2005 Year in Review

28 Degrees: The Damage Point for Rhubarb Plants

Cold temperatures can wreak havoc with several spring crops, none more noticeable than rhubarb. Homeowners then become concerned with the safety of eating the frozen leaves.

“Temperatures right around freezing (32 degrees Fahrenheit) seldom cause any severe problems,” says David Robson, University of Illinois Extension horticulture educator. “It’s when temperatures drop below 28 degrees that damage occurs.”

When temperatures hit the 20s, the cells in the rhubarb petiole (leaf stem) and leaf tissue expand, much like a soda pop in the freezer. The cells rupture, providing no support for the plant. The end result can best be termed “mush.”

As the leaf tissue breaks apart, oxalic acid crystals can move down into the stems. When oxalic crystals are eaten, the throat and tongue can swell, blocking the air passage and causing suffocation. The presence of a high concentration of oxalic crystals in the rhubarb leaves is the main reason they aren’t eaten. There are some crystals in the leaf stems, but not a significant or harmful amount.

Robson says a good rule of thumb to follow after temperatures have fallen into the 20s is to look at the overall health of the plant. If the plant is still standing firm and erect, the leaf stems could still be safely eaten after cutting off the leaf blade.

If the plant is limp and wilting, it’s probably best to avoid eating those stalks. Crystals may have migrated to the stalks. Simply cut the stems off and discard, preferably on the compost pile. New stalks will emerge from below ground, and those will be safe to eat.

But if the plant is questionable, follow the adage of “better safe than sorry” and don’t eat it.

“And if you like to put rhubarb in the freezer to use throughout the year, that’s perfectly safe as long as the plant is healthy to begin with,” says Robson. “Cutting up and freezing rhubarb stalks for cooking does NOT increase oxalic acid crystals since leaves are removed prior to freezing.”

by  Editor, theCity1.com
May 6, 2005