Frosty nights and mornings

I hope the latest spate of frosty nights and mornings has not interfered too much with your re potting attempts. From the way my stocks of Akadama and pumice etc have gone down, I guess you are all busy at the moment.
As someone who re pots a lot of trees every year, both for myself, clients and students. I still get quite surprised by the lack of knowledge surrounding the correct procedure of re potting bonsai and also material trees including yamadori. Some people think think re potting is simply replenishing the potting medium and cutting roots off. If only it was so simple.

Here is a classic example of what you should see when you come to re pot your tree. In this case, it's a Trident Maple Acer buergerianum, which was re potted only 2 years ago.
This picture also illustrates what you should be aiming to achieve with the root systems of your trees after re potting.
I have seen instances with other trees that were also as vigorous as the tree in this image. That when planted in pots with an internal over hanging lip/rim that restricted the expansion of the root ball, simply split the pot. This scenario often happens when people do not listen to their trees. Rather, they rely on some text in a book or magazine which tells them to repot their tree every 5 years or 7 years etc. Instead of being guided by the requirements of each individual tree. But it does illustrate a trees power even if it is only small.

In this next image on the right, you can see all the fibrous roots. It is these capillaries that do all the work. You will notice that there are no big heave roots visible in either picture. They are merely for stability. In a pot environment they are redundant as we tie our trees into the pot to give stability until the root ball has re established enough to hold the tree securely. It is the thin little guys that you have to grow when you have a tree in a pot. These are the ones that your tree needs for healthy growth. Ideally we want over time, to fill the pot with these roots like we can see in the first picture at the top.

So what is it that gives us these capillary roots we desire.

There is a clue in this picture below.

This is a tree I received recently. Notice it is planted in what can only be described as 'building site rubble'. Compare that to the mix that is in my hand. Any ideas yet?

If you think that trees should be planted in a fine mix to generate fine roots then give yourself a pat on the back. Using big particles like you see in the pot here, will not generate a plethora of fine roots. Yes you may have some fine roots but not in the numbers to grow a bonsai at it's full potential, but you will also get big coarse roots

The only time you should use larger particles is for drainage, this is especially so in cascade pots.

A word of warning here. Be careful of some of the cheap Chinese pots (any design) that can have the bottom of the pot raised up like a souffle. Or conversely sagging, which can lead to standing water in the pot, either around the periphery or in the middle dependant on the position of drainage or tying in holes. It is even more important to have a drainage course if your pot is like this to avoid root rot. And I would recommend pumice or similar for drainage. As a bonsai professional I get through a lot of cheap pots when establishing yamadori and I see these misshapen pots a lot.

You might think that a tree a metre tall would have roots bigger than a tree 12 centimetres tall. But you would be wrong, capillary roots are capillary roots. I am talking here of trees of the same species. Of course there are some species with finer capillary roots than others and vise versa. But you still need a small particle mix to generate small roots. 2-5 ml particle size is the maximum I ever use. Obviously with shohin I use the smaller particles so as to be able to have as much root as possible in a small container.
I am sure many of you will have heard of the guy who can get 7 different sizes of Akadama from one bag. !!
With yamadori or any trees collected with long roots, that only have capillary roots at the tips. It becomes your mission to develop as many capillaries close to the buttress of the tree as possible. We want to have the fine feeder roots starting as close to the trunk as possible and filling the pot. If the feeder roots start a long way from the nebari on long roots we will never have the best root mass to pot area that we could. Over time we want to reduce the length and size of the big roots that provide stability for roots that do the work for the tree. I once spent 8 years compacting the roots on a Common Juniper Juniperus communis, that arrived in a box the shape of a coffin. Eventually it was potted into a square pot that was 25% of it's original length. Of course there are short cuts, like grafting on new roots closer to the trunk, however the horticultural challenge to move the roots by growing is more difficult and a good skill to master. This is made so much easier by having the right particle size for your mix.
Of coarse the actual mix is important too. If you ask two people what is the best mix you will get ten different answers. There is not any single mix that fits all. But there are some NO NO's. I am sure everyone recognises that the UK is generally a wetter place than it is drier. So from that, without the help of Poirot, Miss Marple or Sherlock Holmes it is easy to deduce that anything in our mix that hangs onto water is not good. So please please no more John Innes!! It is like blotting paper. And remember, it is easier to add water than take it out. FACT!

Just a few tips.
Beware of using collected organic components like leaf mould or needle litter for your mixes even if they have been recommended by your guru. This is one of the quickest ways to introduce disease into your pot.
AKADAMA, KIRYUZUNA, PUMICE, KYODAMA, KANUMA, MOLER etc etc. You are probably all familiar with these names. And there were many others I could have included. They are all well used and tested mediums that combined in different ratios give us the mix we use for potting our trees. One of the good things about using these inert products for your potting mix is that they contain no pre added unseen fertiliser, no water, no disease. You are starting off with a level playing field. Therefore what ever goes into the pot be it fertiliser, water, etc is what you add.

When raking out roots be careful when using root rakes or root hooks which can be very damaging if not used carefully. Remember Captain Hook did not always have an eye missing!
Sometimes when I am working on teasing out roots I will use two chop sticks in one hand held with a light grip. If I hit anything that has a bit of resistance the chopsticks will flex out of my grip. If you go bull at a gate with a root hook and meet resistance, the hook always wins leading to roots being ripped out. What I guess I am trying to say here is your trees are living things. Treat them gently but more importantly treat them with respect.

When you tie in your trees do not use copper wire. It will make your trees sick and weak over time. Use aluminium or steal but not copper. Junipers in particular go a bit sad from this.
When you have tied in your tree if you resort to twisting the wire UNDERNEATH the pot, then you have not tied it in properly in the first place. Learn the correct technique.

With almost all deciduous trees we want a nice flared nebari. This only comes from lateral expansion of the root ball which flutes the trunk base as it flares out. By putting trees in overly deep pots or pots which restrict lateral extension in the roots we are slowing down greatly the chances of developing a good nebari.

Try using some of the modern products that encourage root regeneration after potting/collecting. Use Vitamin B1 for stressed trees! All living things benefit from B1.

Often when trees arrive from Japan, they are pot bound. Very difficult to water and lacking vigour. Because I cannot repot the tree in June/July after quarantine finishes I use enzymes which break down all the dead root in the pot turning them to valuable sugars that can feed the tree. This in turn opens up the rootball so that I can water and supplement the tree until it is the correct time to repot for that tree. The use of this modern product not only helps the tree but it buys me valuable time.

I have not gone into great detail into how I re pot, if you want that then you need to come to me. I am just trying to stimulate a little bit of thought in those who just go through the motions never thinking about what they are doing or why they are doing it. And not thinking about the tree. And if you ever do a workshop with me or see me do a demo you will know that the tree comes first!

And finally, is Spring on the way?