Junipers are, along with pine, another of the common species sought by beginning bonsai enthusiasts. And for good reason: it’s a beautiful species that tolerates a wide variety of conditions well.
Junipers make an especially good species for the kengai (cascade) style in which the trunk and branches grow out over the pot and below the horizontal surface.
Junipers enjoy full sun and tolerate moderately dry soil conditions. Soil shouldn’t be allowed to dry out completely, however. Copious amounts of water are fine, provided there is adequate drainage.
Feeding should be carried out every three to four weeks from early spring to autumn. Opinions vary, with some preferring organic fertilizers but this seems to be as much an ideology as a view based on good botanical science.
Man-made chemical fertilizers can be harsh, though, and should be used with care to ensure the proper proportions. Half-strength of 20-20-20 NPK (Nitrogen – N, Phosphorus – P, Potassium – K) is common. Avoid applying during the hot months or within a few weeks after repotting.
Repotting is a good time to trim roots, but gradual reduction is best. Cut off no more than 1/3. Trees younger than 10 years old should be repotted every two years, older ones every three to four.
Soil mixture is commonly 60% soil, 10% peat and 30% coarse sand, but there are many variations on the relative amounts and material. Loam, leaf mold and sand in equal proportions is a viable alternative.
Repotting is also a good time to carry out pruning of unwanted branches. Wiring is best done in late autumn, however, after the major growing season has tapered off. If carried out during active growing season results will come quicker, but careful observation is needed to avoid scarring.
Many bonsai artists use pinching to remove the new shoots that occur during the active growing season. Just take the new growth between thumb and forefinger and give a sharp twist to remove. Take care not to move or bend the tree or branch. The procedure should be carried out frequently during the growing season to control the growth of new foliage.
Red spider mites are a common pest of this species. Look for yellowing foliage. Check under the branch for small spots. To double-check, hold a white sheet of paper or a tissue underneath. Sharply tap a branch without too much force. This should dislodge a few if they’re present. If they move, you know you have something you don’t want on your tree.
A home recipe of nicotine solution can be prepared by soaking tobacco in water overnight, but a commercial insecticidal solution will be more effective.
After the insecticide has operated for a day, spray the foliage with water daily during the growing season and allow to dry in full, but early sun. Full sun should be avoided for a few weeks right after repotting.