The below freezing temperatures across much of Iowa last week has caused some gardeners to question the edibility of their rhubarb. Their concern is that the poisonous oxalic acid in the leaf blades has moved down (leaked) into the stalks upon exposure to freezing temperatures. The movement of large amounts of oxalic acid into the stalks is high unlikely. Rhubarb is a cold tolerant plant and generally is not damaged by a light freeze. A hard freeze will damage the plant. Gardeners should examine their rhubarb after exposure to freezing temperatures and base their harvest decision on plant appearance. If the stalks and foliage are undamaged, the rhubarb is fine and may be harvested. If the leaves have shriveled and turned black and the stalks have become soft, the badly damaged stalks should be pulled and discarded. New stalks which emerge later in the season are safe to eat. If only the margin (edge) of the leaf has been blackened, the rhubarb should be safe to eat.
This article originally appeared in the May 4, 1994 issue, p. 62.