Comfrey's Mineral Accumulation Process
Comfrey (Symphytum spp.) is known as a 'dynamic accumulator' in permaculture and organic gardening circles. This term refers to its extensive and deep root system, which can reach down up to 10 feet into the subsoil. This characteristic allows it to 'mine' minerals from depths that many other, more shallow-rooted plants cannot reach. Through this process, comfrey draws up a wide array of nutrients, concentrating them in its leaves and roots.
The Role of a Dynamic Accumulator
The function of comfrey as a dynamic accumulator is not about concentrating only one specific nutrient but rather a broad spectrum of them. It is particularly noted for its high levels of potassium, often containing more than composted manure. However, this ability extends to other minerals as well, including calcium, iron, and magnesium. The nutrients stored in the plant's leaves are released back into the soil when they decompose, effectively enriching the topsoil with these vital elements. Gardeners often use comfrey leaves as a nutrient-rich mulch, compost activator, or liquid fertilizer (comfrey tea) to benefit surrounding plants.
Quantitative Analysis of Comfrey's Magnesium Content
While various reports confirm the presence of magnesium in comfrey, specific quantitative data can vary depending on the plant variety, soil conditions, and the part of the plant analyzed. The Feedipedia entry for Russian comfrey provides some concrete figures based on multiple analyses. For fresh aerial parts (the parts above ground), the average magnesium content was found to be 4.3 g/kg of dry matter, with a range from 3.8 to 5.5 g/kg.
Comparison with Other Minerals
To put comfrey's magnesium content into perspective, it's useful to compare it with other minerals also accumulated by the plant. Comfrey is famously high in potassium, with some analyses showing levels as high as 70.1 g/kg of dry matter. This demonstrates that while comfrey does contain magnesium, it is far more significant as a source of potassium. Nonetheless, its magnesium contribution is substantial, especially when used to enrich garden soil over time.
Comparison of Comfrey's Magnesium with Other Plant Sources
| Feature | Comfrey | Spinach | Chard | Kale |
|---|---|---|---|---|
| Magnesium Content | Significant (4.3 g/kg dry matter) | Very high (~79 mg per 100g raw) | High (~81 mg per 100g raw) | Moderate (~33 mg per 100g raw) |
| Mineral Accumulation | Dynamic accumulator via deep roots | Absorbs from topsoil | Absorbs from topsoil | Absorbs from topsoil |
| Toxicity for Oral Use | High risk due to pyrrolizidine alkaloids (PAs) | Generally safe | Generally safe | Generally safe |
| Primary Use | External poultices, garden fertilizer | Culinary (human consumption) | Culinary (human consumption) | Culinary (human consumption) |
This comparison highlights that while comfrey contains magnesium, its suitability for human consumption is not comparable to common leafy greens. The presence of toxic pyrrolizidine alkaloids (PAs) in comfrey means it should not be ingested. Therefore, for individuals seeking dietary magnesium, common vegetables like spinach and chard are safer and more effective sources. Comfrey's strength lies in its ability to enrich soil and serve as an organic fertilizer, not as a food source.
The Risks Associated with Oral Comfrey
The high concentrations of toxic pyrrolizidine alkaloids (PAs) found in comfrey, particularly in the roots, pose a serious health risk if ingested. These compounds can cause severe liver damage and have been linked to liver cancer. This has led to the banning of oral comfrey products in many countries, including a recommendation by the US FDA to remove them from the market. The risks are substantial enough that internal use is never recommended. While topical use on unbroken skin is considered possibly safe for limited periods, it is always advised to consult with a healthcare professional before use, as PAs can still be absorbed through the skin.
Safe and Practical Uses of Comfrey
Despite the risks of internal consumption, comfrey is a highly valuable plant for gardeners and as a livestock feed. Its benefits are best realized through safe, external, and agricultural applications. The leaves and roots are rich in nutrients, making them excellent for composting and creating nutrient-rich liquid feeds for other plants. Comfrey tea, made by soaking the leaves in water, is an easy and effective fertilizer. Externally, the mucilage-rich leaves have historically been used in poultices for bruises, sprains, and skin irritations, with allantoin promoting tissue healing.
Conclusion: The Final Verdict on Comfrey and Magnesium
In summary, is comfrey high in magnesium? The answer is a qualified 'yes.' Comfrey is a dynamic accumulator that concentrates a variety of minerals, including magnesium, in its tissues. Scientific analyses confirm that it contains a significant amount of magnesium, alongside high levels of other nutrients like potassium and calcium. However, this does not mean it is a suitable dietary source for humans due to the presence of liver-toxic pyrrolizidine alkaloids. Its value lies in its role in the garden and as a feed source for livestock (where toxicity is managed), not in human consumption. Anyone seeking dietary magnesium should opt for safer, more traditional sources like nuts, seeds, legumes, and leafy greens. For gardeners, comfrey remains an exceptional natural fertilizer for enriching the soil and promoting plant health.
Note: The content of this article is for informational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before using any herbal product.
References
- Feedipedia. (2012). Russian comfrey (Symphytum × uplandicum). https://www.feedipedia.org/node/12540
- Healthline. (2025). Comfrey: Uses, Benefits, and Risks. https://www.healthline.com/health/what-is-comfrey
- NCBI Bookshelf. (2022). Comfrey - LiverTox. https://www.ncbi.nlm.nih.gov/books/NBK548370/
- WebMD. (2025). Comfrey - Uses, Side Effects, and More. http://www.webmd.com/vitamins/ai/ingredientmono-295/comfrey
- Herbal Reality. (2024). Comfrey | Herbs. https://www.herbalreality.com/herb/comfrey/
- Red Pond Farm. (2024). Comfrey: The Ultimate Permaculture Superplant. https://redpondfarm.com/comfrey-the-ultimate-permaculture-superplant/
- Alberta Urban Garden. (2015). Comfrey an Organic Fertilizer and Mineral Accumulator you… https://www.albertaurbangarden.ca/2015/02/22/1230/
Comfrey Fact Sheet - Living Herbs details its rich nutrient profile, including magnesium, and traditional uses.
Key Takeaways
- Magnesium Source: Comfrey contains significant levels of magnesium, though specific amounts can vary based on soil and plant part.
- Dynamic Accumulator: Its deep root system allows it to pull nutrients like magnesium and potassium from the subsoil, enriching the topsoil when the plant decomposes.
- No Oral Consumption: Due to toxic pyrrolizidine alkaloids (PAs) that cause liver damage, comfrey should never be taken orally by humans.
- Safe Uses: The plant is best used externally for poultices on unbroken skin or in gardening as a compost activator, mulch, or liquid fertilizer.
- Potassium over Magnesium: While it contains magnesium, comfrey is a much more notable accumulator of potassium.
FAQs
Q: Is comfrey a good source of dietary magnesium for humans? A: No, comfrey is not safe for human consumption due to toxic pyrrolizidine alkaloids, which can cause severe liver damage and cancer.
Q: How do gardeners use comfrey to add magnesium to their soil? A: Gardeners can use comfrey leaves as a nutrient-rich mulch, chop and drop them in the garden, or make a liquid fertilizer (comfrey tea) to enrich the soil with accumulated minerals like magnesium.
Q: What are pyrrolizidine alkaloids (PAs)? A: Pyrrolizidine alkaloids are toxic compounds found in comfrey that can be harmful to the liver and lead to serious health issues, especially when ingested.
Q: Can topical comfrey products be used safely? A: Topical comfrey creams or ointments can be used cautiously on unbroken skin for limited periods, typically less than 4-6 weeks. They should never be applied to broken or damaged skin, and consulting a doctor is recommended.
Q: Is comfrey high in other minerals besides magnesium? A: Yes, comfrey is particularly high in potassium, but also contains other minerals such as calcium, iron, and a range of vitamins, including A, C, and B12.
Q: Are all types of comfrey toxic? A: Yes, both common comfrey (Symphytum officinale) and Russian comfrey (Symphytum x uplandicum) contain toxic pyrrolizidine alkaloids. The concentration can vary depending on the plant part, with roots generally containing higher levels.
Q: What is a dynamic accumulator? A: A dynamic accumulator is a plant, like comfrey, with deep roots that can pull nutrients from the subsoil, concentrating them in its leaves and ultimately enriching the topsoil when the plant material decomposes.
Q: How does comfrey compare to other plants in magnesium content? A: While comfrey contains a notable amount of magnesium, safer edible plants like spinach and chard are better sources for human dietary needs. Comfrey's primary benefit is for soil enrichment.
Q: What are the main benefits of using comfrey in a garden? A: In addition to enriching the soil, comfrey can be used as a compost activator, a high-nutrient mulch, and a feed for some livestock, provided proper precautions are taken due to its toxicity.
Q: Can comfrey be used as a safe substitute for magnesium supplements? A: No. Given the serious liver toxicity risks associated with internal use, comfrey is not a safe alternative to commercial magnesium supplements.
Q: What are the primary concerns with using comfrey? A: The main concern is the risk of liver damage and potential cancer from ingesting the pyrrolizidine alkaloids present in the plant. This is why oral use is strictly prohibited.
Q: Why is comfrey still used despite its toxicity? A: Comfrey's deep roots and ability to accumulate minerals make it a valuable resource for enriching soil and as an effective external remedy for minor skin and muscle issues when used correctly and on unbroken skin. Its benefits are reaped in safe, non-ingestible applications.
