Juniperus chinensis var sargentii seems to be the accepted name for this plant however it also has the features of a sub-species if you compare it to the common Chinese juniper which is often planted around temples in China. This is a very large straight trunked and upright tree.
As we know, shimpaku has a completely different habit.
The name ”shimpaku” was given to the plant in the late 1800’s. It is found growing naturally in Korea, Taiwan, Japan and probably parts of China, however it was the Japanese bonsai enthusiasts who recognized it’s ornamental value and lifted it’s standing to an almost legendary status.
The habitat of shimpaku is/was the high altitude limestone cliff faces where collecting specimens in the early days of it’s cultivated history was an extremely hazardous activity. Collecting shimpaku has now been banned as the lucrative activity lead to it’s near extinction from many of these areas. Here in in it’s montane home it is subjected to constant air movement, common storms, landslides and daily mists and fog. It’s roots penetrate deeply into the cracks and fissures of the bare rock where they find a rather meagre source of nutrients and a low but constant supply of moisture.
Cultivation.
From the habitat description we can find clues about how we should treat this plant in cultivation. Although it’s rather adaptable, it is worthwhile keeping in mind some of the following points to help us avoid possible problems in cultivation.
Substrate..
Japanese authors recommend potting mixes which contain a large proportion of sand, and from my own experience, there is no doubt that the best root growth I have obtained was by using a mix of seventy percent quartz sand and thirty percent sifted clay soil. If Akadama is available to you, I would suggest using that combined with about fifty percent clean quartz sand of about 2 to 4mm particle size. Other successful combinations might be a hard diatomite, sand and fine bark or a mix containing a large proportion of pumice or perhaps even scoria might work well.
Whatever the mix, observe the health of the roots after a year in any new mix to determine it’s suitability and make adjustments if necessary, remembering that it is almost always better to use a fast drying mix and water more often that to use a mix which holds a water for long periods of time. This becomes apparent to us during periods of prolonged rainfall, during which, the roots of the tree may not have access to enough oxygen in it’s water logged potting mix.
Given it’s limestone habitat, a neutral pH (pH7) should probably be aimed at. Adjustments being made by additions of garden lime if the mix pH is lower than about 6.5.
Water..
When the Japanese say ”water mainly the leaves”, We should understand this to mean that constant flooding of the roots is unnecessary with this plant and also that these junipers dislike dry air and appreciate a daily hosing down or misting of the foliage without necessarily watering the roots. If there is moisture in the root ball, it is enough. A dry root system is of course to be avoided always. Also, consider using a substantial aeration layer at the bottom of the pot before adding your planting mix. This ensures that the roots deep down in the container always have good access to air until the next repotting period arrives, This layer has nothing to do with improving drainage as is often mistakenly believed.
Fertilizer..
Shimpaku can accept quite a lot of fertilizer but do not actually need it to thrive. So, at least after the tree is well advanced – perhaps ten or fifteen years – it may be well to reduce the rate of fertilizer to about one third normally given to vigorous deciduous trees for example. As always, fertilizing potted plants is easier when we use some kind of slow release food rather than a liquid alone. Mild, home made organic cakes being the first choice, followed by one of the manufactured controlled release products such as Osmocote or Nutricote but keep in mind the generally high nitrogen content of these products. Liquid feeding can be used as a boost if desired. If you are set on using diluted liquids alone, you will need to apply them each week or preferably, in lower doses, twice weekly.
Pots..
The choice of a pot is naturally a personal matter but it’s worth noting that giving too much room for the roots of any tree, and especially shimpaku, can lead to various problems such as unused mix becoming ”soured” or holding on to water for too long. Roots perform best when we allow the mix to dry somewhat between waterings so by using a well drained mix and a smallish pot, we will be free to water daily without worrying about over watering. If you intend to repot every two or three years – which you should – it is quite acceptable to allow no more than about 40 or 50 mm of room for new root growth between the outer edge of the trimmed root ball and the inner edges of the container.
Very shallow pots are generally unsuitable for shimpaku.
Training..
It is beyond the scope of this short article to go into the details of appropriate styles for shimpaku but as far as training and preparing young material for future bonsai use, there are a few points to bare in mind.
- The ”essence” of shimpaku is it’s wild and twisted ”free” form which does generally not conform to common lowland tree forms. Therefore, the sooner we manipulate the material the better. It is already becoming difficult to create strong bends into pencil-thick stems. Best results are obtained when using rather thinner material, so start your wiring when the stem you intend to shape is about 3 or 4 mm in diameter.
- The wood fibres of shimpaku spiral clockwise up the stems so we should endeavour to apply our wire following this pattern. Particularly on the main trunk and branches we should apply our wire in clockwise coils. The reason for this is that we can introduce strong twists into out trees which will become a very attractive feature when we later introduce shari and other dead-wood elements into our bonsai. We will then be able to recognize and follow the spirals around the trees as we remove the strips of bark and this will lead to a more authentic looking work.
Apply the wire rather loosely and twist the stem clockwise as you bend it. Be careful not to over do it and split the young stems, but shimpaku branches can take quite a lot of twisting and bending. This twisting also helps with our bending as the stresses of the bend are spread over a greater area than purely at the bend site. - Don’t forget the taper! This is a very important and often overlooked point in training in the rush for a finished tree. In all trees taper is created by leader replacement in both the trunk and branches. The procedure is as follows..
When wiring the branch or trunk, you must retain a side branch, somewhere along the wired stem, in reserve. This will be your new leader. After the wired branch is set into position and during the next wiring season, (usually autumn/winter) you cut the previously wired branch down to the replacement side shoot and continue your re-wiring up onto it. By doing this you have replaced the tip of the branch with a thinner section. Repeating this process for however long it takes until you are satisfied, will create the taper you need in the branches and trunks. The more frequent the leader replacement, the greater the amount of taper you will end up with. Obviously with shimpaku, we should probably not take this too far. A smooth gradual taper is best for this species.
In the mean time, as many lower branches should be retained as possible. This will help with both the thickening rate at this point and the overall taper of the stem. The lower branches may in turn be wired and twisted and later converted into jin or if low enough on the trunk, perhaps a second or third trunk line could be considered.
General care and maintenance.
The vigour and strength of shimpaku resides in the long extending shoots. Whenever these shoots are pruned, growth is stopped at that point for a long period of time. If we cut all these shoots off, the entire tree’s growth is halted until it slowly produces more extensions. We can use this habit to our advantage when we need to slow down or encourage growth in a particular area. For example, we might use this technique to help in regulating the taper of the tree’s trunk or branches.
When we are satisfied with the overall structure of the tree, we need to start the pinching process. This will cause the energy which was previously concentrated on one ore too long shoots to be re-distributed over many shoots and after repeating this over a number of years we will end up with the beautiful rounded clouds of foliage which are such a feature of mature junipers. Pinching involved removing and soft shoots which extend out past the desired profile of the foliage mass. It is to be done with the finger tips not the finger nails.
Of course the work does not end there. Overly dense areas will need periodic thinning out so as to allow the penetration of light into the interior of the foliage masses. If this is neglected there will come a time when the small interior shoots begin to die off leaving leaves only at the very tips of the branches. This needs to be avoided at all costs. When thinning out, use a long handled pair of sheers to remove entire small shoots from their bases. Repeat until you can see the stems of inner smaller branchlets and then stop and let the tree grow again. The thinning should be performed every year or two. Pinching however is an on going process.
Shimpaku should be positioned where it receives full sunlight for the greater part of the day. It is also important to remember to periodically turn your trees around so that all areas of the tree get their share of full light. Failure to do this will end with an unbalanced tree with a strong healthy front and a weak back part. Shade should given during extended heat waves and especially during periods of low humidity. At these times, place your shimpaku where it receives no more than about an hour of full sunlight in the morning or very late evening or place it under 50% shade cloth. Give a refreshing shower of water late each day when the weather is hot and dry.
Various junipers including shimpaku are sometimes attacked by a species of large black aphids, small whitish scales or various mites. This happens more often when the trees are overly protected and sheltered away from wind and rain and also when they are in an unhealthy state due to lack of repotting or starving from an exhausted soil. Mites and aphids are easily controlled by removing the tree to a more exposed position and spraying a couple of times with soapy water. Scale insects usually call for systemic insecticides or some kind of oil spray. Be warned that spraying junipers with oil results in their glaucous waxy coverings to become impregnated with the oil and turn green. This however does not seem to endanger the tree itself and the new growth will again be the original colour of the species.
Propagation.
Propagate shimpaku by taking rather long cuttings (about 150mm) with a heal torn from it’s parent branch. The cuttings are stripped of their lower leaves, the heals are neatly trimmed and the cuttings are then inserted into a sharp sand or sand/peat medium. Cuttings are usually taken in late winter or late summer. The cuttings are placed in semi shade for a few weeks and gradually introduced into full sunlight. It is the light more than anything else which stimulates rooting. Leave the cuttings in the container until the following spring when they are potted singly. Shimpaku is also easily air-layered using the wire tourniquet method. You can use this opportunity to make multi trunk trees. Air layering can be performed most times of the year. Most varieties of juniper are treated similarly.
Varieties.
Kishu.
This is the most commonly available variety and is known in the nursery trade here simply as ”Shimpaku”. It has lovely dark green foliage and a rather dense and course growth. It is slow growing.
Itoigawa.
A highly revered ”variety” and the most popular in Japan. It was originally found growing in the Itoigawa district inJapan. Probably not a true botanical variety but more a form of Shimpaku selected from the mountains in this area. It will become more available in Australia in the future. It’s foliage is very fine and a more yellowish green when compared to Kishu. It is more likely to develop the scale type of foliage when overly disturbed. It is a fast grower.
Blaauw
This is also a Japanese selection which was named after a Dutch nursery when introduced into Europe. It is included in the same group as other shimpaku varieties, has a similar habit and is probably from similar areas originally. It has a distinctly bluish foliage colour mid-way between Itoigawa and Kishu. It is also a fast grower – for a juniper.
Take home points..
Shimpaku is a classic bonsai subject and suits any size of bonsai.
It is easy to grow and look after if you follow the basic requirements.
It is essentially a mountain plant and appreciates cool moist conditions. Especially moist air.
It will respond to quite high daytime temperatures with faster growth.
Be patient with it, it is slow to thicken but becomes more beautiful with each passing year.
Create jin and shari on it’s trunk and branches to give it the wild look.
Use deeper rather than very shallow containers.
Think about some new and interesting styles and try not to just copy what you have seen before.
Disinfect cutting tools between trees by dipping in alcohol.
wire the branches with clockwise coils.
Pinch the tree whenever necessary.
Shimpaku is a special plant – Enjoy it!