon handle or lolipop stick. Smooth the soil surface, add some moss if you like and the job is done.
Water well and keep the Bonsai in a sheltered, frost free place for at least two weeks. I find I need to do this every
spring, the only exceptions are my older trees which I now do every other year.