Dawn redwood bonsai

Placement

Dawn redwood is grown outdoors year-round. It loves sun: give it full light from spring through fall. During the hottest weeks of summer, however, give it partial shade.

Like all temperate trees, it needs the cold of fall to go dormant. Wait for the first frosts before moving it into winter protection. In the ground it is one of the hardiest trees there is, but in a shallow pot its roots no longer benefit from deep soil and must be protected from frost. Where temperatures often fall below 14 °F, overwinter it in a cold frame or unheated greenhouse, which limit temperature swings and drying winds. In milder climates, where nights hover around 25 °F, simply set the pot on the ground out of the wind, perhaps wrapped in insulation. Another option is to bury the pot in the garden up to just over the roots.

Avoid long warm spells that would wake it too early: vent the cold frame on sunny days. Once the buds open, young shoots are vulnerable to late frosts, so shelter it on cold nights in early spring.

Soil mix

The soil has to balance two needs: holding enough water for a very thirsty tree and draining well enough to prevent root rot. A mix of 50% akadama, 25% pumice and 25% lava rock, close to the standard deciduous mix, meets those needs well; add more akadama if you cannot water often, or more lava rock in a very humid climate. Sift the akadama to remove dust, which would clog the mix. Akadama breaks down in about two years, which matches this species’ repotting cycle.

Watering

In summer, dawn redwood drinks a great deal and its soil must stay moist at all times; a tree in full sun can need water every day. Even so, don’t let it sit in water: excess water starves the roots of oxygen and causes rot that is hard to reverse. Never water out of habit: push a finger about 0 in into the soil and water as soon as it feels slightly dry. Soak the whole root ball until water runs from the drainage holes, then repeat a few minutes later. Rainwater is ideal; tap water is still acceptable. Its needs drop sharply in fall, and in winter the bare tree needs water only when the soil dries out.

Fertilizer: use a high-nitrogen fertilizer in spring only, for example a 10-6-6 formula. In summer, feed cautiously with a balanced fertilizer so growth doesn’t become impossible to control, then switch to a low-nitrogen fertilizer, such as 3-6-6, until mid-fall.

Pruning

Dawn redwood buds prolifically, especially around pruning scars. Remove any buds you don’t need right away. In spring, before the buds open, cut back twigs with overly long internodes. As with most trees, vigor concentrates at the top and outer edge of the canopy: prune those areas harder to strengthen the lower and inner branches.

Structural pruning is done in early spring; maintenance pruning, of shoots that grow beyond the silhouette, is repeated two to four times a year, from early spring to late fall. Cut thick branches with a concave cutter and seal large wounds with cut paste. Its strong vigor is hard to control on a small tree, so save it for fairly large bonsai.

Wiring

The branches can be wired, but they are rather brittle. To lower a branch, guy wires are often the better solution: a thin wire anchored to a strong root, another branch or the pot, with rubber padding where it touches the bark. If you do wire, do it in late winter while the branches are bare: choose wire about a third as thick as the branch, wrapped at 45°, and bend by pressing on the inside of the curve, without bending back and forth. Wrap thick branches in damp raffia first. Don’t wire a weak tree or one that has just been repotted.

Growth is fast, so check the wire often: it can scar the bark within one to four months. Remove it by cutting it at every turn, never by unwinding it.

Repotting

Repot every two years in early spring, as the buds swell. The very vigorous roots soon fill the pot and end up pushing the root ball upward, so substantial root pruning is unavoidable. Tease out the old soil with a chopstick, cover the drainage holes with mesh, secure the tree with anchoring wires, fill with fresh soil and water thoroughly. Afterward, shield the tree from strong sun, wind and cold, and wait until it recovers before feeding; new shoots appear within a few weeks.

Its natural habit is the formal upright style (chokkan), with an evenly tapering trunk. It also makes an excellent forest planting (yose-ue), several trees set in a wide, shallow tray with the strongest in the center, and it works for root-over-rock as well. It propagates easily from seed, cuttings or air layering. Pests and diseases rarely attack it; in a pot, the main thing is not to drown its roots.