Japanese cedar bonsai

Placement

Japanese cedar is grown outdoors. It likes sun, but only where temperatures do not climb too high: during hot summer weeks, give it partial shade or a bright, well-ventilated spot out of direct sun. It enjoys high humidity and does poorly in dry heat.

In winter it tolerates little frost, especially in a shallow pot where the roots are very exposed. A cold greenhouse kept frost-free is ideal. The foliage often changes color in winter, taking on olive, brown or purple tones that are stronger the more sun the tree gets and the colder it becomes. This bronzing is nothing to worry about: the green color returns in spring.

The Japanese cedar plant profile describes the tree in the ground, its hardiness and its cultivars.

Pests and diseases: Japanese cedar resists pests and diseases well. Spider mites and scale insects are the most common; misting the foliage regularly helps prevent them. Powdery mildew and other fungal foliage diseases can also appear, and good air circulation keeps them in check. If a problem takes hold, use a treatment suited to it.

Soil mix

Use a free-draining standard bonsai mix with a pH between 5.5 and 7. Since the tree drinks a lot, make sure above all that excess water runs freely out of the drainage holes.

Watering

During the growing season, Japanese cedar needs plenty of water and the root ball must never dry out. Water without a fixed schedule: check the soil often and water as soon as the surface starts to dry, until water runs out of the bottom. To raise humidity, also water over the foliage and wet the bench and the ground beneath the tree. The water should have a pH between 5.5 and 7: if your tap water is very hard, use rainwater instead. In winter, while the tree is dormant, water only when the soil starts to dry.

Feeding: from the start of growth until fall, apply a solid organic fertilizer once a month, or a liquid fertilizer every one to two weeks. Adjust the formula to the season: high in nitrogen as buds break, balanced from early summer, then low in nitrogen from late summer to strengthen the roots before winter.

Pruning

Japanese cedar buds readily all over the canopy, which makes it possible to build compact foliage pads.

• Pinching: throughout the growing season, pinch new shoots as soon as they reach 0–1 in. Constant, regular pinching spreads vigor through the whole tree, keeps the outline and encourages new buds. Pinch with your fingers: needles cut with scissors turn brown at the cut, as on junipers.
• Thinning: remove shoots growing from the undersides and bases of branches, along with excess old foliage, so light and air reach the inside of the tree.
• Structural pruning: do heavy pruning early in spring. Make clean cuts, because the bark and cambium easily come away from the wood. Wounds turn brown, but new growth soon hides them.

Dwarf cultivars such as ‘Elegans Nana’ and ‘Globosa Nana’ need less pinching, but they grow slowly and take much longer to thicken their trunks. ‘Elegans’, ‘Elegans Compacta’ and ‘Pyramidata’ are commonly used.

Styles: the classic style is the formal upright, with a single or multiple trunks, echoing the tree’s natural shape. Japanese cedar is also grown with twin trunks, as forest plantings and on rock, from extra-small to medium sizes; the Japanese variety even suits shohin. Branches are presented horizontally or slightly drooping, with the foliage trained upward so the branch structure shows.

Wiring

Wire from mid-spring to midsummer so branches have time to heal before winter. Young branches are easy to wire; just take care not to crush the foliage. Choose aluminum wire, which is softer than copper and easier to remove without damaging twigs. Use wire about one-third the thickness of the branch, coiled at about 45°.

Branches are supple but split easily where they join the trunk or a larger branch. Older branches become stiff and brittle, so position them gradually. Bend a branch more than 1 in thick slowly, over several weeks, because sudden movement splits the bark; wrap it in raffia before wiring. Guy wires are a good way to set branch angles. Check the wire regularly and remove it by cutting it at each turn before it marks the bark.

Repotting

Repot a young tree every two to three years in mid-spring, as new buds start to grow. Older trees are repotted less often, depending on root development. The roots grow at a moderate pace, so avoid heavy root pruning.

Propagation:

• Seed: sow outdoors in spring.
• Cuttings: they root very easily from summer to early fall, using ripened wood late in the season.
• Air layering: also possible.