For future reference, here's my step-by-step guide to how to repot a tree:

The tree in question is a larch, collected from a friend's plantation about 18 months ago, which has been growing a pot in the stoney clay soil of the site since then, hence the early repot this year into more suitable soil. The basic sequence would apply in exactly the same way to any other tree (eg. nursery stock or an established bonsai, except in the latter case you may well be re-using the same pot).


Step 1: Choose a working space, collect together tree/s to be repotted and new pot/s:




Step 2: Prepare pot by making "butterfly" of stiff wire, attaching thinner wires to this and feeding them up through the hole in the base of the pot, leaving the "butterfly" on the underside:




Step 3:
Spread out thin wires and use sphagnum moss or gauze to cover hole to prevent soil mix falling through:




Step 4:
Prepare the soil ingredients. First, seive each ingredient with a fine seive to remove dust and fine particles:



After:


Step 5:
Measure out the ingredients (after sifting) as appropriate for you own mix. I'm using equal parts organic matter, horticultural grit and cat litter. The organic matter is 50% pine bark, 50% leafmould:




Step 6:
Mix the soil ingredients together, note how coarse and separate the particles of my mix are; you shouldn't be able to mould your mix into balls when wet. If you can, you didn't sieve it well enough - do it again.




Step 7:
Remove the tree from its pot and shake or (my preferred method) wash the old soil from the roots:




Step 8:
Trim overlong or overthick roots, but ensure you leave enough fine "feeder" roots to support the topgrowth of the tree (compare this image to the last to see how much I've taken off):




Step 9:
Place a thin layer of soil mix in the base of the new pot and arrange the tree. Use the wires to secure the tree in place so it can't move about:




Step 10:
Finally, fill the pot with the rest of the soil mix, making sure the space underneath the tree's roots is not empty, then water in well and add moss if you like. TA DA!




Kath
UK - Zone 8

"People will forget what you said,
 People will forget what you did,
 But people will never forget
 How you made them feel."