Colutea arborescens aka Bladder Senna

Colutea arborescens, or bladder senna, is a deciduous shrub. It belongs to the bean family, Fabaceae. Its native range covers central and southern Europe. It grows in open woods and along roads and railways. These sites often have lime-rich soil. The shrub grows fast and forms a rounded, bushy shape. Several stems make a broad mound with a coarse texture.

Garden height varies between sources. NC State gives 6–10 feet [1.8–3 metres] across its descriptions. RHS lists height and spread of 8–13 feet [2.5–4 metres]. Its shorter description puts height near 10 feet [3 metres]. The leaves are green, with a pale or bright tone. Each odd-pinnate leaf has nine to thirteen leaflets. The leaves feel rough and give little autumn colour. The shrub sheds them for winter.

Yellow, pea-like flowers grow on the current season's shoots. They open in spring, with May noted by NC State. A few flowers may keep appearing through summer. Bees visit the blooms, which grow in racemes. Inflated seed pods follow and give bladder senna its name. These legumes reach about 0.26 feet [0.08 metres] long. Their colours can include green, pink, bronze and purple. The pods add interest after the main flower display.

Grow this shrub in full sun and well-drained soil. It accepts clay, loam, sand, chalk and rocky ground. It also grows across acidic, neutral and alkaline soils. Poor, dry soil and exposed sites suit it. It tolerates drought but fares poorly in hot, humid conditions. Dry to moderately moist soil meets its water needs. NC State lists USDA zones 4–8; RHS rates it H6. RHS gives ten to twenty years to reach full size. Seeds and softwood cuttings provide ways to raise new plants.

Bladder senna suits borders, informal gardens, hedges and screens. Its roots help hold banks and limit soil loss. It also fixes nitrogen and attracts wildlife. Care needs are low, with few major pest or disease problems. Pruning in late winter or early spring can check growth. NC State warns that it can spread aggressively in some places. PFAF records no known edible use. The seeds are poisonous and can cause vomiting if eaten. Past medicinal uses include laxative and diuretic treatments made from leaves. PFAF describes those effects as unreliable, so this is not an edible crop.