Is rhubarb safe to eat after a frost? (Main risks)

In this brief guide, we will answer the question “Is rhubarb safe to eat after a frost?”. We also will discuss the uses of rhubarb and its health benefits.

Is rhubarb safe to eat after a frost?

Yes, rhubarb remains safe to eat after being subjected to frost, provided it hasn’t been damaged. Rhubarb is quite resilient, with its leaves enduring temperatures as low as three or four degrees below freezing without harm. The sturdy rhizome and crown can endure extended periods in frozen or very cold, dry soil without suffering from cold-related damage or desiccation. (1)

Why frost frost-damaged rhubarb can be dangerous?

Frost-damaged rhubarb can be dangerous as freezing stress can cause oxalic acid in the leaves to migrate into the stalks.  In the early spring when rhubarb starts to grow, it’s common for emerging growth and new leaves to be affected by frost. It’s important to remove and dispose of any leaves damaged by frost. The soluble oxalates present in fresh leaves and frosted stalks can be toxic to humans. (2)

What are the dangers of oxalic acid?

Oxalic acid presents a kidney-related threat and possesses corrosive properties. The lethal dose of oxalic acid varies with age but typically falls within the range of approximately 10 to 25 grams.

When oxalate combines with calcium in the bloodstream, it forms insoluble calcium oxalate, which can potentially lead to severe hypocalcemia and involuntary muscle contractions. On average, rhubarb leaves contain around 0.5% oxalic acid, along with higher levels of non-toxic malic acid.

Extended consumption of rhubarb can pose challenges for individuals with kidney disorders, gout, and rheumatoid arthritis, as oxalic acid can disrupt essential nutrients.

Oxalic acid can also interact with metal ions such as Ca2+, Fe2+, and Mg2+ to create deposits of corresponding oxalates, which may irritate the gastrointestinal tract and kidneys. The lethal dose (LD50) for oxalic acid for a person weighing 65 kg, would be 25 grams.

Symptoms of rhubarb poisoning encompass abdominal pain, diarrhea, persistent and severe vomiting, followed by internal bleeding, convulsions, and, ultimately, a coma. (3, 4)

How is rhubarb cultivated?

Rhubarb stalks can be harvested as early as mid to late spring in temperate climates, with field-grown varieties continuing to be accessible until September  When freshly picked, rhubarb stalks exhibit a firm and glossy appearance, making them ideal for consumption.

Rhubarb is a highly adaptable vegetable, thrives in various regions and remains available for a significant portion of the year, thanks to greenhouse farming.

The roots of rhubarb plants are typically harvested from those that have reached the age of four or older, typically during October. The roots are carefully cleaned and undergo a thorough drying process. Once completely dried, the rhubarb root is finely ground into powder and securely stored in a sealed container. (4)

How is rhubarb harvested and stored?

Rhubarb is harvested by gathering the stalks above ground and removing the leaf blades. After this, the stalks undergo an initial processing phase. When harvesting the stalks, there is always a risk of bruising the delicate tissues, which could potentially lead to lower moisture levels in the petioles later on.

Preserving rhubarb’s freshness requires storing it in a cool, humid place. Temperatures between 32 to 40 °F (0 to 4°C) with around 95% relative humidity are ideal for rhubarb preservation.

However, maintaining both the necessary cold and moisture can prove challenging, as refrigerators provide the cold but often dry out the air inside. As an alternative method wrapping the stalks completely in aluminum foil helps them to keep hydrated for longer. (5)

How to use rhubarb?

Rhubarb can be used in both culinary and medicinal contexts. The nutrient-rich petioles are frequently employed as a vegetable after cooking, serving various culinary purposes. Rhubarb features a wide array of culinary creations, including juices, pickles, salads, sauces, jams, and sweet pies.

While the petioles are appreciated for their nutritional value, the dried rhubarb rhizome or root also possesses significant medicinal properties. In Traditional Chinese Medicine, rhubarb is recommended for addressing conditions like fever, constipation, abdominal pain, appendicitis, kidney issues, liver cancer, and hypertension.

The dried rhubarb root has been traditionally employed as a potent cathartic agent, and its laxative effects are well-documented, with some believing it may aid individuals dealing with obesity in their weight loss efforts.  (6)

Conclusion

In this brief guide, we answered the question “Is rhubarb safe to eat after a frost?”. We also discussed the uses of rhubarb and its health benefits.

In my studies, I was able to find out that there is no problem in consuming rhubarb after a frost as long as there is no damage to the plant. In case of cold damage,  the plant does become toxic and should not be consumed. Its leaves are poisonous and frost stress makes its toxins migrate to the stalks

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