Time for Repotting

Springtime is an important time with bonsai, the primary activity being repotting. How do you decide when is the right time to repot a tree? There is no point trying to pre-plan repotting on a particular day; the tree dictates the right time. I started repotting in February hardly what we would classify as spring, and the first tree I repotted was a Lilac.

With most deciduous and conifer trees repotting should be done when the tree emerges from dormancy. So how do we recognise this? The tree shows us, as buds swell and burst into life that’s the right time.

On this quite young Larix (Larch) look closely and you can see that this years buds are opening to reveal a vibrant green shoot.

Hence time to check whether it requires repotting. Young trees normally require more frequent repotting than mature ones.

Before starting repotting best make sure that you have everything required.

Tools include a root hook or root rake, a chopstick or something similar, wire and wire cutters, mesh and the appropriate soil.

(I don’t intend to discuss soils as that tends to be a personal choice, if in doubt ask a local club member)

The soil in the image above is a mix 60% Akadama and 40% Pumice but I frequently add a bit of sphagnum moss.

If you are using a different pot to that which the tree is currently in prepare it now to reduce the time that the tree root is bare. If using the same pot this will need to be done later.

First make sure the pot is clean and then fit mesh over the drainage holes using figure eight clips made from wire.

Then attach the tree securing wires either via holes provided or by threading through the drainage hole and over a bar on the underside of the pot.

Okay, so now you are about ready to repot the tree. The first task is to remove it from the pot. Start by cutting the securing wires on the underside of the pot.

You may need to free the roots from the inside edges of the pot. You can do this easily with a knife or root hook by carefully sliding around the edge of the pot, as shown opposite with this Larix group.

Next lift the tree from its pot and examine the roots.

The image below is of the roots of the young larch pictured above in the first photograph.

For bonsai the ideal root system is one of fine fibrous roots, rather than the longer coarse roots on this tree.

More important is the condition of the roots, so you need to check for smelly roots that are soft and rotting. Hopefully you will see roots with a lot of fine root hairs. These are the import part of the root system.

Roots which are thick, long, and wrapping around the pot, such as those in the image opposite are undesirable and need to be dealt with to promote the fibrous root system that bonsai thrive on. This is one of the tasks I personally found a bit worrying. Long roots need to be trimmed back to strong growth with fine root hairs.

How much root can you safely remove? This depends on the overall health of the tree and the condition and the spread of the roots. Sometimes roots are not of equal strength around all of the root system, so you may need to remove more in some areas and less in others.

The image on the left shows the root ball after removal of the long unwanted growth. The roots now should be teased out around the perimeter with a chopstick or similar tool to create a radial growth pattern as far as possible.

About one third of the root has been removed which created enough space to allow new root growth to develop. I keep a pair of scissors only for use on roots, and importantly clean them between use.

Right, almost ready to put the tree into the pre-prepared pot. Before doing so place some soil in the pot, the usual method involves creating a mound in the pot below where the trunk will be positioned, this can be either centrally or offset.

Next position the tree, with the nebari (visible root spread) shown to best effect and the front correctly positioned.

Now gently twist the tree and roots in a circular motion to ‘bed’ the tree into the soil. Position the securing wires avoiding cutting into roots, (If necessary use plastic tube over the wire where this crosses roots if this cannot be avoided).

Using a scoop or something similar fill the pot with soil and gently work this into the root ball using your favourite chopstick, or as in this case a piece of garden cane. Now it is time to secure the tree with the securing wires by carefully pulling the wire with pliers twisting as you pull.

Lastly water thoroughly. But remember not to feed the tree for approximately six weeks to allow new root tips to develop as fertilizer will be detrimental to their growth!