Begin harvesting rhubarb lightly in the plant's second year of growth when the stalks are between 12 and 18 inches tall and are reddish-colored. To harvest the stalks, twist or cut the stalk at the base, taking care not to cut the crown.
From the plant's third year of growth onward, rhubarb stalks are harvested for eight to 10 weeks beginning in the early spring. Harvest the stalks until growth appears to slow, and allow two stalks to remain on each plant to ensure the rhubarb produces in upcoming years. Store the harvested rhubarb in the refrigerator for up to one week before freezing, canning or cooking it.