Old, Imported Japanese Black Pine gets a repot

Background

This Japanese black pine comes from Aichi-En nursery in Japan. It belonged to my teacher, Mr Junichiro Tanaka until I bought it as a birthday present to myself last year.

Image caption. Nice birthday present right?

It had at some point suffered a bad spider mite infestation and the tree was weakened by it. It also caused all the needles to become a rather pale yellowish green.

Needless to say, I have not done anything to it as whenever working on a tree its survival of the technique outweighs all else. So if the tree you plan to work on is not strong to begin with, you are likely to weaken it further by stressing it through wiring, defoliation or other such techniques.

Some attractive features of this tree

I love powerful trees. I guess this is why I love Japanese black pine so much, for me they project loads of power and have a real presence when on display. When walking through the nursery and Mr Tanaka indicated he would sell this tree to me I was immediately enthralled by it.

1. It has amazing movement; apparently it is a yamadori.
2. The amazing shari detail on the tree is natural and very weathered.
3. The extremely thick bark plates provide clues as to just how old this tree might be. The nebari is also rather interesting, which often is not the case with pines.

Image caption. Close up detail of the bark character

Image caption. There is a lot of natural, weathered shari on this tree. In the future I hope to restyle the tree, changing the planting angle slightly to display it better.

Image caption. Close up of the roots on this Japanese black pine. Its a very interesting coiled affair; the roots must have been exposed many years ago for them to have developed this amount of mature bark.

Current state of health

Image caption. Spring candles

With liberal applications of BonsaiBoost, last growing season especially in Autumn, the tree has gathered sufficient strength to push out a lot of strong, spring candles. This is a very good sign.

Image caption. The balance of energy of this tree must be restored

The energy in this tree is completely out of balance and in time it will need to be restored through needle plucking and decandling techniques.

Decisions

Akadama and pumice (Japanese hyuga), the medium which this tree is planted into will begin to break down after some years. Many people see this as a negative but in fact it is not. When you repot a tree you remove much of its roots, so in the weeks and months afterwards, you want the tree to issue new roots so it can support the canopy. However after a few years you don't still want this strong growth to continue as it becomes too difficult to manage the tree and prevent branches from become coarse and essentially losing ramification.

If using Akadama the particles do begin to break down as fine roots are able to penetrate and split them and in so doing will reduce drainage. This results in increased water retention. Both these factors result in retarding the growth of the tree.

In this trees case, the akadama has broken down to some degree and ordinarily I would leave the tree undisturbed for another year or more however before I can work on the tree I need it stronger. So the best thing for it will be to remove the old soil and repot it using a very free draining, drier mix. In this case it will consist of akadama, pumice and LECA in equal proportions. If I were repotting a healthy tree where development was almost complete then I would have used 2 parts Akadama, one part pumice and one part LECA or crushed stone.

Preparing the tree

The copper wire which had been used to style the tree a couple years ago was still on the branches. If the tree is to be placed in a free draining mix in order to promote rapid growth, I don't want to incur too much wire bite or that it becomes so severe that it is actually a problem so I will need to remove the wire.

Image caption. Wire bite already visible on some of the branches.

Wire bite on young pines is actually a technique which sometimes can be used to promote thickening. The wired section will push out against the wire and in so doing will fatten. Of course there comes a point where this is excessive and the wire actually becomes lost in the bark. Ideally you want to avoid the latter situation from occurring.

Image caption. Cutting the copper wire with a bonsai wire cutter.

Fortunately a friend of mine, Andre de Kok was kind enough to assist me in removing all the wire from this tree. It is amazing how much wire a tree of this size and level of refinement can hold, and how much time is required to remove it.

It is best to cut wire where possible, into shorter sections which can then be easily removed. However when you find areas where the wire has bitten in, it is better to use a pair of pliers to carefully remove the wire by uncoiling it. It is thus best not to remove wire in the active growing season if at all possible, and if you must  preferably do so in the tail end of summer or better yet, in autumn. This is as the live tissue, the cambium can easily be separated from the hardwood beneath during the active growing periods. So when removing wire which has bitten in, the bark can also easily be lifted at the same time. When this happens it is best to immediately seal these areas with a good bonsai tree sealer to prevent as much sap/resin from leaking.

Image caption. Copper wire scrap

From an environmental consideration it is best not to simply discard of any old wire whether copper or aluminium. Rather separate it and collect it in containers. You can then take this to the recycle depot, and perhaps even get a few cents for it!

Image caption. Some branches had died and had to be removed. A root cutter which is a very strong and durable cutting tool is my tool of choice for such tasks.

Lifting the tree from the pot

Image caption. Using a repotting sickle makes it easier to lift a tree from its pot

A repotting sickle is used to create a small gap between the root ball and the container. This makes it possible to maneuver the tree from the ceramic container without breaking it the container or the root ball. When working with more valuable ceramics such as this one, you need to act with caution so as not to chip or scrape the pot with the sickle.

Image caption. Removing the tree

Gently but with deliberate action, I eased the tree out of the pot. When performing this step one needs to be very careful not to break off the bark. The bark which gives so much character to this tree, were it to be broken off, will take years to develop again.

Image caption. Healthy white root tips are confirmation that the tree is actively growing and confirming that my decision to repot now was spot on

Working the roots

Image caption. The root ball being raked

Starting on the underside of the root ball, the roots are raked to remove old growing media.

Image caption. Cutting thick roots which have developed too long

When you encounter a thick root which needs to be shortened the best tool for the job is an appropriately sized root cutter. We need to shorten these thick roots to promote a more fibrous root system with fewer storage roots and more feeder roots. It is these feeder roots which support the trees ramification.

Image caption. Cutting the roots with scissors

Thinner roots which have grown too long can be cut using a pair of scissors. I would recommend a heavier duty scissors for this task, something like what I call the general bonsai scissors. Delicate scissors like those used for trimming buds would not be appropriate as their blades are too delicate. Whichever scissors you use, don't use the same pair with which you cut branches. Scissors used where there is growing media present will be blunted and become damaged fairly quickly. For cutting branches you would want to use a tool which is sharp and will make clean cuts, which will heal over quickly.

Image caption. Using a pick to open the root ball

Raking the roots will invariably result in the loss of some roots. Therefore as you get nearer the size of root ball which you wish to retain you want to use a tool other than a rake to work with. At this time you are better off using an ice-pick or similar tool. I made something from an old screwdriver which I sharpened to a very blunt point using an angle grinder.

The idea is to gently ease the pick into the root ball and wiggle it a little to open it up. This action results in aerating the root ball which is critical to its long term health. Failure to perform this step will mean that near to the trunk the root ball will become more and more compacted. Fewer and fewer fine roots will survive and the only fibrous roots will be found at the edges of the root ball. However eventually you will need to cut back hard and then there will be no roots to cut back to and this is sure to weaken or even kill the tree. 

So working from the outer edge of the root ball you work inwards, gently pushing the blunt implement into the root ball. Sometimes you will encounter a root so try from a different angle. Don't be in a rush and jab the tool into the root ball as this will inflict damage on the thicker roots and may also break the thinner ones. This step does take time but when done properly the root ball should feel spongy. This now open structure will allow water to penetrate and drain easily and for vital oxygen to penetrate.

Image caption. The root work is now complete

Preparing the pot for planting

Image caption. After a quick clean with a soft bristle brush the drainage holes are covered with new mesh, which will prevent any loss of growing media.

Image caption. Drainage layer of medium sized pumice

Pumice is a great medium to use when you do want a drainage layer. It promotes rapid drainage, holds some water but also provides a unique, sandpaper-like surface over which roots seem to ramify readily.

Image caption. (Clockwise from top left) Leca for drainage but you can also use stone, medium sized pumice, medium sized akadama, fine akadama, fine pumice and carbon

The ideal 'moisture' scenario is one where the entire pot dries at roughly the same rate regardless of the zone (top or bottom). If the same medium is used with no change in particle size regardless of the zone, you will most likely find it dry on top and wet at the bottom. This means that in order to prevent the surface roots from drying out altogether you need to water again, but this means that the bottom zone never gets close to drying out. Some trees like the pines grow best when the roots are on the dry side. Maples for instance, in contrast, don't like to get too dry and should remain almost constantly on the wetter side of moist. It is for this reason that it is not as important a consideration to use varying particle size with deciduous trees as it is with conifers as "they don't like wet feet."

Image caption. The middle zone, medium sized Akadama and medium sized pumice

In the middle zone, or middle 1/3rd of the pot I have used a combination of medium sized Akadama and pumice. The Akadama at this point is intended to retain more moisture but yet provide excellent drainage and oxygen exchange.

Potting the tree

Image caption. When repotting stand back and confirm the planting angle

Having an extra pair of hands for this repotting was such a big help. Andre is seen above holding the tree in position so I could confirm the planting angle. Once you are happy then the tree's position can be fixed by using wire, inserted through the provided holes for the purpose in the pot or through the drainage holes.

Image caption. The top layer is made up of finer material

The finer (smaller than 6mm) grades of akadama and pumice were used for the top layer. Smaller particle sizes mean smaller gaps between particles but more storage capacity for moisture.

Be sure to work the growing media into all the cavities so that no large air pocket remain. In the image above you can see a blunt metal rod being used. You can pretty much use anything, I often take extra chopsticks when I get sushi and use those. Just make sure the tip is blunt so that no roots are impaled when you work the growing media in.

Watering and aftercare

Image caption. Watering in the tree with a fine spray wand

Once you are sure that you have worked in the soil properly the tree should be thoroughly watered. As the brand of Akadama that I sell is of high quality there is really very little dust but it is best to water until the water running from the drainage holes is as clear as it is directly from the tap.

Pines rely on sunlight reaching their needles in order to gain energy so it makes little sense in placing a recently repotting pine in shade for too long. This will only serve to weaken it. The biggest factor you should take precautions against is wind. Wind can unsettle the tree and create minute movements of the tree in the pot, this is why securely wiring it into the pot is so important. These movements may causing damage to young roots, depleting the trees energy resources even further. So place the tree in a sheltered, sunny position.

Akadama is great as it changes to a dark brown colour when wet and so it is quite easy to see when the tree requires watering again. It is important to allow the growing medium to dry out to some extent. Excessive water will retard the formation of feeder roots and instead result in sparse, coiling roots.

Fertilizer will be withheld for the first few weeks and then a few bags of BonsaiBoost will be added. When a tree is in a weakened state it is never a good idea to actively try to promote growth through fertilizing, rather respond to the trees growth by supporting it with fertilizer. Of course any fertilizer applied to a tree which has just been repotted and has few feeder roots with which to take up the nutrients will simply be wasted anyways.