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Botanical Name – Juniperus chinensis
Botanical Name – Juniperus chinensis
Common Name – Chinese Juniper
Native to – Himalayas, China and Japan
Botanical Information – A variable growth habit as a species; it can be a tree up to 60 feet or more shrub like. Young juvenile leaves are opposite or whorled, linear, pointed and spreading with a white band above. Older mature foliage is scale or thread-like and usually a lustrous green. Sexes are on separate plants (dioecious) and most cultivars have been selected from male (staminate) plants.
General – Juniperus chinensis and its many cultivars have been the subject of much discussion by horticulturists and botanical professionals for many years. Some of the cultivars, Shimpaku in particular, have been assigned from one species to another and back again, making their actual assignment to a species confusing to all but the horticulturally insane individuals that inhabit the halls of arboreta and other scientific establishments. I have included the Shimpaku forms under Juniperus chinensis, as have many others, but some still list it under Juniperus xMedia “Shimpaku” which identifies it as a hybrid plant. You may also see Shimpaku listed as Juniperus chinensis “Sargentii”. No matter how it is listed, it is a wonderful plant for bonsai.
From a bonsai perspective the Shimpaku forms have been a mainstay of the art form in Japan because of their soft deep green foliage and rugged, strong looking trunks. Some of the other cultivars that are beginning to be used are wonderful bonsai subjects in their own right. Of particular note is the famous John Naka forest “Goshen” in the U.S. National Arboretum that is made from the cultivar “Fomenia”. Most but not all forms of Chinese juniper have both juvenile foliage which is stiff and usually prickly and the softer mature foliage that appears more scale or thread-like. For the cultivars, I have only listed the more commonly available in the bonsai trade, but there are many others that should be tried.
Cultivars – Shimpaku – Deep green scale like foliage
Kishu Shimpaku – Smaller and tighter foliage than Shimpaku
Blaauw – Blue-green foliage with more upright growth
Fomenia – Blue-green with prickly juvenile foliage
San Jose – Light green foliage, rugged trunks that thicken fast
Heitz Columnaris – Medium green foliage, very upright; good for Formal upright style and tall forest plantings (pictured above)
As with most conifers, Junipers prefer full sun all day long. They are hardy and can handle high temperatures in their root zone, which makes them perfect for bonsai use as long as an adequate supply of water is available.
The Chinese Juniper is hardy and rated at a U. S. zone 4 making it tolerant of the cold. Even though it is hardy in nature when grown as a bonsai in a container protection of the roots during the winter is still required in Zones 5 and lower. It can be as simple as placing the container on the ground and covering it with pine needles. Placement should be such that the roots don’t alternate between freezing and thawing and freezing again. It is far better to keep the roots frozen. I have grown the cultivar “Heitz columnaris” outside year-round in Zone 6.
This juniper does like to have an adequate water supply, but appreciates being a little on the dry side between waterings. Never let the plant completely dry out but if the soil is dry to the touch at the surface a watering would be in order. Over-watering a Juniper is the worst thing that can be done. Too much moisture will encourage the roots to rot and once rotting starts it’s difficult to recover from without immediate attention and great care.
Junipers are not heavy feeders and if given too much food they will grow loose and spindly. Fertilizer should only be applied to keep the plant in good color. Monthly applications of a good general purpose dry or liquid fertilizer at the recommended dosage during the growing season is more than adequate for most Junipers. Never fertilize a plant that has been repotted for at least 30 to 60 days. I have found that a spring application of dry blood and bone meal along with summer applications of commercial liquid preparations keep the foliage looking quite nice all year long.
The initial pruning of a plant to form its intended shape will usually be drastic. Once the basic shape has been achieved pruning will be pretty much limited to hand plucking the new growth to encourage pad development. The Chinese Juniper should never be sheared with clippers as their foliage will brown and not be visually appealing. However, in the early stages of a tree’s development, shearing can be used as a pruning technique but this should only be used on trees not for public display. For the more established or finished plants plucking by hand is the best method to keep the foliage in shape. When plucking new growth by hand care should be taken as the new growth is delicate and easily pulled off at the base. Heavy pruning should be done in the late winter while pruning or plucking for pad development can be done anytime during the growing season.
Wiring is best done in the fall and winter. The side branches are slow to develop girth and not subject to girdling quickly. Wire on trunks should be inspected at least twice annually, once in the late spring and again in the fall. Wire can be maintained on a plant for 1-2 years without any detrimental affect but should be inspected on a regular basis. Look for signs of branch swelling (girdling) around the wire as your signal to remove the wire.
Repotting should be considered every 3-5 years for the average aged bonsai. Established or older bonsai can go 5-10 years between repottings in that their roots are slow to develop. However, an annual inspection of the roots should be done in the very early spring prior to the onset of growth to verify their health. Root reduction on new trees should be done in multiple stages and never attempted on the whole tree in a single repotting session. The typical rule of thumb has been to only do 1/3 in any given repotting session. Soil for most Junipers should be course in structure and contain at least 25% air and only a moderate amount of humus. Junipers always enjoy a generous clay component to their soil makeup.
Propagation is by cuttings taken in the fall or late winter. Seed can also be used but are notoriously slow and random at sprouting, sometimes taking up to 3 years. Grafting is also done for any number of purposes but mostly for design reasons. Grafting should be done during mid to late winter. The most typical graft is the side-veneer or the cleft graft. Approach grafting may be attempted and is a good way to get a new branch in the right place or even to change the type of foliage on the whole tree. It is not uncommon to see San Jose Junipers approached grafted with Shimpaku on the branches to make a bonsai with both the lovely trunk structure of the San Jose and the outstanding foliage of the Shimpaku.
Pests and Diseases
Chinese Juniper is mostly affected by mites and occasionally bag worms (in the Eastern parts of the United States). A regular spraying program to keep mites under control is essential. Plants that have a bad infestation of mites will often have a white cast to them instead of that deep green. If you suspect a mite infestation, take a piece of white paper and shake a branch over it. If mites are present you will see them crawling on the paper. You may need a magnifying glass as mites are extremely small. Mites usually appear later in the spring when the weather warms up and the relative humidity is moderate to low. Frequent spraying of the foliage with water will help keep the Mites under control. This particular Juniper seems to be relatively resistant to the typical fungal diseases like Apple Cedar Rust and its related fungi. While it is not often affected by these fungi it should be included in a summer spraying program, particularly in those areas with wet spring weather and humid summers.
|October 2007||November 2007|
|November 2008||November 2009|