Grown for the tart flavor of its edible stalks, rhubarb (Rheum x cultorum) is a staple cool-season crop that grows in U.S. Department of Agriculture plant hardiness zones 3 through 8. It is picked primarily in spring when the stalks taste best, but can be harvested into summer. Consider other factors, too, when harvesting rhubarb, including the plant's age and the appearance of the leaves and stalks.
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Rhubarb takes three years to mature and its stalks should not be harvested during its first two years in the garden. Harvest your first crop of rhubarb over a four-week period in early spring of its third year. From fourth year onward, harvest the leaves for eight to 10 weeks in spring.
What to Look For
Rhubarb stalks provide clues about when to harvest with their size and color. Harvest-ready stalks are 10 to 15 inches long with a diameter of 1/2 to 1 inch (Ref 3, "Rhubarb"). Varieties such as "Canada Red" (Rheum x cultorum "Canada Red") develop a red stalk at maturity while "Victoria" rhubarb (Rheum x cultorum "Victoria") has a speckled stalk that fades to green at the tip.