Along with Pines and Japanese Maples, Junipers are one of the three most frequently used genera for bonsai. Juniperus is a genus of 50+ species of evergreen, coniferous shrubs from dry forests and hillsides throughout the world.
Junipers have foliage of two types, needle-like juvenile foliage and scale-like adult foliage, species that exhibit predominantly one or the other are used for bonsai cultivation. The range of colour of the foliage ranges from steely-blue-greens to light greens occasionally with silver or gold hues.
Most of the classic Juniper bonsai in Japan have been collected as yamadori from the mountains and can reach ages of 200 years or more. Many display large amounts of natural and artificially created deadwood called jins and sharis which are bleached brilliant white with lime-sulphur.
Species and varieties suitable for bonsai
The classic Juniper for bonsai is often referred to as the Chinese Juniper. This is a naturally occurring hybrid species called Juniperus x media which is a cross between J.chinensis and J.sabina. (Confusingly Juniperus x media is also referred to in some textbooks as Juniperus pfitzeriana).
The foliage can have a mixture of adult and juvenile foliage and as this combination can disrupt the design of a bonsai, so varieties of J.media that display only one form of foliage tend to be used. Juniperus x media ‘Blaauw’ (named by a Dutch nursery ‘Blaauw & co’) is a strong growing conifer which carries bluish grey-green scale-like adult foliage. As with other J. x media, if needle-like juvenile foliage appears it can be pinched out until adult foliage appears.
Another very popular species for bonsai is Juniperus rigida, the ‘Needle Juniper’. As the name suggests J. Rigida has sharply pointed needle foliage as has Juniperus communis a plant found growing wild in many parts of Europe, though it should be noted that collected J.communis is notoriously difficult to keep alive for more than 2 or 3 years after collection.
Juniperus squamata (needle foliage), J.sargentii (scale foliage), J.chinensis, J.Sabina, J.horizontalis procumbens, J.communis hornbrookii are also popularly used as are dozens of other species and varieties.
Other Juniper varieties often used for Bonsai
Shimpaku or J. sargentii
The Shimpaku is a Chinese Juniper variety with bright green new foliage that fades to a darker green when mature. The tree has naturally dense and compact foliage which is excellent for bonsai. As with a number of Juniper varieties, the foliage can turn a brown or bronze colour after frost and will remain so until Spring when it turns back to a more familiar (and healthy-looking) green.
Blaaws Juniper or J. x media ‘Blawii’
The Blaaws Juniper is more vigorous than the Shimpaku but has less naturally well-ramified growth. In comparison, the green foliage has a blue-grey tint.
Sabina Juniper or J. sabina
Common to Europe and similar in colour to the Shimpaku, the Sabina has looser but finer foliage that requires continual pruning of vigourous shoots to encourage ramification. Sabina collected in Northern Spain can be a difficult species to look over in Northern Europe. Although very frost hardy, they suffer very badly unless kept fairly dry during the Winter and the Summer.
San Jose Juniper or J. chinensis ‘San Jose’
A Juniper with blue-green foliage and beautiful red bark, more commonly found in the United States. The San Jose is reluctant to form uniformly adult/scale foliage and on occasions enthusiasts will opt to develop with juvenile/needle foliage only.
Blue-Rug Juniper, Creeping Juniper or J.horizontalis
A very common Juniper variety sold in garden centres and shopping malls across the world, J. horizontalis has very weak trunks and branches leading to a naturally horizontal, creeping growth habit. Predominantly mature/scale foliage in a range of colours from dark green to steel blue (depending on the specific variety). Trunks are very slow to thicken.
Himalayan Juniper or J. squamata
Very commonly found growing in European gardens and nurseries, J. squamata carries juvenile/needle foliage only in a wide variety of colours, depending on the variety. Very vigorous, fast growing and responsive to bonsai techniques but its appearance suffers from the retention of old needles that steadfastly remain on the tree after dying and browning off.
Common Juniper/J. Communis
J. communis is the only truly native Juniper in the UK. A needle juniper with dull-green foliage, the Common Juniper has a terrible reputation for dying inexplicably 2-3 years after collection however garden centre/nursery specimens appear to be far more robust.
BONSAI CULTIVATION NOTES
POSITION: Full sun though Junipers with predominately scale-like foliage benefit from a little shade from the midday sun. During winter protect during frosts below -10°C but coniferous trees should not be over wintered in dark outbuildings unless temperatures are consistently below -10°C, at this point there is no requirement for light.
Never try to grow Junipers indoors, though they may seem to tolerate indoor cultivation at first, poor humidity, lack of light and dormancy will eventually kill them. Do not trust a vendor, seller, book or website that claims Junipers can be grown successfully indoors. Dead Junipers can continue to display normal foliage colour for weeks or even months after they have died at the roots.
WATERING: Ensure Junipers growing in poor, compacted organic soils are not over watered as they suffer root rot easily.
FEEDING: Feed fortnightly; high nitrogen fertiliser from start of growth in Spring until mid-summer and a balanced feed until late summer until winter. Occasional replacement feeds with an acidic fertiliser such as Miracid are highly recommended, particularly in hard (lime) water areas.
Repot in August-September (late Summer/early Autumn), this is a much better window of opportunity than the more traditionally advised timing of late Spring. Autumn repotting takes advantage of the huge increase in root production after the growing season, whereas spring repotting will disrupt growth during the year.
Once established in a good quality soil, repot infrequently every 3-5 years. Never bare-root a Juniper or change more than a third of the soil (or at very most half) in any one repotting.
An inorganic-clay based soil is essential for Junipers as they are prone to very poor-health in old, compacted, organic soils. Because Junipers cannot be bare-rooted or have more than one third of the soil mass changed in one year, it is essential that a soil with good particle structure is used. Avoid using pure Akadama that break down after one to two years and will impede drainage until it can be removed.
The wood of Juniperus is extremely flexible and branches of several centimetres in diameter remain supple enough to be shaped with ease. Junipers can be wired at any time of the year including the semi-dormant period of Winter. Do not create heavy bends in trunks and branches during temperatures of 0ºC or less.
For a well-defined Juniper bonsai, the entire tree will require 100% wiring at least once in its lifetime.
The setting time for newly-wired branches depends on the thickness and the vigour of individual shoots; expect anything from 3 months to a year. The greater the amount of growth that emerges from a shoot, the quicker it will thicken and set into its new position. The thicker a branch is, the longer it will take to set.
Watch for wire suddenly cutting into the bark during the Summer as the wood will thicken dramatically during this period, however, shallow wire-marks are not a great problem and will disappear within a few months to a year (again depending on the strength and vigour of the individual branch).
As with all conifers, branches should always be left with enough foliage to support them, never prune so heavily that a branch is almost devoid of foliage or it will die off.
Junipers begin to come to life from early April as temperatures begin to rise at the beginning of the growing season by producing a full flush of new buds and leaves. This is followed by new extending shoots through the Summer until early Autumn.
The foliage mass can be repeatedly pruned to shape throughout the growing season. However, after repeated pruning the foliage mass becomes very dense and can block air and light from getting to the lower and interior branches causing them to weaken and potentially dieback. It is therefore important to thin out the foliage mass periodically to ensure even distribution of air and light to the foliage as a whole.
Pinching and Scissor Pruning Juniper Foliage
Junipers should be pruned using a mixture of two techniques, scissor pruning and pinching out. Foliage or shoot growth that has hardened, or is too strong to be pinched out using the technique described below must simply be cut with scissors. Pinching such growth will require a lot of effort and very often the green bark will come away leaving a very thin piece of lignified wood behind.
Pruning Mature (Scale) and Immature (Needle) Foliage
The tips of immature needle foliage on a Juniper will all tend to extend new growth and will all need to be pruned on a regular basis. However, only a relatively small number of shoots on a mature scale foliage Juniper will extend. It is these shoots that should be pinched, or scissor-cut. Mature, scale, foliage that is not extending does not require pruning and doing so will lead to the dieback of the foliage on that shoot.