UK context

The coast redwood, Sequoia sempervirens, evolved in a narrow fog belt from southern Oregon down to the Santa Cruz mountains. What keeps it there is not sunshine but moisture — persistent coastal fog, high annual rainfall, and mild winters that rarely freeze.

Britain's Atlantic seaboard provides a reasonable approximation of those conditions. The west of Scotland, Wales, Cornwall, and almost all of Ireland receive more than 1,500mm of rain per year. Winter temperatures rarely drop below −5°C. Humidity is high through most of the growing season. It is not California, but it is recognisably the same kind of climate.

Move east or inland and the picture changes. Drier summers, colder winters, and lower annual rainfall make coast redwood a marginal choice. Victorian planters understood this intuitively, even without formal climate data. Giant sequoia, Sequoiadendron giganteum, is hardier and more tolerant of drier conditions, and it dominates the planting record across central and eastern England.

The distinction is still visible today. Arboreta and estates in Surrey, Wiltshire, and East Anglia almost always chose sequoia over coast redwood. The trees are impressive, but they stand on different ecological logic.

Scotland is home to some of the largest giant sequoias on earth outside California. This surprises people who associate Californian trees with warmth. But sequoias in their native Sierra Nevada regularly experience hard winters and heavy snowfall — and they cope. High Atlantic rainfall combined with Scotland's mild growing seasons suits them well.

Benmore Botanic Garden in Argyll has an avenue of giant sequoias planted in 1863. The largest are now over 50 metres tall and more than 3 metres in diameter. The site sits in one of the wettest parts of Britain, in a sheltered valley above the River Eachaig. It is a grove in any meaningful sense of the word.

The Scone Palace grounds in Perthshire and the trees at Cluny Garden in Aberdeenshire are further evidence. Scotland's climate turned out to be one of the more suitable environments for these trees anywhere outside their native range.

Despite a preference for high rainfall, both species struggle in waterlogged ground. They need deep, well-drained soils that retain moisture without becoming saturated. This makes sheltered valley floors — with good drainage from slopes above — a better choice than exposed upland ground, even in the wettest regions.

Shelter from persistent wind matters, especially for young trees. The best-established British groves typically sit in enclosed valleys, on riverside terraces, or within established pinetums where surrounding trees create a modifying microclimate. Exposed hilltop specimens rarely match what sheltered valley sites produce.

Britain provides most of what these trees need. But there are honest absences. The extreme winter cold that suppresses competing species at elevation in California does not occur here. British trees compete with faster-growing native species in ways their Californian counterparts do not.

Scale is also different. The largest British specimens are impressive by any measure, but a redwood in a British arboretum or estate grows within a managed landscape. It does not anchor a grove covering thousands of hectares, or seed naturally into a forest understory. The conditions are right. The scale is not.