Shimpaku Juniper Bonsai Care Guide
Juniperus chinensis 'Shimpaku', also known as Juniperus chinensis 'Sargentii', is native only to the Japanese islands of Hokkaido and Yakeshima. The name "Sargentii" is a nod to Charles Sargent, the American botanist who identified this juniper on Hokkaido in the early 1890s. The low-growing evergreen may reach a height of one to three feet and a spread of one to five feet across in its natural habitat.
This juniper has a rich and interesting history, especially considering it has been around in the bonsai world for little more than a century. In the early 1900s Shimpaku began enjoying wild popularity as a bonsai in Japan. As word of this attractive species spread it became rarer and rarer, which resulted in the price skyrocketing to as high as today's equivalent of $10,000. This only fed the craze to find and collect Shimpaku from the wild, which unfortunately is often on mountainsides, making the process of obtaining the tree difficult and dangerous. Still, collectors and sellers persisted, until today the species is facing potential extinction in the wild.
The foliage on Shimpaku is deep mint green, needle-like when the tree is young, and scale-like as it matures. The light brown bark peels and develops more texture with age. The underlying tough, resinous wood is one of the most beloved traits of this species, as it is extremely amenable to textural elements such as jin and shari. Like all junipers, Juniperus chinensis Shimpaku bears small berry-like structures which aren't true berries – they are actually the female seed cones. The seed cones on Shimpaku have a bluish color.
This tree is extremely hardy and can tolerate a wide range of climate conditions. It should not be kept as an indoor tree. During the winter the Shimpaku should be allowed to go dormant, while protecting its roots with a form of cool shelter like an unheated garage or shed. In the hottest days of summer the bonsai appreciates a good misting of its foliage several times daily, but otherwise does just fine in the heat, even to temperatures of 90 degrees F.
Shimpaku should be kept moist but not too wet as it is prone to root rot. Do not allow the surface of the soil to become dry to the touch. In winter watering may be reduced but the plant's soil should still be checked fairly frequently to make sure it's not dried out.
Feed a high nitrogen fertilizer diluted to half-strength, every two weeks from early spring to the middle of summer. Refrain from fertilizing in the hottest days of summer. From late summer throughout winter give a low nitrogen fertilizer. Feeding can be alternated with a fertilizer made form acid-loving bonsai. Refrain from feeding a weak or sick tree, or one that has been repotted in the previous two to four weeks.
Styles – the Shimpaku Juniper bonsai will take to nearly any form, including informal and formal upright, slanting, and literati. The trunk can be trained to twist in a stunning display, even more striking with the incorporation of deadwood into the whorling mass.
There is some matter of controversy regarding pinching of junipers. Some enthusiasts insist that pinching will weaken foliage. Others advocate pinching over cutting. Pinching is usually best when only minor pruning is needed. With most all other pruning needs, cutting is the way to go. After cutting is done, the tips of anything cut will turn black/brown for a period of time. This is normal and should not alarm you. Regardless of the method you choose, new shoots should be allowed to grow to a couple of inches beyond the foliage pad, then trimmed. Do not trim the ends of the remaining shoots. Continue this pattern of trimming until the middle of September. Undesirable branches should be pruned.
Shimpaku may be wired, which is best carried out in autumn or early winter so that the branches adjust during dormancy. Keep an eye on the wire during the growing season to be sure it doesn't cut into the bark. Wire may remain for up to a year. Never wire a bonsai just after it has been repotted.
Shimpaku may be propagated by taking heel cuttings in autumn. These are taken from side shoots, pulling them in the opposite direction from the tip of the stem. Heel cuttings can also be cut from the main stem using a knife. Put the cuttings in an acidic rooting medium and keep them warm and well-lit.
Junipers should be repotted every one to two years, in mid-spring. For trees older than 10 years, repot every three to five years. The pot should not be shallow. Be judicious in root pruning, removing a maximum of a third of the roots. The transplanted tree should be placed in the shade out of the wind for three to six weeks. Water and mist daily. Fertilizing can commence after six weeks as long as the foliage is green and soft.
Shimpaku Junipers, like all conifers, have a symbiotic relationship with Mycorrhizal fungus. They should never be bare-root for this reason.
Insects/Pests & Diseases:
Spider mites and fungus are potential problems for this bonsai. Check it frequently and if signs of mites are observed, such as yellowing foliage, rinse the plant with a mixture of a teaspoon of dish liquid to a quart of water. If gray or black spots are seen, the tree may be treated with a mild fungicide.