Japanese Dwarf Garden Juniper - Juniperus procumbens nana
General Information: This is the tree that is most often used for the ubiquitous "mall bonsai". In spite of this bad press, it does in fact make a fine bonsai if it is properly trained and cared for (unlike the average "mall bonsai").
This juniper has a low, spreading habit that makes it ideal for cascade and semi-cascade styles. Specimens grown in a nursery or specifically for bonsai can be used for many styles, but probably not for formal upright. In nature it grows as a small ground-cover shrub. The foliage is bright green.
Lighting: Full sun.
Temperature: Tolerates a wide range of temperatures, including freezing, however, roots must be protcted from excessive heat or cold.
Watering: Spray the foliage with water daily during the growing season. Water when the soil is moderately dry (to a depth of 1/2 to 1 inch) but do not let the soil dry out completely.
Feeding: Simon and Schuster's recommends feeding junipers from early spring to autumn ever 20-30 days using a slow-acting organic fertilizer. If you prefer to use chemical fertilizers, apply a half-strength solution every other week of a reasonably balanced fertilizer, such as Peter's 20-20-20. You may wish to alternate with an acidic fertilizer such as Miracid. 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.
Pruning and wiring: 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.
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, and must be removed immediately if this happens. If necessary, the tree can be re-wired after removing the old wire.
Propagation: Cuttings rooted under mist, layering.
Repotting Reduce the roots gradually, removing no more than one third of the roots at each repotting. Repot young trees (up to 10 years) every other year. Repot older trees every 3-4 years. Repotting is best done in spring. 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.
Simon and Schuster's recommends 60% soil, 10% peat, and 30% coarse sand. Rémy Samson recommends 1 part loam, 1 part leaf mold, and 1 part coarse sand. Peter Chan recommends 1 part loam, 1 part peat, and 3 parts coarse sand.
The tree should be protected from wind and direct sun for a month or two after repotting.
Pests and diseases: Junipers are a favorite victim of red spider mites. If the tree appears weak, with yellowing foliage, it may have spider mites. To check for spider mites, hold a sheet of white paper under a branch and gently shake the foliage. If the paper comes away with many small dots that move, it has spider mites. To combat spider mites, spray with insecticidal soap or a nicotine solution (which can be made by soaking tobacco in water overnight).