Rhubarb is a popular perennial vegetable known for its tart stalks, which are frequently used in pies and jams. While the stalks are safe for consumption, the large, dark green leaves attached to them are not. These leaves contain toxic compounds that can cause severe illness in humans and animals, making their safe disposal a necessity. Following proper handling procedures is the first step in managing your rhubarb harvest responsibly.
The Toxicity of Rhubarb Leaves
The danger within rhubarb leaves comes from oxalic acid, which is present in a much higher concentration in the foliage than in the edible stalks. Oxalic acid, also found in lower amounts in foods like spinach and kale, is a colorless compound that is toxic when ingested in large quantities. The concentration of this acid in the leaves is typically around 0.5 to 1.0% of the total leaf weight, a high level that necessitates caution.
When consumed, oxalic acid binds with calcium in the bloodstream, forming insoluble calcium oxalate crystals. These microscopic, sharp crystals cause immediate, painful symptoms, including a burning sensation in the mouth and throat, nausea, and vomiting. The removal of calcium from the body’s circulation can also lead to a drop in blood calcium levels, causing severe symptoms such as muscle twitches, numbness, and convulsions.
The most serious health concern is the effect of these crystals on the kidneys, which filter them from the blood. The accumulation of calcium oxalate in the renal tubules can obstruct normal function, potentially leading to kidney damage or acute kidney failure. While a fatal dose for an adult requires consuming a large amount of leaves, small children and pets are much more vulnerable. Cooking or boiling the leaves does not break down the oxalic acid to a safe level, meaning consumption should be avoided.
Recommended Safe Disposal Methods
Handling rhubarb leaves requires a cautious approach to ensure the toxic material is kept away from people and animals. After separating the leaves from the stalks immediately upon harvest, wash your hands thoroughly to remove any plant residue. The leaves should be disposed of in a manner that prevents accidental ingestion and allows for the eventual breakdown of the toxic acid.
One of the simplest and safest methods is disposal through municipal waste collection. Small quantities of leaves can be placed into a sealed plastic bag and deposited into the trash bin. This method ensures the material is quickly removed from the property and sent to a landfill, eliminating the risk of exposure to children or pets.
For gardeners who prefer to recycle organic materials, composting is a viable option, as the oxalic acid breaks down during decomposition. Microorganisms within a healthy compost pile are effective at breaking down the acid over time, neutralizing the toxicity. To aid this process, the leaves should be chopped into smaller pieces before being added to the pile. Avoid using the leaves in vermicomposting, or worm bins, because the oxalic acid can be harmful to the composting worms.
If you choose to compost, ensure the leaves are buried deep within a hot, active pile. The final compost product should be fully matured before use in vegetable gardens to prevent premature exposure to the decomposing material.
Addressing Non-Food Applications
The toxicity of rhubarb leaves has led to the idea that a boiled extract can serve as a natural pesticide or insecticide. This traditional use relies on the presence of oxalic acid, which can deter or eliminate pests like aphids and spider mites. A solution is typically made by boiling the leaves in water, straining the liquid, and then adding soap to help the mixture adhere to plant surfaces.
While this application is widely discussed, it is not without risk and is not recommended for use on edible plants. The resulting spray should be clearly labeled as poison and kept away from children and pets, as the toxic compounds remain in the liquid form. The effectiveness can vary greatly, and the need for extreme caution makes it an impractical solution for most home gardeners.
Beyond pest control, the leaves have a couple of niche, non-ingestible uses. The large size and durable nature of the leaves make them suitable for temporary use as a weed barrier or ground cover in garden beds. They can also be used in historical cooking methods as a steaming wrapper, similar to cabbage leaves, but the food must never touch the leaf surface. Another application is extracting the tannins from the leaves to create a natural yellow or green dye for fabric or paper.