Veronicastrum sibiricum

Veronicastrum sibiricum, or Siberian Speedwell, is a tall, spectacular perennial with proud upright mauve flower spikes during the summer. The remarkable foliage is arranged in whorls around the stems. The plant eventually forms a dense clump, which will bring lightness and height to partial shade borders, in moist to wet soil.

The Siberian Speedwell is a plant in the Plantaginaceae family (it was previously classified among the Scrophulariaceae). It also grows in China, Mongolia, Korea, and Japan, where it can be found in ditches along roads, on grassy slopes, or woodland edges. This impressive plant produces tall upright stems, adorned with lanceolate medium green leaves, arranged in successive rings, or whorls, around the stems. Between July and September, each stem produces a mauve-pink "candle" (occasionally white in its natural habitat) at its tip, an elongated, 20 cm (8in) spike of many small nectar-rich flowers with prominent stamens, giving it a very distinctive airy appearance. Overall, the species closely resembles Veronicastrum virginicum, its American cousin, but can be distinguished by slightly wider leaves and a little branched or unbranched inflorescence which accentuates its airy character. In autumn, the foliage turns a beautiful yellow before drying out. In good conditions, the plant will reach between 1.20 and 1.50 metres (4 and 5 feet) high, eventually forming a clump with a diameter of 50 to 80 cm (20 to 32in) after a few years.

Very hardy Veronicastrum sibiricum can withstand temperatures as low as -20°C. It prefers well-drained, rich, and moist, even wet soil. If the soil is too dry in summer, the plant fades and flowering can be compromised. The steep bank of a pond or a sunny border are excellent places to plant speedwell, which still needs several hours of (non-scorching) sun per day. The clump slowly expands through its non-invasive small rhizomes, so give it some space.

Pair it with other lush waterside perennials, such as Ligularia stenocephala, another tall plant, or its low-growing cousin Ligularia dentata 'Desdemona', as well as marsh spurge for a contrast of foliage and colour. You can also play contrast using tall fountain grasses like Molinia arundinacea 'Windsaule'.