Since comfrey contains pyrrolizidine alkaloids (PAs), which can be toxic to humans and animals, is growing comfrey in the garden safe if it’s near fruits and vegetables, or will the PAs transfer from plant to plant?
Comfrey rejuvenates soil and can prevent fungal and pest problems among your crops. The same alkaloids have antibacterial, antifungal, and antiviral properties when placed on wounds. But don’t eat it! The dangers of PAs are well-documented, as is their potential to persist in animal-based products from livestock that have eaten them. So does the same danger exist within our vegetables?
Is Growing Comfrey in the Garden Dangerous?
Thankfully, no. A study conducted in 2021 and published in the journal Foods asked exactly this: Is horizontal transfer of toxic plant constituents a concern for food safety? Researchers conducted different tests. One involved growing food plants in soil one year after high-PA plants were grown there. Another tested food crops fertilized with compost made from high-PA plants. And a third tested PAs in food crops grown directly adjacent to high-PA plants. The studies showed that growing these high-PA crops only raised the PA content in the soils by a tiny bit, and not in every plot. The third study examined a “worst-case scenario,” where the amount of high-PA plants in the plot far outnumbered the receptor plants. Even then, the transfer rate was 0% to 0.23% – negligible, even though the researchers attempted to simulate the highest concentration possible of high-PA plants. Together, these studies confirmed a few facts that gardeners and farmers can use:
So, growing comfrey in the garden to support soil health and prevent pests within your food garden is a good move. Just don’t eat the plant.
Originally published as “Safely Growing Comfrey Plants” in the Ask Our Experts column of the August/September 2023 issue of MOTHER EARTH NEWS magazine and regularly vetted for accuracy.
