Rheum rhaponticum aka Rhubarb

Rheum rhaponticum, or common rhubarb, belongs to the Polygonaceae family. It is a large herbaceous perennial with leaves that die back. Sources differ on its native range. RHS lists Europe through Siberia and East Asia. Plants For A Future lists southwest Bulgaria and wet mountain rocks. This species may be an ancestor of modern culinary rhubarb hybrids.

Plants reach about 3.3–4.9 feet [1–1.5 metres] tall and wide. They take two to five years to reach full size. A short crown survives winter and sends up spring growth. Dark green leaves have a triangular or heart-shaped outline. Each can reach 1.6 feet [0.5 metres] long. Thick, reddish-green leaf stalks have slight ridges. Upright flower stems rise above the leaves in midsummer. They bear dense panicles of small, greenish-yellow flowers. Reddish-green seeds follow the blooms.

Grow this plant in full sun or partial shade. It needs moist soil that drains well. It accepts chalk, clay, loam, and sand. Acid, neutral, and alkaline soils all suit it. Water during dry summers to keep the soil moist. Add manure mulch in spring, but leave the crown clear. RHS rates its hardiness H6; Plants For A Future lists USDA zones 3–7. Start new plants from seed or divide existing clumps.

The broad leaves give shape to cottage and informal gardens. Plants can also serve as ground cover. Plants For A Future suggests spacing them 5.9 feet [1.8 metres] apart. Remove spent flower stems unless you need seed. Cut off faded leaves at the season's end. Slugs and aphids may attack the plant. Possible diseases include crown rot, honey fungus, and viral infections.

Plants For A Future records raw or cooked leaf stalks as food. Their sour taste suits tarts and other fruit-like uses. It also records unopened flower pouches as edible. Do not confuse edible stalks with the poisonous leaf blades. Cornell identifies anthraquinones and oxalate as toxins in the leaves. It records poisoning in people, goats, pigs, and horses. RHS also warns that ingestion can harm pets. Plants For A Future urges dietary caution for people prone to kidney stones. It records root use as a mild laxative. That record does not establish safe home treatment.