Coast redwood bonsai

Placement

In the wild, Sequoia sempervirens lives in a foggy coastal strip with mild winters and cool summers. As a bonsai, it needs full sun from spring through fall: bright light keeps growth compact. In shade, internodes stretch, needles get larger and the tree weakens. During the hottest weeks, however, protect it from heat: above 84 °F, a shade cloth that filters about a fifth of the light is enough; the hotter and drier the air, the heavier the shade should be. Sheltered this way, it can even handle spikes above 100 °F.

Winter is its weak point. Although it is hardy in the ground in mild climates, a redwood in a pot cannot take frost: its roots suffer as soon as the temperature drops below 32 °F, and a cold snap can kill branches or even a large part of the tree. In a cold climate, overwinter it in an unheated greenhouse or a cool, bright room, then move it back outside once the frosts are over.

Soil mix

Coast redwood has high water and nutrient needs. Choose a mix that holds moisture well yet drains freely; a high proportion of akadama meets both needs. The tree also prefers acidic soil. Pot shape is up to you: narrow and deep or wide and shallow, depending on the style you want. Keep the soil mass down by choosing a smaller pot and leaving more foliage on the tree.

Watering

Never let the root ball dry out: that is the golden rule. Check the surface of the soil every day and water as soon as it feels dry. Depending on heat, wind and pot size, that can mean watering daily or every other day in summer, and much less in winter. Moist does not mean wet: soil that stays waterlogged rots the roots. In a dry climate, mist the foliage each time you water.

Fertilizer: an organic fertilizer is preferred. A tree in development gets moderate feeding from spring through fall; high-nitrogen fertilizer is given only in spring, because in summer it would trigger growth you cannot control. For a refined tree, feed more lightly: you will get shorter needles and tighter internodes.

Pruning

Coast redwood grows upward and produces a huge number of buds, especially around pruning wounds. Rub off unwanted ones as soon as they appear, with a fingertip or tweezers. At each fork, keep only two shoots: when several shoots arise from the same point they form a whorl, and the callus that builds up thickens the wood there until the trunk or branch becomes wider at the top than at the bottom. Also pinch young shoots so they do not grow too long.

Cut only wood that has turned woody: pruning a shoot that is still green and soft sends new growth back to the base of the branch. Three windows work well: spring before the buds break, to shorten twigs with overly long internodes; summer, once the first flush has hardened; and late fall to early winter, once next year’s buds have formed.

Styles: formal upright, conical as in nature, is the most common; informal upright also suits it. Its vigor is easier to manage on fairly large bonsai.

Wiring

Redwood branches will bend, but they are brittle. To lower a bottom branch, a guy wire, run from the branch to a solid anchor point, is often a better option than wrapping it. Wire only woody growth, never soft, fleshy green shoots. Wire in the same windows as pruning: spring, early summer, or late fall to early winter. Wiring done from early to mid fall can be disastrous.

Use wire about one third the thickness of the branch, wrapped at roughly 45°, and protect thick branches with damp raffia before bending them. Bend gradually, pushing from the inside of the curve, and avoid bending the same spot twice. Redwood thickens quickly: check the wire often and remove it as soon as it starts to mark the bark, cutting it at every turn rather than unwinding it.

Repotting

Its vigorous roots fill the pot quickly and push the root ball upward, so repot about every two years. Do it in mid to late spring, when the buds swell and the tree becomes active again. Prune the roots firmly, but never bare-root the tree completely: as with other conifers, always leave some roots in their old soil. After repotting, shelter the tree from strong sun and wind, and mist the foliage regularly while it recovers.

Propagation: seed, branch cuttings, even from thick branches, root cuttings and air layering all work well.

Pests and diseases: coast redwood is rarely attacked. In a dry climate, watch for spider mites. In a pot, a fungal disease that leaves red spots on the foliage can appear; a simple fungicide clears it up. The main danger remains overwatering, which rots the roots.