The Shimpaku Juniper is native to Japan, the Kurile Island and the Sahalin Peninsula. It prefers rocky, well-drained soils. In its natural range, it is most often found growing near the sea. The foliage is needle-like on young trees and scale-like on older trees. The fruit is a small, hard, bluish berry. One of the best characteristics of Shimpaku is its hard resinous wood; ideal for advanced sculptural techniques such as jin, shari and sabamiki.
The Shimpaku Juniper does best outside. It needs plenty of natural sunshine and temperature changes associated with the seasons. When kept outside, it can tolerate just about any condition. Make sure it gets afternoon shade in the summer.
Bonsai trees live in small pots and their world dries out much quicker than for plants in the ground or in bigger pots. The more sunlight and warmth your bonsai receives, the more often it will need water. Striking a balance between not enough water and too much water can be a bit tricky but is very important. Spray the foliage often during the growing season. Water thoroughly and deeply when it needs water and let it catch its breath before watering again. Place the entire pot in a sink of water an inch or two deep and let the water absorb through the holes in the bottom of the pot. Another favorite way to know if it needs watering is to lift it. You can get a sense for whether it needs watering by its weight.
An inexpensive moisture meter takes the guesswork out of watering. We sell them on our website. We pot our bonsai trees in soil blended specifically to drain well, so it’s almost impossible to over water.
Leaves want humidity to keep them green and healthy. Mist occasionally during the week. A humidity tray is a great way to increase humidity. These shallow trays filled with small stones have water in the bottom of the tray. Make sure the water does not reach the bottom of the bonsai pot. As the water evaporates, it creates a moister environment.
Fertilizing a bonsai is essential to its health because the nutrients in the soil leave very quickly with the water. When new growth appears in the spring, it’s time to start feeding your bonsai. You should not fertilize during the hottest part of the summer (July-Mid August in the Northern Hemisphere), or if the tree is weak or has recently (2-4 weeks) been repotted.
To develop the foliage, pinch out the tender new shoots using your fingers. Do not use scissors, as the cut needles will turn brown. Pinching must be done continuously during the growing season. Prune undesirable branches (especially those growing straight down from their parent branch) when repotting or during the growing season.
Use the thinnest training wire that will hold the branch in the desired position. DO NOT WIRE A BONSAI JUST AFTER REPOTTING. Wind the training wire in the direction the branch is bent in order to keep the wire from loosening. Wrapping the wire too tightly will cause scarring. Begin at the base of the bonsai t tree and slowly rap the wire around the trunk to anchor. Continue along the branch you wish to train. To remove wire, cut the wire carefully from the branch. DO NOT UNWIND WIRES. This could cause the branch to break.
Wiring is best done in autumn or early winter, so that the branches can become accustomed to their new position while the tree is dormant. Wiring done at other times must be watched carefully for signs of wire cutting into the bark. Wire must be removed immediately if this happens. If necessary, the tree can be re-wired after removing the old wire.
Repotting is best done in spring. Young trees (up to 10 years) can be repotted every other year. Repot older trees every 3-4 years.
Shimpaku Junipers can also be repotted in autumn if necessary since they enter a period of renewed root growth at that time. Extensive root pruning in autumn is probably not a good idea, however. The tree should be protected from wind and direct sun for a month or two after repotting.
Insects and Diseases:
Spider mites love Junipers. It’s hard to know that they have arrived because they are tiny little things, so spray for them whether you see them or not. You can spot spider mite trouble by the discoloration of foliage, usually gray and usually at the tips. But to know for sure, place a clean sheet of white paper under the branches of your bonsai and gently tap the foliage. Tiny specks will fall onto the paper. Watch the specks carefully for a moment and see if any of them get up and try to leave. A moving speck is a spider mite. Use a mild insecticide that lists spider mites. Spray with insecticidal soap or a nicotine solution (which can be made by soaking tobacco in water overnight.)
Junipers are also susceptible to fungus problems, especially in shadier, darker and cooler spots. Like spider mites, discoloration of the foliage is what you will see but this time it will be black or a pale lavender, grayish color. You can prevent fungal problems by keeping your bonsai in a well-ventilated area. Air circulation also encourages cell growth. Fungus problems are more likely during the dreary, wet fall and winter days and into the soggy spring days too. Use a mild fungicide and keep the air flowing to chase away fungal problems.