The leaves are the poisonous part of the rhubarb plant. The stalks, which are the colorful red and green stems, are perfectly safe to eat raw or cooked. The large, flat leaf blades that fan out from the top of each stalk contain toxic levels of oxalic acid and should never be eaten.
Why Rhubarb Leaves Are Toxic
Rhubarb leaves contain two harmful substances: oxalic acid and possibly anthraquinone glycosides. Oxalic acid is the primary concern. While the stalks also contain small amounts of oxalic acid, the concentration in the leaf blades is far higher, enough to cause serious harm if eaten in quantity.
When you consume a large amount of oxalic acid, it binds to calcium in your blood and tissues, forming tiny crystals of calcium oxalate. These crystals deposit in soft tissues throughout the body, with the kidneys being especially vulnerable. The drop in available calcium can also disrupt normal muscle and nerve function, since your body depends on circulating calcium for both. Research on oxalate poisoning has shown that elevated oxalic acid in the blood leads to measurably reduced calcium levels, driven largely by this crystal deposition rather than simple excretion.
Symptoms of Rhubarb Leaf Poisoning
Eating rhubarb leaves can cause burning and irritation in the mouth and throat, nausea, vomiting, and abdominal pain. In more serious cases, the drop in blood calcium and the buildup of oxalate crystals in the kidneys can lead to difficulty breathing, seizures, and kidney failure. Fatal cases have been documented historically, though they are rare because the leaves taste unpleasant enough that most people stop eating them quickly.
The amount of leaves needed to cause life-threatening poisoning in an adult is substantial. Estimates vary, but most sources suggest you would need to eat several pounds of raw leaves to reach a lethal dose. That said, smaller amounts can still cause painful gastrointestinal symptoms and kidney stress, particularly in people with existing kidney problems.
Cooking Does Not Make the Leaves Safe
A common question is whether boiling or cooking rhubarb leaves breaks down the toxins enough to make them edible. It does not. Cooking does not wash out oxalate from foods that are high in oxalate and calcium, which includes rhubarb leaves. No preparation method, whether boiling, steaming, or baking, reduces the oxalic acid content enough to make rhubarb leaves safe for consumption.
Are the Stalks Safe After a Frost?
Gardeners sometimes worry that a late frost or freeze could cause oxalic acid to migrate from the leaves down into the stalks, making the stalks poisonous too. According to Purdue University’s plant pathology department, there is little evidence to support this idea. However, researchers acknowledge that they don’t fully know whether oxalic acid moves from the leaf blade into the stalk during a freeze, or whether any such movement would reach dangerous concentrations.
In practice, most rhubarb growers harvest stalks in spring and early summer, well before fall frosts. If your rhubarb has been hit by a hard freeze, the stalks often become soft and mushy anyway, making them unappealing to eat. If the stalks still look firm and healthy after a light frost, they are generally considered safe, but discarding any that appear damaged or wilted is a reasonable precaution.
How to Safely Harvest and Prepare Rhubarb
When harvesting rhubarb, grip the stalk near the base and twist it free from the plant. Cut the leaf blade off at the point where it meets the stalk and discard it. You can compost the leaves safely, as the oxalic acid breaks down during decomposition and won’t harm your garden soil.
The stalks themselves are versatile in the kitchen. They’re most commonly stewed with sugar for pies, crumbles, and jams, but they can also be roasted, pureed into sauces, or eaten raw if you enjoy their sharp, tart flavor. The color of the stalk, whether deep red, pink, or green, has no bearing on safety or toxicity. All stalk colors are equally safe to eat. Greener stalks simply tend to be more tart, while red stalks are slightly sweeter.