We repot our bonsai every year, unless we know they have plenty of room to grow in the pot. You can check this by removing from the pot to check for root bound or if there is enough room for the bonsai to grow for the year. Most Young tropicals, or those in small pots will need repotting every year, we are strong believers in repotting every year. This will help the bonsai get the nutrients from fresh soil, plus give the bonsai room to grow in the pot, keeping it healthy. The best time to repot tropicals is when they are strong and vigorous, in late spring through early summer is best. For non tropicals, deciduous and evergreens repotting for us, is done when the tree is dormant and the buds are just starting to swell for spring. The exact time depends on your area, and also the climate for the year. If you live in the NW as we do the repotting comes earlier than say if you live in the north central area of the US. Usually all the repotting is complete by the middle of March in our area. Repotting is an important part of keeping your bonsai healthy and growing and usually involves root pruning. The bonsai needs room to grow new roots so when repotting some of the roots usually have to come off to make room. We usually take about a third of the root mass off, all around and on the bottom of the bonsai. All when straighten and shaping the root ball. You can get more info on repotting from reliable book, bonsai hobbyist, or local bonsai club.
Basicaly, heres the jest.
Take the bonsai out of the pot, check the roots and soil to determine if repotting is necessary. (most of the time yes, it is.) Place it (the tree) on the table, comb out most of the root ball using a root pick or other tool. Cut off about a third of the roots all the way around, and on the bottom of the bonsai. Prepare the pot, (drain screen, wire, soil in the bottom etc.,) you can use the same pot if you want. Place the bonsai in the pot, place “bonsai soil” on top and work it in using chop stick or something similar. Place small pebbles on top of the soil if you so desire. Water well, until it is running out the bottom, and then do it again. Im sure I will get a lot of comments on this article but, That’s it in a nut shell… But please read on.
This is what we practice this topic is widely argued, there are a lot of different ideas, our best recommendation is to try several techniques and see which one works for you. Plus as you learn you are gaining the experience as every master bonsai artist has had to do.
One of the bonsai artists at EBG Group
Working on bonsai for over 30 years.