Lacking lid (often the norm with older forcers) This is one of a number of forcers from the same source - Search "Forcer" to see remaining stock.. No head-gardener of any Country Estate would have had a walled garden without rhubarb and seakale forcers. Used to cover rhubarb to limit photosynthesis, they encourage the plant to grow early in the season and ultimately produce long blanched stems. The pots are placed over two- to three-year-old rhubarb crowns during winter into early spring. Once shoots appear the lid, or tile, is taken off, causing them to grow towards the light.