AP NEWS

Just Ask Us: Can rhubarb become dangerous if exposed to cold weather?

May 6, 2019

Q: Can rhubarb become dangerous if exposed to cold weather?

A: Rhubarb plants as a whole aren’t permanently damaged by cold freezes in the spring, but the edible stalks can be altered by freezing weather in a way that is poisonous to humans, UW-Extension horticulturist Lisa Johnson said.

Rhubarb leaves contain oxalic acid, which is toxic to humans, but that acid is generally not found in the stalks, which is why those are safe to eat. Cold temperatures can change that distribution of oxalic acid, Johnson said.

“Once temperatures fall to a range of the lower to middle 20s, oxalic acid in the leaves will (move) to the rhubarb stalks that we harvest,” Johnson said. “When consumed, oxalic acid can crystallize in the kidneys and cause permanent damage to the organs.”

The rhubarb will show signs of damage when exposed to freezing temperatures, which can warn gardeners harvesting it, Johnson said. The leaves will wilt and blacken along the edges where damaged, and the stalks will be limp with “poor texture and flavor,” Johnson said.

Damaged leaves and stalks should be removed from the plant and discarded.

“It’s safe to harvest rhubarb if the plants show no signs of damage two or three days after the freeze event,” Johnson said.

Any stalks that emerge after the freeze are safe to harvest, Johnson said.

Should you eat any damaged stalks or some of the leaves, you don’t need to rush to an emergency room. National Geographic reports that a person would need to eat several pounds of rhubarb leaves to reach toxic doses.

— Shelley K. Mesch