Coast redwood

Identification and origin

Sequoia sempervirens belongs to the Cupressaceae family. It is native to a narrow coastal strip running from southwest Oregon to central California, and it has become naturalized in France, Great Britain, Italy and the Balearic Islands. In the wild it rarely grows more than about sixty kilometers from the ocean: it depends on summer fog, which cuts evaporation and offsets the drought of a climate with cool, rainy winters and dry summers. It grows mainly on alluvial terraces and coastal plains, from sea level to about three hundred meters, rarely higher. It is the state tree of California.

Its records are spectacular: old trees commonly reach sixty to a hundred meters, and the tallest ever measured tops a hundred and fifteen meters. The trunk, often three to more than four meters across, flares into buttresses at the base and frequently carries burls, rounded swellings packed with buds. The oldest known tree was about two thousand five hundred years old. In cultivation, expect 59–200 ft in height and 15–24.5 ft in spread, with fast growth, around 3 ft a year in a young tree.

The red-brown bark, fibrous and deeply furrowed, can be 12 in thick and shields large trees from fire. The foliage comes in two forms. On leading shoots and fertile twigs, the leaves are short, triangular and pressed against the stem. On side branchlets they are linear, flat and stiff, arranged in two rows, bright green above with two white bands underneath; they measure 0 in to 1 in. The female cones, egg-shaped and red-brown, measure 0–1 in and ripen in their first year.

Do not confuse it with giant sequoia from the Sierra Nevada, which is bulkier but shorter, or with dawn redwood, its Chinese cousin that drops its needles in winter. A few cultivars exist: ‘Adpressa’, a dwarf with white tips; ‘Albospica’, with white new growth; ‘Kelly’s Prostrate’, a low, spreading form; and ‘Yurok Prince’, a shrub of 2–4 ft.

Light

Coast redwood grows in full sun or partial shade, with as little as two to six hours of direct sun a day. It is one of the most shade-tolerant conifers: when young, it establishes easily under the canopy of other trees. In a container, full light gives more compact growth, but shield the tree from scorching sun during hot summers.

Watering

It likes soil that stays moist; it tolerates occasionally wet ground but not drought. Outside its foggy home climate, a young tree needs deep watering during dry summers: check the soil well below the surface and water as soon as it starts to dry, rather than on a fixed schedule.

In a pot, never let the root ball dry out. Check the surface every day during the growing season: daily watering or watering every other day is often needed, and much less in winter. Even so, soil that stays soggy all the time rots the roots. In dry air, mist the foliage when you water.

Potting mix

It prefers deep, well-drained, acidic soil rich in organic matter, ideally with a pH below 6. It does not tolerate dry, compacted ground. In a container, choose a mix that holds water but still drains freely.

Temperature

Coast redwood is hardy in USDA zones 7a to 9b. Planted in the ground, its cold tolerance limit lies between 10 °F and 19 °F, depending on the tree and how long the freeze lasts. A tree in a pot is far more fragile: its roots are damaged as soon as the temperature drops below 32 °F, and frost can kill whole branches. Shelter it in winter in a cold, bright room or an unheated greenhouse. It handles strong heat, above 100 °F, when shaded, but it is sensitive to salt spray.

Repotting

In the ground, give it room to match its size: a mature tree needs more than 59 ft of open space. Its roots run deep and spread widely, with no taproot.

In a pot, its vigorous roots fill the container quickly and push the root ball upward. Repot about every two years, in mid to late spring as the buds swell, pruning the roots firmly. Never bare-root it completely: always keep some of the old soil around the roots. After repotting, protect the tree from strong sun and wind.

Pruning

In the ground it needs very little pruning: with age it sheds its lower branches on its own and, in dense stands, it self-prunes. Simply remove dead or broken wood.

In a container it produces a great many buds, especially around pruning wounds. Rub off unwanted ones as soon as they appear. Prune only shoots that have already turned woody: cutting a shoot that is still soft sends new growth back to the base of the branch. Work in spring before growth starts, in summer once the new growth has hardened, or in late fall.

Propagation

• Seed: no pretreatment is needed. Sow on moist, mineral soil in partial shade. Germination is low, around ten percent, because many seeds are empty. Seedlings have no root hairs, so their soil must never dry out. They can grow 18 in in their first season.
• Cuttings: cuttings taken from young plants two or three years old root very well; those from old trees root poorly. Root cuttings and large branch cuttings also work.
• Air layering: a reliable method.

In the wild it regenerates mostly from sprouts that arise from the stump, the base of the trunk or the burls, and can grow 7 ft in a single season.

Common problems

A single symptom can have several causes: browning foliage can come from frost, a dry spell, overwatering or a fungus. Look at the tree and its growing conditions before treating.

• Insects: they rarely cause significant damage.
• Branch canker: it can girdle and kill stems and branches.
• Heart rot: mainly in old trees with wounds.
• Root rot: in a pot, in soil that stays waterlogged.
• Spider mites: in a pot, in dry climates.
• Red spots on the foliage: a fungal disease that can appear on container-grown trees and responds to a simple fungicide.
• Compacted soil: foot traffic around the trunk damages the roots.
• Rodents: they can strip the bark from seedlings.

Toxicity

No toxicity has been reported for dogs or cats: coast redwood does not appear among the plants listed as toxic to these animals. Even so, keep children and pets from chewing on any part of it.