Sunday, 19 January 2014

Japanese maple repotting


It's been a winter with mild temperatures and a lot of rain in southern England. Some of my maples have already started budding so I began to do their repotting sooner than I had planned. These maples seem to begin their summer growing based purely on average temperature.

The inspection of the roots is important. Soils and growing conditions are of great interest to bonsai growers - as you can tell by the number of opinions on soil mixes out there. It is also an opportunity to get hands on and fiddle as opposed to sitting back and watching them grow ever so slowly.

My maples are grown in the classical Japanese method of graded layers of Akadama. A coarse drainage layer topped with finer particles for the roots. This is the technique I have seen in many of the old Bonsai Today magazines which had translated articles from old Japanese nurseries. I am deviating now by using a drainage layer that doesn't degrade and introducing more ingredients into the main body of soil that won't degrade.

I suppose a few hundred years had taught them how to grow maples in an optimum fashion with Akadama. They do write a great deal about how the roots effect the branches of the plant above - so I'm hoping that my root ball full of lovely fine evenly radiating roots is going to give brilliant foliage this year.

Overly strong big thick roots can result in some parts of the foliage getting too vigorous and giving excessive inter-node length.

It seems to me that as the number of buds was increasing that the inter-node length was getting shorter.

They advise adjusting the drainage layer to suit the amount of watering and fertilising - my use of liquid fertilisers will alter this old advice as the soil won't clog up with organic debris. I have also read that some no longer bother with the drainage layer. I am still going with a layer of coarse baked clay on the bottom of all my pots.

Its pot was well shaped internally and after the wire was removed it came out very easily. The condition of the roots on the sides of the pot were not brilliant. This maple had been standing outside in the winter with no protection from frost or rain so this may be the norm.


This one was grown over a coarse drainage layer of Biosorb. The two distinctly different substrates made it easy to cut back the base of the roots to just below their old level.


Once the roots were out of the pot they were untangled and combed out - any crossing or thick roots were trimmed back( there were not many of these ). The roots were now in good condition as they are already been straightened out from previous repottings and were radiating out evenly. A few new surface roots were running circles around the trunk and were removed. The tree had been in this soil for 2 years and was ready for a trim. I did clean the bottom of the root ball as well - happily there was not much there other than lots of fine roots.

Most of the old soil is removed. This was 2 line Akadama after 2 years outdoors - I saw very little degradation of it.


This maple is now coming into its 7th year with me. The trunk is 6cm thick and the roots above ground at 12cm. It is starting to look very attractive. It is also developing a rather nice bark.


I am gradually moving away from Akadama so this is about 50% Akadama and 50% Fuji volcanic grit. I am only using Fuji volcanic grit because its what I have on hand that won't degrade - any other hard modern substrate will suffice. All the substrate is mesh graded and dust free. In addition I have added a large helping of rootgrow to help it along. I have found that this gives the maples a good deal of extra energy.

I will continue to grow these with Canna nutrients. This year I will use the Hydro Vega product which is for run to waste hydroponic systems using inert substrates ( basically what I'm doing with bonsai ). I did also apply Rhizotonic to when I gave it its first watering to help the new roots along.

The first leaves are out ( repotting timed perfectly ) and I expect the maples to be in full leaf by in another few weeks.





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