Now is a good time to repot. However, it would be best to do what we call HBR (Half Bare Root). P. parviflora is most commonly grafted onto p. thunbergii roots, but p. sylvestris is becoming more common, especially with growers in Washington and Oregon. Sylvestris roots grow so strongly that a full bare root can be done. If you are certain the root stock is sylvestris, go ahead, but otherwise do an HBR. First, you can cut off the bottom third to half of the root 'ball' after you've knocked off the plastic pot. Then you will use your trusty root hook and maybe a little bit of water jetting with a garden hose to remove the nursery soil from the roots on only one side of the trunk. Then you will prune the roots and pot the tree in substrate and next year finish the process bare rooting the other half of the roots.
Frequently I invert the destination pot and use the base (now top) as a template for trimming the roots.
Life will be easiest if you repot into a pond basket or colander. The big box stores usually have ones that are 8x8 that will last many years. Roots will get air pruned in these containers, developing the root pad needed for a bonsai pot, in situ. Otherwise, repotting every year or two years is necessary to affect the root pruning that is required. If you are taking this latter route, be sure to do all
styling work before repotting.
Generally, you will want no more than two branches at a node/whorl. You want the lowest branch to be the heaviest an to be on the right or left side of your chosen front. Then you want a branch on the opposite side that isn't quite as heavy and you need a branch behind that will give your design depth (otherwise your tree will look 2D just like a pic in real life, which is actually very 'boring'). Then you need something for an apex. This is all that is necessary for a bonsai. You may want more (and some designs will need more) and/or you may not be able to decide which to remove right away. That is okay. I must confess that I am very reluctant to cut branches and must keep reminding myself that these 4 structural elements are all that are necessary. If you already have wire on hand, you may want to do an initial styling, selecting branches and wiring them to positions that assure sunlight gets to all the foliage and into the interior, near the trunk. On the other hand, late next winter or early spring, is a much better time for wiring. Right now, the bark is easily torn off the stems.
Branches can be removed anytime you want. Now until late fall may produce an amount of resin bleed that you find undesirable/disturbing. By the time leaves are falling off the deciduous trees, this won't happen.
Okay! Now we're having fun, right?
