Posts tagged “Rhododentron

Repotting a Very Rootbound Satsuki Azalea ‘Kaho’

Repotting mature trees is different than repotting trees in development. Mature trees are usually repotted for maintenance purposes, so the root work is less dramatic and much less technical than the sort of work used for trees in development. At a recent workshop, I observed the repotting of an extremely root bound imported Rhododendrum indicum ‘Kaho’. This is a species that I have never worked with since I sadly don’t have the proper overwintering environment for azaleas. Still, its fun to watch and learn đŸ™‚

The bonsai in question. The owner has had this tree for 3 years. He believes that it has not been repotted for 8 years, and had reached the point that water could no longer penetrate the root ball. As a result, the tree is weak.

The kanuma soil has almost completely broken down, and the pot was absolutely crammed with the fluffy roots that are characteristic of azaleas. The first step after removing the tree from the pot was to clean away the surface soil.

One of the most important tasks in the repotting was cleaning out the bottom of the rootball, all the way up to the base of the trunk. This area is most prone to rot, so cleaning it out well allows it to be inspected and refilled with fresh coarse grade kanuma. About half of the excavation is complete here.

A saw was used to trim only about 1.5cm of roots all around the perimeter. Since the tree is weak, a more aggressive root reduction may have been detrimental to the health of the tree.

All hanging superfluous roots were carefully trimmed back so that they were flush with the rootball. This picture shows the extent to which the bottom of the rootball was excavated.

The tree is going back to the same pot. There was a unanimous agreement that this pot is unsuitable for the tree, although the owner will be repotting the tree again next year once it regains strength. Hopefully he has found the right pot by then :)

With such a deep "pit" in the bottom of the rootball, simply making a mound of soil in the bottom of the pot is not good enough. Thee tree was held upside down and coarse soil was filled into the cavity. A chopstick was used to fill all of the voids. This is a step that is unique to trees with mature root systems - particularly azaleas.

To prevent losing the soil, the pot was also put on upside down. Getting the tree at the correct height in the pot can be tricky when this method is used, but this time it worked just fine the first try. Someone commented that this must be how they repot bonsai in Australia :)

The tree was securely tied into the pot, and the pot was submerged in water for several minutes, thus completing the repotting.