It is important to occasionally re-pot your bonsai tree in order to promote tree health, root growth, and ease of watering.Over time, the soil is drained and even with frequent fertilization looses valuable nutrients necessary to your bonsai. Timing is also important and tree’s should be re-potted in late fall or early spring when dormant. Young, small bonsai should be re-potted every year or every other year, and older more mature bonsai should be re-potted every 2-3 years.
Does My Tree Need Re-potting?If you do not know when your tree was last re-potted, or you think it might be time to re-pot, examine your tree. Is the soil hard? Does it absorb water poorly? Are there roots crowding the edge of your pot? If so, it is time to re-pot.
Removing From The Pot:
First, if you lightly water the tree, it softens the soil and makes the re-potting process easier. Second, it will probably be a good idea to either take your tree outside , or place plastic on your work area to prevent making a mess. Tilt bonsai pot on its side. Gently loosen around the edges with a butter knife or small gardening tool. Tap the pot with your hand to loosen soil and gently take your tree by the base and loosen. Do not pull on tree and be very careful to prevent damage. If it is difficult use the handle of your gardening tool and push up through the drainage holes to push the root ball out.
It is necessary to remove the dirt from the roots. Be very careful so as not to damage the roots. Gently shake out the roots and using a small thin implement such as a metal gardening hook, chopstick or anything similar, loosen the dirt from the roots. After removing at least 1/2 of the dirt, gently run your fingers through the roots and loosen more, it is best to keep doing this until at least 3/4’s of the old dirt has been removed. Either spray roots with water or wet them under a faucet to keep them from drying out.
Trimming The Roots:
As unpleasant and harmful a task as this may seem, it is very necessary, and if done right does not harm the tree at all. First, you will need a very sharp pair of cutters. Tree roots are tough so be prepared to sharpen and as always when working with cutting tools, be careful. You should start with trimming the thick brown roots that were growing near the edge of the pot. Remove between a third to half of these while being careful not to damage to many of the small feeder roots. Then, look at your pot, check the depth and then trim the small roots on the bottom of the tree till they will be half of an inch from the bottom of the pot. If you have damaged a great deal of the feeder roots, don’t worry to much. The tree will probably be fine, though you should trim the branches more heavily to prevent dying.
If you are using your old pot, clean thoroughly before proceeding. Place a wire mesh over the bottom of the pot thread a thin wire through the mesh and leave sticking out of the pot. Then create a thin layer of fine gravel over the mesh. Add a similar layer of soil and create a small mound where you would like your tree to be placed. Usually in the back and slightly to a corner. Next place your tree in the pot and spread roots evenly throughout the pot. Adjust tree until fully satisfied with height and position as it will be 1-3 years before it changes position.Twist wire around the root ball, make snug but not tight as this will damage the roots. This can be removed in a month or two when the tree is firmly in place. Next, add soil until it covers the base of the tree. Tap sides of the pot to settle the soil and add more until it is back to the required level. Thoroughly water the tree, add more soil as it settles so that your bonsai is buried up to the base of the trunk. Be sure that all roots are fully covered.
Final Step: Pruning
You will want to prune the branches of your tree so that the newly trimmed roots can support them. Do not remove a great deal of branches, and do not change the general shape of the tree unless desired. Remember not to fertilize for at least a month after re-potting, and remember to remove the wire from the roots after a few months. Finally, keep your bonsai out of extreme temperatures such as direct sunlight or drafts. Congratulations, you have re-potted your bonsai!