The juniper is a genus of about 50 - 70 species within the cypress family. They are evergreen coniferous trees or shrubs, which are very popular for Bonsai purposes.
Juniper Bonsai trees sold in stores are often Japanese Garden Junipers, also called Green Mound Junipers (Juniperus procumbens nana). Other popular species are the Chinese juniper (Juniperus chinensis), the Japanese Shimpaku (Juniperus sargentii), the Japanese needle juniper (Juniperus rigida), two central European species: the savin (Juniperus sabina) and the common juniper (Juniperus communis), and three American species: the California Juniper (Juniperus californica), the Rocky mountain Juniper (Juniperus scopulorum) and the Sierra Juniper (Juniperus occidentalis). All these species have similar care guidelines.
The foliage colors range from dark blue-greens to light greens and the foliage can either be scale-like or needle-like. Scale junipers usually have needle-like foliage when they are young (called juvenile foliage), the typical scale-like foliage appears later. After heavy pruning or bending, overwatering or other stress often juvenile foliage will grow again. It can last a few years until enough normal scale-like foliage has grown and all the needle-like foliage can be removed.
The berry-like cones are round or oval, depending on the species they measure around 2 cm (1 inch), sometimes down to 3mm, and they need a year or two to ripen. The seeds are round or edged. The cones are often eaten by birds who spread the germinable seeds later with their droppings.
Junipers are very suitable for creating deadwood (jin and shari). This is due to the fact that live veins below a broken or for other reasons dying branch will dry out and die. This results in natural deadwood which is peeled, polished and bleached by climatic conditions and is very durable in case of the juniper. The triad of green foliage, reddish-brown or yellowish-brown bark and silvery white deadwood is very appealing.
There are two groups of Junipers, one with scale-like foliage and the other one with needle-like foliage.
The two most popular juniper species for bonsai of the group with scale-like foliage are the Chinese Juniper and the Japanese Shimpaku (which is a variety of the Chinese Juniper which was originally found in the Japanese mountains). Both have scale-like foliage with a color ranging from yellowish-green to bluish-green or grayish-green. The Itoigawa Shimpaku is very popular due to its delicate emerald-green foliage. There are numerous varieties and cultivars of the Chinese Juniper many of which are not easy to distinguish with certainty, care guidelines for these varieties are highly similar. The Savin is a juniper from southern Europe, North-Africa and some parts of Asia with scale-like foliage which can be finer or coarser and of different shades of green depending on its origin. All parts of the Savin are poisonous. The California Juniper is native to California and has bluish-grey scale-like foliage. In nature it grows as a small tree or shrub. The Rocky Mountain Juniper grows in western North-America and can become a tall tree. Its leaves are scale-like, quite coarse and can be dark green or bluish-green. The Sierra Juniper is a shrub or tree native to the western United States, growing in mountains at altitudes of 800–3,000 meters (2500 to 10000 ft). Its leaves are scale-like and grayish or dark green and tend to grow quite dense.
There are also popular juniper species with needle-like foliage. The Japanese Needle Juniper has sharp, dark green, stinging needles with a narrow white line along their length. The Green Mound Juniper Bonsai is also from Japan and also bears needle-like foliage, but the needles are shorter, more compact, bluish-green - almost like scale-like foliage. This plant grows as a ground covering shrub if it is not shaped. The Common Juniper in native to Europe, North-America, Asia and North-Africa. Its needles are sharp but smaller and more delicate than those of the Japanese Needle Juniper. In nature it grows in a columnar shape or as a depressed shrub.
Specific Bonsai care guidelines for the Juniper Bonsai
Place the tree outside, year-round, on a bright spot with lots of sunlight. The Juniper cannot live indoors. During the winter some species change their foliage color during frosty periods to a purplish or yellow brown which is connected with their frost protection mechanism. In spring they will turn green again.
Be careful not to water too much, as the juniper roots don't like soil wetness. Before you water, the soil should dry slightly. Misting the tree can be done regularly, especially after the tree has been repotted because it benefits from air humidity.
Use normal organic fertilizer pellets or balls every month during the growth season or a liquid fertilizer each week. If strong growth is desired some higher nitrogen levels can be applied in spring.
To develop the foliage pads, long shoots which stick out of the silhouette can be pinched or cut at the base with sharp scissors throughout the growth season. Do not trim the juniper like a hedge because the removal of all growing tips will weaken the tree and the cut will turn the needles brown. When the foliage pads become too dense they must be thinned out with sharp scissors at the base. The Juniper Bonsai is generally a strong tree that also withstands aggressive pruning quite well. But it cannot bud again from bare tree parts, so take care that there is some foliage left on every branch you want to keep alive.
Junipers which are produced for Bonsai purposes are already wired quite heavily in most cases when they are still very young. Dramatically twisted shapes are very popular and correspond with the natural shapes that used to grow in the Japanese mountains in former times. Junipers can be strongly bent, if necessary wrapped with raffia or tape as a protection, but you must be careful with parts which possess deadwood. Those parts break easily. If they are large and old, you can split the deadwood off in order to bend the more flexible living parts. The foliage pads should be wired and fanned out after thinning when necessary, to let light and air get in. Otherwise the inner parts of the foliage pads will die. In addition to this, the danger of pest infestation is increased if the pads are too dense. From the aesthetic point of view we also want to achieve unobstructed structures and want to prevent the juniper from looking like broccoli.
Repot the Juniper once every two years, very old trees at longer intervals, using a basic (or somewhat more draining) soil mixture. Don't prune the roots too aggressively.
Use seeds or cuttings.
Pests / diseases:
If junipers are well cared for and placed in an ideal position they are quite resistant against pests. It is important though not to let the foliage pads get too dense, because otherwise pests can settle in them more easily. During winter the junipers must be kept in a place with enough light and they must be checked for pests regularly because pests can even occur in winter. Junipers can sometimes get infested with spider mites, juniper scale, juniper aphids and juniper needle miners as well as juniper webworms for example. Spray with Pyrethrum.