You should pick rhubarb when the stems are thick and have reached about 25 to 35 cm (10 to 12 inches) long. Typically, rhubarb is ready to harvest from around April or May, depending on the variety and your location. Early varieties can start cropping from March, while main crop varieties generally start around May. When harvesting, gently twist and pull the stalk from the base of the plant rather than cutting it, to avoid leaving a stub that can rot and invite disease. Only take about one-third of the stalks at a time to keep the plant healthy and productive. The harvesting season usually lasts about 8 to 12 weeks, often ending in late June or early July, allowing the plant time to recover for the next season. You can occasionally pick a few stalks later in summer, but it is best to reduce harvesting by then to avoid weakening the plant. Also, remove and discard the leaves immediately after picking, as they are toxic due to high oxalic acid content. The best harvesting practice is to pick young stalks with fully unfurled leaves, avoiding taking all the stalks at once to maintain plant vigor.