Veronicastrum sibiricum aka Culver's Root

Veronicastrum sibiricum is a perennial called Siberian Culver's root. It belongs to the plantain family, Plantaginaceae. Its native range runs from Siberia to northern China and Japan. It also grows in Korea and Russia's Far East. Wild plants grow in grassland, on slopes, and in thickets. They occur in both mountain and lowland sites. In northern China, records place it below 8,200 feet [2,500 metres].

This plant forms upright clumps and grows from rhizomes. Garden plants reach about 3.3–5 feet [1–1.5 metres] tall. Their spread reaches about 1.6–3.3 feet [0.5–1 metre]. Strong stems hold narrow, lance-shaped leaves in rings, called whorls. The leaves fall as the growing season ends. Plants take two to five years to reach full size. The tall form suits the back of a flower bed.

Slender spikes bear many small purple or lavender flowers. Smaller spikes branch from the sides of the main spike. Together, these branches give the flower heads a tiered shape. Chicago Botanic Garden describes flowers opening from the top downward. Its account gives July to September as the flowering season. Its bloom calendar extends that season into October. Butterflies visit the flowers. The flower spikes add height to borders and cottage gardens. Groups also suit woodland edges and prairie-style plantings. A single plant can serve as a specimen in beds.

Grow it in sun or partial shade, with moist soil. It needs good drainage rather than ground that stays waterlogged. Humus-rich soil with moderate fertility suits it well. It accepts chalk, clay, loam, and sand. It also grows in acid, neutral, or alkaline soil. RHS gives it an H7 hardiness rating. Chicago Botanic Garden lists USDA zones 4–9. Cut old stems back in early spring. Divide clumps in spring, or sow seeds in autumn. Use pots in a cold frame for autumn sowing.

Care needs are low, though pests and disease can occur. Aphids may attack plants, and leaf spot can affect foliage. Downy mildew and powdery mildew are other possible problems. Wet soil with poor drainage may lead to root rot. No edible uses or known hazards appear in PFAF's account. That does not establish safety for people or pets. PFAF records traditional Korean use of roots for colds. It also records their use as a liver tonic. These records describe medicinal use, not proof of treatment benefits.