For our February 2007 meeting the club came together for a night of repotting and root work. Special thanks to John Edwards for taking charge of our newer members. Repotting can be a mystifying process for people who have no knowledge of the proper way to do it. John provided help and instruction to more than a half dozen people, all of whom I’m sure were very grateful.

As I mentioned in the article about this program, repotting is a fine art in many ways. You should aim to refine the surface roots of your tree with every repotting. For example, on a healthy growing maple, cut off downward growing roots so that new finer roots sprout from the surface roots. Planting trees in wider, shallower trays will encourage the surface roots to run and fatten up. Consider also that trees sometimes look better with more or less root showing than has been the case before repotting. For pines and some other conifers, a twisting mass of roots spreading in every direction helps to complete the look of a tree. Avoid at all costs burying all the roots which will make your trees look like a stick in the mud.

Soil is a vital component in maintaining a tree in top health. Mix your bonsai soil while all components are bone dry and sift to remove fine particles. If the soil is too wet to dry out practically, sift the components underwater to remove the dust particles. If you neglect to sift out the fine particles the bottom of your pot will become clogged and the roots will sit in a swamp all year long, causing diseases and poor general health. There are as many formulas for soil as there are bonsai enthusiasts. Some include only a few components and some include a lot. The most important thing to remember is this: roots need air as much as they need water. When you pull a tree planted in heavy soil out of a pot all the roots are circling at the bottom and along the sides. If you have good airation in your soil you will find a network of fine roots in the middle of the pot as well. This network is the key to a tree in good health, and to the tree maintaining vigor after repotting.

Akadama is the most commonly talked about soil component in bonsai. It is expensive and it is Japanese…is it worth the money? That question is one that you will have to decide for yourself; some people use pure akadama for their trees while others balk at the expense. Akadama is a baked clay which, although inorganic, acts like organic material in the soil by retaining fertilizer and micronutrients for the tree to absorb between waterings. The cheaper alternatives to akadama are fir bark or other small barks or any of a number of fired clay products. Oil-dry is widely talked about on internet chat rooms as a cheap and effective alternative to akadama. It is a fired clay and is designed to absorb oil spills. It is far less expensive, but so far I have not seen or heard any evidence (based on head to head comparison) that says it does the job equally as well as Akadama or fir bark.

Pumice, either imported from Japan or quarried locally is another common soil ingredient. Pumice is lightweight and does not decompose in a pot. It will maintain the matrix of small pockets in the soil even once other components start to decompose. Pumice is frequently used as the “drainage layer”, the layer of soil just covering the bottom of the pot which helps to maintain free flow of water throughout. Lava rock is much the same as pumice, and is also available locally, it is slightly heavier. Decomposed granite is much much heavier than the other soil ingredients but using a small amount in the soil will provide the potential benefits without making pots terribly heavy. Horticultural charcoal is another ingredient which, when used in small amounts, can provide an extra bit of insurance.

There are a number of steps in the repotting process which should be followed as closely as possible. Repotting of a newly collected or young tree can differ substantially from repotting of an older established bonsai.

1. If you are using a different pot than what the tree is already planted in prepare the pot before beginning. Cover drain holes with screen and add tie wires. Then, start by cutting the old tie wires and bending the stubs and the wires holding screening over so that they are not touching the pot and can move freely through the holes when you pull on the tree and rootball.

2. Using a root sickle, cut along three sides of the pot, removing some soil and the mat of roots that grows against the side of the pot. Angle the sickle so that the rootball is smaller than the inner rim of the pot if the pot rim hangs inward. Cut one long side and the two short sides on a rectangular pot, or two-thids of the way around a round pot.

3. Tip the tree out of the pot. If you are transplanting into the same pot take this time to set the tree aside and wash and re-wire the pot. Do not scrub pots with wire brushes or other harsh cleaners. Pots will gain patina over time, so wash only natural bristle brushes, do not use petroleum products to clean. If there are calcium deposits on the pot then can be covered by an application of walnut oil, which will make the pot look clean.
4.Lay the rootball on the side that has not been cut, with the tree hanging off the side of the table. Using a three-prongred rake or bent tweezers, rake the bottom of the rootball and then cut it flat with root scissors. If there is not a cohesive rootball simply trim the roots even and flat. You can make the bottom of the rootball concave by trimming more in the middle than on the edges, but do not make it convex because that will make it harder to tie the tree into the new pot properly.

5. Clean off your table and set the tree on it. Start working around the edges of the rootball using a root hook or tweezers or chopsticks. Comb the roots outward removing old soil. Once a tree is in good soil it is not neccesary to bare-root it every time it is repotted. If the tree is in old soil you can bare root only half of the tree if you are concerned about the tree’s health, leaving the other half for the next repotting.

6. Once you have finished cleaning out soil cut the roots around the rootball, leaving the roots slightly longer than the soil that remains, but smaller than the size of the pot. Do not curl roots into the pot except in extreme cases.

7. Place a drainage layer in the pot, and add a small mound of soil over it. Make sure all the tie wires are headed out of the pot and will be accesible.

8. Place the tree over the mound of soil and gently but firmly twist and press down slightly to firm the tree over the new soil.

9. Add a small amount of soil around the tree and chop it in gently
10. Tie the tree in; there are a thousand different ways depending on size, placement and number of holes and other factors. Some practice will teach you the best method.

11. Add more soil, chopping in gently to fill pockets. Try not to chop so vigorously that you penetrate the drainage layer or that you damage the roots excessively. Generally, use a smaller size soil on the top than on the bottom of the pot, it will retain moisture closer to the surface of the pot.

12. Brush and pat the surface of the soil flat and give the pot a tap or two to further settle the soil. The soil should not be mounded, and should ideally be slightly below the lip of the pot so that it doesn’t run off when you water. Mounded soil causes uneven dustribution of water when you are watering.

13. Water the pot until the draining water runs clear.

14. Do not fertilize newly repotted trees for 4-6 weeks with organic fertilizer, 6-8 weeks with chemical fertilizer.

Tags: Beginner, Repotting, soil