We polish our young birch trunks at this time of year, to bring out the colouring. Older trees are too corrugated to show improvement, but young, smooth bark repays the effort. A gentle scrub with a soft brush will remove winter lichen and greenness, and a hose-down afterwards will leave the trunk sparkling.
The Himalayan birch, Betula utilis var. jaquemontii, is always the most impressive; it is pure, waxy, chalk-white, and the colouring runs out on to the branches (although we draw the line at scrubbing them).
Less conspicuous but more seductive is Betula albo-sinensis var. septentrionalis (no common name, I'm afraid), whose bark is a satin-sheened, coppery pink, reminiscent of Ginger Rogers's legs at their best. We wash them with reverence and admire the glow.