Chinese Scale Juniper Bonsai

In this article I will try to explain the pruning and maintenance of scale foliaged Junipers such as, Juniperus Chinensis ‘Sargentii’ and Juniperus Chinensis x Media ‘Blaauw’.  These varieties are very popular for Bonsai due to their excellent tight compact growth, to create nice tight foliage pads, as well as being quite prolific in back budding once they are pruned correctly.  The natural habit of these species grows in a columnar form with dominant ascending branches, so it produces good low sacrificial branches to make the trunk thicken.  These sacrificial branches should be thinned out to varying heights on the trunk, because the trunk can get inverse tapered if too many branches emerge from one point.


In Britain with our variable climate it is important to monitor the trees active growth for the timing of which this task is undertaken.  It is advisable not to pinch back the growth until at least a month after visible growth extensions have appeared.  This is usually around the month of May, then this pinching can be continued on until August, but it is advisable not to pinch continually without a break for growth extensions because the new growth on Junipers takes in far more goodness than the existing foliage.  You should pinch with your finger and thumb to pluck the growth tips because this will break the shoot at its weakest membrane, reducing die back.  This is the main reason why you shouldn’t use your fingernails when doing this task.
To balance the energy of growth within your foliage pads you should pinch more strongly around the dominant area of the pad.

As you can see in this diagram below the energy is dispersed to the weaker inner growth shoots.


When pruning this species it is important to cut back to a secondary side shoot when reducing the growth extension.  You should cut along the central section of the shoot with sharp scissors remembering NOT to sever across the green foliage, as this will cause browning.

This species can get very dense around the apex of the tree where it gets maximum sunlight.  So, for specimen Bonsai you should thin out during the summer months around the crown to allow light to enter to the lower branches.  You should do this by plucking between the shoots and thinning around their junctions.  If this is not done this species will naturally thin itself more heavily – this is called June fall, which is the yellowing and dropping of old inner growth.
When hard pruning has been done you can sometimes get reverted juvenile needled growth.  This is nothing to be concerned about; this will soon change into the adult scaled foliage once it has matured.



In Japan the Scale Juniper grows far faster than in this country.  This is mainly due to Japan’s much higher humidity.  I have found the biggest problem is transpiration (moisture loss from the foliage due to sunlight) through its foliage.  Therefore I have found this species puts on more growth extensions in a shadier area, rather than full sun, so I would recommend this positioning if major styling has been done to the tree.



This tree can be wired throughout the year.  It will have more suppleness in the branches during active growth, therefore if you need to move large branches do so accordingly.
In Japan, on their very old specimen Juniper Bonsai, they bind the branches tightly with wet raffia to prevent the branches from snapping off.  This acts as a protective membrane causing small stress fractures rather than one big break and, also stops moisture loss from the cracks within the branch.


You should fertilise with a slow release feed such as the rapeseed cakes from full active growth, April-May until September.  You can apply quite liberally providing the tree is healthy but, be careful with soluble buffer feeds that are high in Potassium, which will cause berries to form making the tree to lose energy.  If this does happen you should remove the berries immediately by simply rubbing them off.   I use Miracid Soluble Acidifier on top of my organic slow release feed in the spring to neutralise the Ph and this contains trace elements for the tree to absorb.  This is particularly helpful if the tree’s foliage has been tainted by the frost because it helps the tree green up quicker.



This species has a woody root system, so it is very susceptible to root rot.  It also hates salts that can come from unwashed grit, so you must always make sure the aggregate you use is for horticultural use or thoroughly washed before using it.   I use a very free draining soil mix of sifted and graded 70% double red line (hard) Akadama free from dust, with the larger grades at the bottom and, 30% Japanese Kiryu soil, which works very well with Juniper roots. If your Bonsai container does not have many good drainage holes or it is a plastic pot, you will need to add more of the Kiryu drainage medium, so the water can flush through quicker.


When watering you should monitor the soil to make sure it drains quickly.  If not, be careful during the winter period by protecting from rain and frost.  This tree does like to be regularly watered but not to sit in it, so the fine Akadama top dressing should indicate when the tree is coming up to watering.  The foliage should be misted when watered, which will clean the dust off its pores; the only problem with this is that it encourages algae on the trunk and branches that you will have to clean off.



There are two main pest problems on Scale Juniper.  The first is Conifer Mite which is very similar to red spider mite.  It has the same symptoms of patchy yellowing and fine cobwebs.  This can be cured with most insecticides such as Provado Systemic Insecticide made by Bio.  The second main pest problem is Juniper scale which can also be treated with a systemic insecticide.



This tree is quite hardy outside in Britain providing the soil is warm and free draining; in an Akadama soil based mix.  The only problem with the frost is that it taints the foliage colour grey, so it can take a longer time to put on growth extensions in the spring due to waiting for the old foliage to green-up.