Comfrey fertilizer has long been touted as a miracle by permaculture enthusiasts for its soil-boosting properties. Does it really heal damaged soil? Let’s weigh the research.
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Growing your own comfrey fertilizer is all the rage.
I first learned about this permaculture super plant as a permaculture design student over 10 years ago. I wondered if it really lived up to the hype, so I planted it prolifically around my garden and edible landscape.
I’m always up for an experiment, and let me tell you, I was surprised by how quickly comfrey fertilizer enriched and improved my compacted clay soil!
What is (supposedly) so amazing about comfrey fertilizer?
This herb is known for its role in harvesting nutrients from the soil and accumulating generous quantities of nitrogen, phosphorus, potassium, potash, and calcium.
The theory behind comfrey fertilizer is that the roots reach down into the soil, similar to a dandelion root. Along the way, they break up compacted soil and enrich it as the roots die back and decompose.
In addition, nutrients are thought to accumulate in the leaves, which can be chopped and dropped several times per year as a nutrient-rich green mulch.
Does the theory about comfrey fertilizer hold up in research?
Some researchers actually disagree with the accolades given to comfrey fertilizer. Robert Pavlis, a biochemist and Master Gardener, has collected research that shows comfrey does not contain any more nutrients (dry weight value) than other popular fertilizer plants, such as alfalfa or clover. In fact, comfrey’s nutrient levels were pretty average.
Compared to animal manures, comfrey values of NPK are relatively low. However, its nutrients are more immediately bioavailable to plants, especially in liquid form.
Meanwhile, one permaculture practitioner took soil samples over time on his urban farm, to see how the comfrey fertilizer theory stood up to his compacted clay soil: Did it improve his soil?
After 5 years of growing comfrey, the topsoil in this sample shows… higher percent organic matter than any of the previous samples, and the nutrient levels are practically off the charts – a 47 to 232% increase over the previously observed highs.
… just on the basis of NPK the comfrey is completely vindicated.”
Here are his soil test results.
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The Limitations of Laboratory Results
Personally, my opinion of comfrey fertilizer remains firmly in the positive, even while I respect the outcome of the laboratory results. In other words, I believe that both the laboratory results and the citizen science results are correct and hold value.
To illustrate how both can be correct, I refer to the work of Dr. Christine Jones, an Australian soil ecologist. According to her, “much of the agricultural research undertaken in pots in glass houses is fundamentally flawed.”
More succinctly, NPK dry weight values of plant matter don’t tell the whole story.
Many laboratory studies use sterile environments that are unable to demonstrate what happens when soil organisms participate in the process of nutrient acquisition and uptake.
Science is only just beginning to develop the tools for studying the role of root exudates and soil microbes in biochemical processes.
Is Comfrey a Garden Cure?
Ultimately, comfrey fertilizer may have average nutrient levels. What everyone seems to agree on, however, is that this herb is fast-growing. It provides A LOT of biomass in the small space that one plant occupies in the garden.
Popular cover crops, like clover and alfalfa, must be grown over the ENTIRE garden to provide the same amount of nutrient-rich biomass that a few comfrey plants can provide. And as a perennial, comfrey keeps giving year after year.
What’s more, comfrey roots and the rapidly decomposing leaves appear to increase microbial activity and accelerate soil-building.
When it comes to a plant that:
- provides non-stop biomass in a small space (multiple cuttings per growing season)
- is perennial
- suppresses weeds
- attracts bees and other beneficial insects
- conditions soil
- accelerates microbial activity
…the role of comfrey in the garden (per square foot) is unparalleled.
I encourage you to read up on growing comfrey and become your own scientist to see for yourself! I recommend planting Bocking 14 root cuttings.
Then, when you’re ready to make your own comfrey fertilizer, check out 7 comfrey uses in the permaculture garden.
Have you noticed any improvements in your garden after adding comfrey fertilizer?
Gabriel Palmer says
Hi I would like to know if this plant need direct sun or shady places , I live in a tropical country . Thank you
Kat Mei-Leign says
If grown in the shade the leaves are softer and darker than grown in sun light. I live in the NE US and the plant loves wet soil and is an over all great looking plant along with it’s wonderful properties.
Comfrey will do best in partial sun/shade with moist soil. It can tolerate sunny and dry conditions, but will not thrive there as much.
jesse w ulery says
So you pose a question. Fail to answer in the article. Provide link to yet another article that once again promises to answer the question. I call click bait. Won’t be back, sorry.
Jim Basion says
OH no. I hope the world can somehow go on.
Diane Murray says
Why Bocking 14 versus any other variety of comfrey?
Great question. True comfrey (Symphytum officinale) is quite dispersive. Russian comfrey, on the other hand, aka Bocking 14 (Symphytum x uplandicum) is most often chosen because it has sterile seeds and only reproduces by expanding at the root level, which can be divided after a few years. You can read more about comfrey on my post What is Comfrey and How to Grow It.
Diane Murray says
Thanks for your reply. Comfrey has been growing in the yard/garden of the house I bought 15 years ago but it was only this year that I identified it. This variety definitely grows by root division, not seeds — otherwise the plant would be all over the place by now. In its current location the plants are crowded so can I divide it in the fall? Do you know if deer eat comfrey? It would be nice to grow some outside the fence.
I cut it back about 10 days ago because the leaves had pale grey spots (maybe some kind of mildew?). Now it’s growing new fronds and is fixing to bloom again. The flowers are dark(ish) purple and the bees love them. Is the color of flower distinctive to the variety? (Bocking 14 versus some other kind).
I just put some leaves into the dehydrator. I’m going to follow your recipe for comfrey salve and perhaps make lotion as well. Thanks for posting the salve recipe.
Do any of your previous articles discuss comfrey as food or medicine for human use? Thanks.
Yes, divide in fall. Deer may munch occasionally, but comfrey is more medicine than food for them. Flower color does not seem to indicate variety in my experience.
Emma Cooper says
I love having comfrey in my garden. The flowers are a magnet for bees, and I use it to make a potash-rich feed for my tomatoes and peppers. They seem to do well on that diet, so I am happy 🙂 Thanks for sharing.
My community garden plot (which is farmer-tilled every year 🙁 ) has volunteer comfrey that in three years has not flowered. I do use the older leaves as compost and weed suppression around the other veggies, though. New this year are leaves that have become beautifully lobed. I am starting to wonder whether it is actually comfrey.
It would be hard to identify comfrey without a photo, but even if it isn’t comfrey, it sounds like this “weed” is providing something that the soil needs 🙂
Petra Kaye says
Beware the comfrey invasion. We have just spent an hour in our patch digging out the stuff, and have only scratched the surface. It is very invasive in some situation – looks great, but takes up precious space.
Yes, if you have true comfrey, it will spread from seed in many growing zones. I had 12 plants of true comfrey and in 10 years I only found a handful of plants started elsewhere in the garden because I frequently cut it back so the flowers can’t set seed. That’s why I recommend Russian comfrey.
Judith Janes says
I can attest to comfrey’s healing properties. My husband was building a protected entry for our house’s front door and using cedar shingles to side it. He barked his shin on a pile of cedar shingles; since cedar is toxic it got infected and would not heal up. Neosporin wouldn’t touch it. I grabbed my herb book for a solution, and purchased dried comfrey root from the health food store, which I made into a poultice for his leg. Two applications, and his leg healed up beautifully. It really works!
Cool! Thanks for sharing!
Patricia Mumme says
Never plant it where you will till or disturb the soil. Every little bit of root will produce a new plant, and you will never get rid of it without strong weedkillers. It will spread so don’t plant it around your compost pile. Roots will get into the compost, and you will spread root pieces when you spread compost. Then you have a problem. Best to plant it next to a building or in an area that you mow around completely, and NEVER plan to plant anything else there. I am talking about Russian comfrey. It does not spread by seed, thankfully, but you MUST be very vigilant about the roots spreading. It is irresponsible of this article not to warn about that.
Hi there! Welcome to our community here at Tenth Acre Farm. If you’d like to read more information about comfrey (including warnings), you’ll find it in my article What is Comfrey and How to Grow It. Comfrey has many uses around the garden, and sometimes spreading is celebrated. Planted in certain climates, spreading is negligible. As in all things permaculture, it depends.
Seems like there is some scientific evidence for the use of comfrey as an anti-inflammatory and to speed healing but also some evidence it is carcinogenic. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5894094/
It does grow fast and can produce mulch, but wood chips seem to be a better source of mulch if you have access. As for claims that it has deep roots and pulls up nutrients, seems dubious and it takes up a lot of garden space for little other utility. I’m planning to try to take mine out as I have lots of wood mulch in place and would rather grow food in that spot in my permaculture garden https://www.gardenmyths.com/comfrey-dynamic-accumulator/
Thanks for the thought-provoking articles. The first article you reference is in relation to comfrey consumed internally, which I don’t recommend. It is perfectly acceptable to use as a topical healer, however. You can find its main ingredient, allantoin, in lots of over-the-counter personal care products such as lotion. I make an herbal salve from it.
The second article you reference is a good resource; the comments are even better. Comfrey may ultimately not be a nutrient accumulator. However, what we’re learning is that the benefit of herbs like comfrey is in their ability to produce epic amounts of biomass. This plant matter, which contains little cellulose, attracts and feeds soil organisms, which break it down quickly. This, in turn, makes nutrients more quickly bioavailable to plants than the NPK in chemical fertilizers.
Where there is more soil life, there is more bioavailability of administered nutrients. Maximize nutrient absorption rates by improving the microbial activity in the soil. To do that, feed them what they like to eat. They prefer organic matter over chemical fertilizer any day. In fact, some studies have even shown that chemical fertilizers kill soil organisms and mycorrhizal fungi.
Living soil is more resilient to pests, as well as temperature and weather extremes than dead, chemically-propped-up soil, so I continue to look for plants that are good producers of biomass, regardless of their nutrient claims.
I am involved in a project that is looking at stopping polluted water getting to rivers from farmyards.
We are planting Russian comfrey along the sides of open drains carrying the dirty water which then travels across a level patch of willows to reach the river.
The plan is to cut the comfrey 3 times each summer and feed it to the livestock. The willow will be harvested every 3 years for heating the farmhouse. If the nutrients are not cropped and removed from the system it becomes overloaded in a few years. So our hopes are pinned on comfrey.
Willow and comfrey are both excellent plants for this application, but would be more effective as part of a diversified buffer strip. Multifunctional riparian buffers present an incredible opportunity for increased biodiversity and harvests.