Rhubarb, Rheum rhaponticum, is a popular vegetable grown for its edible petioles (leaf stalks) which are tart and used for making jams, jellies and especially pies. The leaves of rhubarb are large and showy in the garden, but they are inedible because of oxalic acid and oxalate content which can cause poisoning.
"When a hard frost or freeze occurs in the early spring, rhubarb plantings are often damaged," explains Tony Bratsch, University of Illinois Extension horticulture educator. "Covering plants with floating row covers, sheets, blankets, straw or tarps provides some degree of insulation; but if temperatures fall to the mid-20s, these protective covers reach their limitations, and plant damage occurs."
In response to low temperatures, oxalic acid increases in rhubarb stalks as leaf tissues begin to freeze. To determine if freeze damage has occurred to your plants, the leaf tissue will initially appear "water soaked" soon after the cold event, and then wilt, and after a few days will eventually dry and blacken along the edges or where tissue was damaged. If there is no evidence of leaf damage, then the stalks are considered safe to eat.
"Do not eat wilted or limp stalks from obviously frostbitten plants," advises Bratsch. "Remove injured leaves and stalks, and discard or add to the compost pile. Eventually, a new set of leaves will emerge, and no permanent damage is done to the plant. A mature plant should yield another crop of stalks within four to six weeks."
For more information about rhubarb, check out the April issue of The Green Thumb. You'll find it on our SI Gardening website, http://web.extension.uiuc.edu/regions/hort.
Source: Tony Bratsch, Extension Educator, Horticulture
Source: Anthony Bratsch, Extension Educator, Horticulture (Serving East-Central and Southeastern Illinois), firstname.lastname@example.org
Pull date: April 10, 2009