Thalictrum dasycarpum aka Meadow Rue

Thalictrum dasycarpum, or purple meadow rue, belongs to the buttercup family. This herbaceous perennial grows across Canada and the United States. Kew places its range from central Yukon south into the USA. It grows in wet thickets, swamps, meadows, and prairies. It also occurs beside streams and in ditches. Its leaves fall away at the end of the season.

Plants form dense, upright clumps with a light, leafy look. A garden height of 3–5 feet [0.91–1.52 metres] is usual. NC State gives 2–6 feet [0.61–1.83 metres]. RHS lists taller plants, reaching about 8.2 feet [2.5 metres]. Spread can reach 3–4 feet [0.91–1.22 metres]. Growing conditions affect the plant's size. Purple stems branch near the top and are mostly smooth. Compound leaves give the clump its fine texture. Their colour ranges from green to blue-green or grey-green. Each leaf divides into leaflets with two or three lobes. Fine hairs cover the leaf undersides. Leaves become smaller farther up the stems.

Flowers appear from late May through early summer, sometimes into July. The small blooms form branched clusters called panicles. Each flower lacks petals and has greenish-white sepals. These sepals may fall off early. Male and female flowers usually grow on separate plants. Male blooms have hanging stamens with pale yellow tips. Female blooms have slender white pistils that look like petals. Together, the blooms make a pale, airy display. Bees collect pollen from male flowers but do not pollinate them.

Grow this plant in moist soil that drains well. It prefers rich soil with plenty of humus. It accepts full sun or part shade. Dappled afternoon light suits it well in hot weather. Plants in full sun need more water than shaded plants. Hot, humid conditions do not suit it. Sources place it in USDA zones 4–7 and RHS H7. Seed and spring division provide ways to raise new plants. Divisions may take time to settle in.

Use purple meadow rue behind shorter plants in borders. It also suits meadows, wildflower beds, and cottage gardens. Its flowers work well for cutting, and deer tend to avoid it. Tall stems may need stakes, especially in rich soil. Serious pest and disease problems are uncommon. Rust and powdery mildew can occur; dry conditions favour mildew. Slugs may also cause damage. Contact with the leaves can irritate skin. RHS advises gloves and other protection when handling it.