Country diary: rosebay willowherb – a pioneer plant

We walked this stony track to the moors in late summer. Then the banksides were full of upland flowers: St John’s Wort, devil’s-bit scabious, bell heather and sneezewort – small dabs of colour among grass and ferns. Now the eye is saturated by tall swathes of red and orange, the brief autumn flare of rosebay willowherb. Its leaves are a graduation of colours that bleed into each other like pigments leaching from a watercolourist’s brush. Its tops are silver with unfurling seeds. Within a week, these leaves will turn to burgundy as they twist in on themselves before shrivelling to a dull brown.

Rosebay willowherb is a pioneer plant, spreading by windblown seed – 80,000 from just one plant – or by rhizomes marching through the soil. It’s a coloniser on the margins of landscapes, of road verges, woodland edges and wasteland. The downy seeds are carried along railway lines by the draught of trains, along with buddleia, Michaelmas daisy and Oxford ragwort. A coloniser of scorched earth, it was chosen as the county flower of London for its regenerative symbolism after the blitz.

I take home a piece to draw, my pen scrolling across the page, enjoying the curling lines where each seedpod splits into four. Studying these rhythmic shapes makes me appreciate their exuberance. I grow rosebay willowherb in my garden, but in a white form, Chamaenerion angustifolium ‘Album’, instead of the usual pink, its tapering spires graceful against the shadowy trees. A source of nectar and pollen for bees, it’s the food plant for several species of moths, including the small phoenix, the bright-line brown-eye and various hawk moths.

Luckily, I have enough garden space to let loose this vigorous plant. I’m rewarded by elephant hawk moths, Deilephila elpenor, dramatically striped in candy pink and olive green. It’s their plump and wrinkled caterpillars that suggest elephants’ trunks. They also have four striking eye spots and a black “horn” towards the rear. When threatened, a caterpillar retracts its snout, swelling its body and enlarging its eye markings for protection.

Elephant hawk moths pupate in cocoons in leaf litter. I chop up the stems of my willowherb as a garden mulch, a quiet place for the pupae to overwinter before emerging next year as glamorous pink and green moths.