Terracotta rhubarb forcers in winter, Grappenhall Heys Walled Garden, Witherwin Avenue, Warrington, Cheshire, England, UK, WA4 3DS

Rhubarb forcers are bell-shaped pots with a lidded opening at the top, used to cover rhubarb to limit photosynthesis. They encourage the plant to grow early in the season and also to produce blanched stems. The pots are placed over two- to three-year-old rhubarb crowns during winter or very early spring. Once shoots appear the lid is taken off, causing them to grow towards the light. Around 18 inches (46 cm) high and 14 inches (36 cm) wide without the lid, they are traditionally made of terracotta but can be as simple as an upside down plastic bucket