Rumex hydrolapathum aka Great Water Dock

Rumex hydrolapathum is a tall wetland perennial in the Polygonaceae family. Common names include great water dock and horse sorrel. Its native range spans Europe, southwest Siberia and northern Türkiye. It is native to Britain and Ireland. This plant grows in temperate regions, beside ponds, streams and canals. It also grows in bogs and shallow water.

Plants stand upright and form clumps, but their roots spread. Garden plants reach 5–8 feet (1.5–2.5 metres) tall. Their spread reaches about 1.6 feet (0.5 metres). Growth is fast, and plants can reach maturity within one year. The long green leaves taper toward their tips. The plant sheds its leaves each year. Tall flower spikes bear small, pink-tinged green blooms. The RHS gives a July to September flowering season. Chicago Botanic Garden records blooms from July through October. The flowers attract butterflies.

Grow this dock in full sun or partial shade. It needs moist ground or shallow water. It suits pond edges and bog gardens, where soil stays wet. The RHS lists clay and chalk as suitable soils. Choose neutral or alkaline conditions, rather than acid soil. The RHS rates its UK hardiness as H4. Chicago Botanic Garden lists USDA zones 4–8. These ratings come from different regional systems. No pruning is needed, and seed provides a means of propagation.

Its height can add structure beside a pond. Yet its spread can make it hard to manage. It seeds freely and sends new growth from its roots. Once settled, it can be hard to remove. PFAF does not flag it as weedy, unlike the RHS warning. This difference matters when choosing a place for it. Slugs and aphids may attack the plant. The RHS reports few disease problems.

The leaves have a tart, lemon-like taste. PFAF lists cooked young leaves and raw or cooked seeds as edible. Seeds can also be milled into flour, though gathering them is fiddly. Edible does not mean safe in large amounts. The leaves contain oxalic acid, which can reduce calcium uptake. Cooking lowers the acid content. People prone to kidney stones, gout or arthritis should take care. The RHS warns that large amounts can harm people and pets. PFAF records past medicinal uses for roots and leaves. It also records tannin in the roots and their use as tooth powder. These uses do not establish safe or effective treatments.