Rhubarb, also known as pieplant, is an herbaceous perennial grown for its unique, tart flavor of the thick leaf stalks (petioles). Rhubarb sends up its thick, edible stalks early in the spring, a much-anticipated harbinger of the coming growing season. Harvest can begin as soon as the stalks are large enough to cut and continues on through late spring.
You can cut the stalks with a sharp knife, but be careful not to injure any new stalks that are just beginning to poke through the ground. A simple harvesting technique is to grasp the stalk near its base, and pull it down and slightly to one side. About the middle of June or so it is best to give the plants a break for the rest of the growing season so they can produce and store lots of carbohydrates to make a great comeback next year.
Only the leaf stalk of the rhubarb plant should be consumed; the leafy blades contain toxic levels of oxalic acid and therefore are not edible either raw or cooked. Gardeners often inquire whether a frost or a freeze causes the oxalic acid to move into the stalks, rendering them poisonous. There is little evidence that supports the idea of the stalks becoming toxic following a frost or freeze, but the stalks may turn mushy and thus reduce the usability. And it is always best to play it safe.
As spring progresses, many gardeners will notice clusters of flower buds arising on hollow stalks. Flowering and subsequent seed production take much of the food reserves of the plant away from edible stalk production, so it is best to remove the flower stalks as soon as they appear. This unwanted flowering is called “bolting.”
Several factors likely are responsible for bolting in rhubarb, including plant maturity, genetics and environmental conditions. Old-fashioned varieties and seedling volunteer plants may be more prone to flower than some of the more modern cultivars. You can rejuvenate an older, established planting by dividing, and this may reduce the amount of bolting in subsequent years.
But if the bolting persists, you might consider replacing with improved cultivars. Rhubarb is available in either green- or red-stalked cultivars. While red cultivars such as Canada Red, Crimson Red, MacDonald and Valentine seem to be most popular among gardeners, green cultivars such as Victoria (red changing to green) may be more productive.