In culinary use, fresh raw leaf stalks (petioles) are crisp (similar to celery, although they do not share the same family) with a strong, tart taste. Although rhubarb is not a true fruit, in the kitchen it is usually prepared as if it were. Most commonly, the stalks are cooked with sugar and used in pies, crumbles and other desserts. Several varieties have been domesticated for human consumption, most of which are recognised as Rheum x hybridum by the Royal Horticultural Society.
Rhubarb contains anthraquinones including rhein, and emodin and their glycosides (e.g. glucorhein), which impart cathartic and laxative properties. It is hence useful as a cathartic in case of constipation.
Rhubarb is grown widely, and with greenhouse production it is available throughout much of the year. Rhubarb grown in hothouses (heated greenhouses) is called "hothouse rhubarb", and is typically made available at consumer markets in early spring, before outdoor cultivated rhubarb is available. Hothouse rhubarb is usually brighter red, more tender and sweeter-tasting than outdoor rhubarb. In temperate climates, rhubarb is one of the first food plants harvested, usually in mid- to late spring (April/May in the Northern Hemisphere, October/November in the Southern Hemisphere), and the season for field-grown plants lasts until September. In the northwestern US states of Oregon and Washington, there are typically two harvests, from late April to May and from late June into July. Rhubarb is ready to consume as soon as harvested, and freshly cut stalks are firm and glossy.
In the United Kingdom, the first rhubarb of the year is harvested by candlelight in forcing sheds where all other light is excluded, a practice that produces a sweeter, more tender stalk. These sheds are dotted around the "Rhubarb Triangle" between Wakefield, Leeds, and Morley.
The advocate of organic gardening Lawrence D. Hills listed his favourite rhubarb varieties for flavour as Hawke's Champagne, Victoria, Timperley Early, and Early Albert, also recommending Gaskin's Perpetual for having the lowest level of oxalic acid, allowing it to be harvested over a much longer period of the growing season without developing excessive sourness.