Rosie Lerner, Purdue Consumer Horticulture Specialist
Released 20 May 1999
There's no better way to celebrate spring than with a fresh-baked rhubarb pie, and now is the time to harvest.
Rhubarb is a perennial plant that sends up its thick, edible stalks early in the season. To allow the plants to become established, it's best to wait until the second or third year to harvest from a new planting. However, many gardeners find it irresistible to harvest the first year, and a healthy plant should be able to tolerate a light harvest.
Rhubarb stalks vary somewhat in length, depending on the cultivar, but it is generally advised to allow the stalks to reach 10-15 inches long before harvest. Color of the stalks also varies with the cultivar. Old standby cultivars such as Victoria and Linneaus have green stalks that blush a little red near the base. More recent cultivars, such as Ruby, Valentine and Canada Red, have solid red stalks.
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.
Many rhubarb gardeners will notice clusters of flowers born on hollow stalks. Flowering and subsequent seed production takes much of the food reserves of the plant away from foliage production, so it is best to remove the flower stalks as soon as they appear. Several factors likely are responsible for flowering in rhubarb, including plant maturity, genetics and environmental conditions.
All parts of the rhubarb plant contain oxalic acid, a toxic substance that persists even after cooking. The quantity contained in the leaf stalks (petioles) is small enough to render it safe for eating. However, the leafy blades of the plants have a higher concentration of the oxalic acid, making them poisonous throughout the growing season. Be sure to remove the leafy blades and toss into the compost pile.
Many stories are told that the stalks become poisonous if exposed to frost or freezing temperatures. Although the stalks may become somewhat mushy from freezing, they do not suddenly become poisonous. However, if there is any question of safety, it is probably best to discard.
About the middle of June or so, the rhubarb planting should be given a chance to rebuild its food reserves so it can make a good comeback next year. Discontinue the harvest, apply mulch around the plants to help control weeds and water as needed if weather gets droughty.
Of course, if you find that you absolutely must have a rhubarb pie for your Fourth of July celebration, it won't hurt the plant too much to sneak a few more stalks.
Last updated: 10 April 2006
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