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Writer's picturebonsaisouthwest

HOW TO THICKEN AZALEA TRUNKS

This technique is for creating a tree of around 40-50cm tall.


This method starts with a healthy young azalea (like those in the picture below) that has had side shoots nipped off and has had the first wiring applied in order to get the first bends into the lower trunk.


If you want to make a taller tree of perhaps 75-100cm you will have to continue growing the young azalea until the desired height is reached. Do that by reducing the apical shoots to just the central shoot. Leave the leaves on the stem wherever possible (Right side) because these will be the food factories while the whip grows. If you remove these leaves it will take much longer to grow the plant to a good height.


Once you have made all the bends you want while the trunk is thin and the tree is at the height you want it is time to start thickening that trunk.

Of course this process will not happen overnight but if you follow some simple steps a large trunk perhaps as thick as 2+ inches can be achieved in a relatively short 10 years.

This may seem a forever time span but as the years go by and the progress is seen you will soon have a tree that is showing the majestic trunk so desired by many.


The first thing to remember is to keep your tree growing at quite a fast rate and resist the temptation to prune it. Pruning will slow the growth rate dramatically and add years to the development timescale.


This requires a slightly different fertilising and pruning method than you would employ on more finished material.


In order to promote the fast growing 'water sprouts' you will only prune the tree once each year in winter around December to January.

Repotting will be kept to a minimum because each time you repot the tree you will cause it to put all of its energy into repairing the roots.

Removing flower buds to preserve energy will not really be necessary because of the type of pruning you will be doing.


Showing the fast growing 'water sprout' growth.


It is important that you should by now be familiar with the two types of shoots that azaleas produce. One is short and slow growing and the other is a fast growing shoot called a 'water sprout' that will grow very straight and may reach over 12 inches in length in one season.

It is of course these strong straight shoots that we will be encouraging to do the job of thickening the trunk. These water sprouts will be selected and pruned every two years and not on the yearly basis that you might expect.



Here are a couple of great videos by a Japanese azalea grower which shows the techniques that are outlined here on a massive satsuki. The first deals with the pruning and the second shows repotting.


Prepare by gathering together the relevant materials.

  • A suitable container like wooden box made for the purpose or a polystyrene box that is at least 4 inches deep but not too deep. Six inches deep would be more than enough at this stage. These will provide a warm growing environment for the roots that is less reactive to changes in the temperature. Failing this you can of course use a plant pot or similar.


  • Good quality growing medium, Kanuma soil in grades from chunky 12mm plus granules to 3mm.

  • I have been using the Robert Callaham azalea soil mix (Far right) of 2 parts Melcourt propagating bark : 1 part pumice or Ezo grit : 1 part course perlite : 1 part kanuma. It will provide an open textured free draining medium for good root production.

  • Pot mesh for the holes in the pots or boxes.

  • Wire for securing the tree into the pot and for further wiring of branches later on.

  • Fertiliser. Practically any good slow release ericaceous fertiliser will be ok. Bio-Gold is great but you will need a lot of it and it will need replacing at 5-8 week intervals so it can work out quite expensive. Miracle-Gro continuous release for azaleas is a good fertiliser and only needs topping up every 6 months. Sierrablen (aka, Enmag) is an excellent fertiliser that lasts for nine months.

  • Seaweed extract or Rhizotonic are not fertilisers but can also be used regularly to enhance the health of the soil environment and tree.



STAGE ONE (First year) - Potting up

During the spring season, transfer your chosen tree to a spacious wooden or polystyrene container. To accommodate a plant the size of a 3-inch pot in this example, the internal dimensions should be around 6 inches (15cm) wide and a minimum of 4 inches (10cm) deep for the initial season. Larger dimensions may not be beneficial and could lead to root rot if watering is not managed correctly.

  • Prepare your chosen container by covering the holes with bonsai pot mesh and place a piece of wire to tie the young plant into the planter to make sure it doesn't blow around in the wind.

  • Sieve your chosen soil to remove any particles smaller than 2mm. Use a layer of larger particles at the bottom of the pot to help with drainage followed by the smaller particle sizes for the remaining space.

  • Spread the roots out so they are in a good position to form a wide nebari. If you don't do this you will end up with a tree that exposes its upper roots and would be better off as an exposed root style. (That's a different method which I won't cover here).

  • Ensure good, firm contact between the soil and the roots of the tree by working it in with a sharp chopstick.

  • Make sure the soil is firm but not compacted.

  • Do not compact the soil too much.

  • Don't mound the soil up too much in the middle of the pot or plant the tree too high in the pot as that can cause the core (shin) of the root ball to become dry and difficult to water in later stages. It will also hinder the production of a wide nebari.

The surface roots should be covered and the soil level should be level with the edge of the planter or ideally, a little below the rim to ensure water doesn't just flow over the edge when watering.


STAGE TWO (First year) - Let it Grow!!

Keep the tree growing fast by fertilising well and being attentive to watering needs.

If the tree dries out at any stage, the vigour will be lost and the length of time for the project will increase dramatically perhaps even by years.

During the sunny days of spring around April and May, place the tree outside in an airy position, in full sunlight and remember to turn the tree around by 180 degrees on a regular basis. This turning will help to keep all sides of the tree healthy and the roots will grow more evenly too.

Keep the nebari covered at all times. If you try to expose the nebari too soon it will never develop properly. Be sure to keep it covered by about 1cm-1.5cm of soil.


If the tree has some flowers on it now is the time to just enjoy them.

On varieties that have multiple flower types and colours, it is a good time to start labelling the different colours that need to be kept.

On varieties such as Kanuma-no-Kagayaki, Asuka and Aozora for instance, any branches with white flowers that show the slightest touch of red should be kept so, mark them with a piece of coloured wire and be sure not to cut them off by accident.

Mark other flower varieties with different colour codes of wire and keep a note of what is what in a notebook.

I use telephone wires as there are lots of different colours of wires that are great for coding branches. (red and white stripes for red and white striped flowers and so on.)

Doing this will give the best chance of the finished tree having all or at least most of the different flower patterns for the variety.


As the days get warmer during the summer June, July and August, keep an eye on the thermometer. If the temperature gets to around 20-22C place the tree in a cooler spot with more shade.

When the summer sun arrives it will be necessary to provide good shade and cooler conditions for the tree so that the sun does not cook your plants.

Avoid placing your tree on metal, stone or concrete surfaces because these surfaces get very hot in the sun and can cook the roots of plants that are placed on them.

  • Azaleas have very thin bark and over exposure to the very hot sun can be very detrimental to the health of the tree. It can kill strips of the bark and may even kill the entire tree.

  • Water will be critical during these warmer months so be sure to keep up with it.

A regular drenching will be needed probably every day or even twice a day during the hotter periods.

It would even be wise to dunk water your plants to ensure that every part of the rootball is receiving water. Failure to make sure water gets to the core of the roots will usually result in the apex of the tree dying off.


Keep it growing!!!

Apply more fertilisers if needed and continue with diligent watering.


STAGE THREE (First year) - Pruning

After flowering, remove any dead flowers as usual making sure to remove the pistils to prevent seed production.

Don't be tempted to do any pruning yet. If you do prune it at this stage, the tree will use energy to produce back budding and the growth rate will slow down on the rest of the branches.

Wait for a month (July, August) until there is a clear distinction between strong and weak shoots. When you can see clearly which new shoots are the strongest you can thin the weak ones out and leave 3 or 4 of the stronger ones on the ends of the branches. This will focus energy to those remaining shoots and they will grow strongly thereby thickening the trunk and base of the branches.


Don't prune anything else in the first year.


SECOND YEAR.

There won't be much to do in the second year except to continue encouraging strong growth.

The end of December to January will be the time to prune all that hard earned growth back. Just keep feeding and watering and protecting from strong sunshine.

Watch as the new growth starts to expand through the growing season and when the time comes to prune in the winter, don't be nervous.

The whole idea is to selectively reduce the number of shoots and branches so that the tree will produce stronger growing branches in the following growing season. It is this stronger growth that will fatten the trunk and begin to provide structure for future branches.

If you leave too many shoots the trees growth will slow down as it tries to grow foliage on so many shoots and the trunk will not thicken as quickly.

In December, begin by removing the obvious weaker shoots that will not be needed in future. Anything growing directly upwards and downwards and any that are growing backwards towards the trunk can be removed completely. Do not prune the water shoots that are growing strongly.


Continue to wire any branches that need to be shaped or where extensions to the height are required while they are thin and easily bent. Be careful as these tender shoots are delicate and will break quite easily.



THIRD YEAR.

In this third year you will concentrate on growing the strong shoots again.

At this stage, it may be necessary for you to pot the tree into a larger container. Do this in the spring season and again do not over pot it.

Give the outer roots a little tickle to encourage them to grow outward but without doing any root pruning, move the tree up to a pot size that is just a couple of inches larger. Again make sure that the nebari remains well covered.


In the spring and summer, don't prune anything at all during the growing season.

When winter arrives (around December), follow the same rough selection process from the previous year.


Removing the obvious weaker shoots that will not be needed in future. Anything growing directly upwards and downwards and any that are growing backwards towards the trunk can be removed completely.


Now, on the remaining branches which should be your thickening water shoots, shorten them to the leave the two branchlets nearest the trunk. Then reduce the shoots near the ends to just the three of the strongest shoots.


In cases where there is no bifurcation, cut them back fairly short and seal all the cuts. Sealing cuts is important to prevent sap withdrawal and dieback.


Wire any branches that needs to be shaped before the spring growth begins. Don't forget to keep an eye on the wire. Leave it on as long as possible in order to set the shape and remove it before it bites in too deeply.


From now on you will repeat the process of growing on fast for two years and then cutting back in the winter until your tree has reached the desired dimensions.


If you have any further questions please just get in touch and ask.

(pictures of the subject will help.)


Happy bonsaiing

Fred

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4件のコメント


Michaela Morton
Michaela Morton
7月05日

Brilliant information as always. Thank you Fred.

In the videos they remove any shoots along the branch length leaving a few strong shoots at the end to pull the sap along the branch. Is this something you would recommend?

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Of course, that's absolutely fine with me.

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