Fresh field-grown rhubarb is sold in long, crisp, red or pale pink stalks in the late spring and early summer. Hot house-grown rhubarb is available year-round in some regions. Before the crop reaches market, the leaves are trimmed from the stalks and discarded since they contain high amounts of toxic oxalic acid. Although tart rhubarb is technically a vegetable, it is cooked and sweetened like a fruit. Combining rhubarb with strawberries is a popular pairing. The flavors are pleasantly contrasting, and the berries help sweeten the rhubarb.