Comfrey

The permaculture fertility workhorse - a big bristly perennial with a six-foot taproot, cut three or four times a season for mulch and compost. Two things to know first: it is hepatotoxic and no longer used internally, and once established it is effectively permanent.

Plant sterile Bocking 14 root cuttings or crowns in a permanent spot - garden edge, orchard floor, dedicated bed - three feet apart in deep soil and full sun to part shade. It asks for nothing after the first season.

Comfrey is close to unkillable, so growing it is mostly a question of where. Give it full sun to part shade and deep soil that it can drive a taproot through; it will grow in clay, in poor ground, and in a surprising amount of shade, and it tolerates heat and drought once established. What it does not tolerate is ground that stands waterlogged all winter, which rots the crown.

Choose the plant carefully. Common comfrey (Symphytum officinale) sets viable seed and self-sows; the Russian hybrid S. × uplandicum selections known as Bocking 14 and Bocking 4 are effectively sterile, higher-yielding, and are what almost every experienced grower plants. Bocking 14 is the standard for cutting; Bocking 4 is the older livestock-forage selection. Either way you are buying root cuttings or crowns, not seed.

Plant two- to three-inch root pieces horizontally two to three inches deep, or crowns with the growing point just at the surface, spacing them three feet apart — a mature clump is a yard across. Three to five plants is plenty for a home garden; a dozen will mulch a small orchard. Water through the first summer while the root goes down, then essentially leave it alone. Do not put it in a rotation bed, a raised bed you might want back, or anywhere a rototiller will pass: site it at a garden edge, along a fence line, on an orchard floor, or in a dedicated bed ringed by mown grass.

Cut it hard and often - that is the entire regime. No feeding, no watering after year one, no staking. The only real management jobs are containing it and, on seed-setting types, cutting before seed drops.

An established comfrey plant needs no feeding, no watering and no staking. The care regime is simply to cut it: take the clump down to two or three inches above the crown whenever it reaches roughly knee height, which in most of the country means three or four cuts between late spring and early fall. Heavy cutting does not weaken it in the least — an uncut clump just gets coarse, leans over, and stops being useful. Stop cutting about six weeks before your first frost so the plant can rebuild its reserves.

Everything else is containment. Comfrey spreads two ways: by seed on the wild species, and by root wherever the ground is disturbed. If you are growing common comfrey rather than a Bocking cultivar, cut each flush as it finishes flowering so it cannot drop seed. And never dig, fork or till through a clump you want to keep in bounds — every severed fragment becomes another plant. A ring of regularly mown grass around the patch is the simplest effective barrier there is.

Wear gloves and long sleeves for cutting. The stiff hairs on the leaves and stems scratch and irritate forearms, and this is a plant whose sap you do not want near your mouth. Comfrey has almost no pest or disease problems worth naming apart from comfrey rust, which disfigures leaves in wet summers and is best handled by cutting the affected growth off and binning it rather than composting it.

Cut for the garden, never for the kitchen: chop-and-drop mulch around fruit and hungry crops, compost activator in layers, or a potassium-rich liquid feed steeped in a lidded barrel. Three or four cuts a season from a mature clump.

Everything cut from comfrey goes to the garden, never to the kitchen. There are three standard uses, and a mature clump supplies all of them.

Chop and drop. The simplest and best: cut the leaves and lay them thick, unshredded, around fruit trees, currants and gooseberries, potatoes, tomatoes, squash and anything else hungry. They wilt within a day and rot down within weeks, releasing a notably potassium-rich feed exactly where the roots are. Keep the material a hand's width clear of stems and trunks.

Compost activator. Comfrey leaves are high in nitrogen relative to their bulk and break down fast, so layering them through a heap of drier material gets it heating. A few armfuls will visibly restart a stalled compost pile.

Liquid feed. Pack cut leaves into a barrel or bucket, weight them down, add just enough water to cover, and put a lid on it — the resulting black concentrate after three or four weeks is excellent diluted about one part in ten for tomatoes, peppers and anything fruiting, and the smell is genuinely appalling. Site the barrel away from the house. Wear gloves throughout; nothing from this plant is drunk, eaten, brewed as tea, or fed to livestock.

Root cuttings, and they work almost too well - a two-inch piece of root buried two inches deep becomes a plant. That same ease is exactly why an established patch cannot be dug out.

Comfrey is propagated from root cuttings, and it is about as easy as propagation gets. Lift a section of root in early spring or fall, cut it into pieces two to three inches long, and bury them horizontally two to three inches deep in the new position. Almost every piece grows. Crown divisions — a spade-slice off the side of an established clump with a growing point attached — work just as reliably.

It is worth sitting with what that means. The same trait that makes comfrey trivial to multiply is precisely what makes it impossible to remove: any fragment of root left in the ground when you dig, fork or till becomes a new plant, and a rototiller run through a clump will plant a whole bed of it. This is not a plant you can move on a whim, and it is not one you can share out of a bed you are also trying to clear.

Seed is a different matter, and largely a warning rather than a method. Common comfrey sets viable seed and self-sows freely, which is how it turns up in hedge bottoms and along ditches across much of the country; the Bocking cultivars are effectively sterile, which is one of the main reasons to grow them. If you have a seed-setting plant, cut it before the seed ripens.

The historic 'knitbone' - genuinely rich in allantoin, and genuinely hepatotoxic. Internal use is no longer recommended by anyone credible and oral products are restricted in several countries; external use on unbroken skin remains traditional but is still debated.

This section records how people have traditionally used this plant, and what is known about the risks. It is history and general information — not medical advice, and not a recommendation to treat anything. Plants are not dosed like medicines, some interact with prescriptions, and some are harmful in ways that are not obvious. Talk to a clinician before using any plant medicinally.

Comfrey's folk name is knitbone, and for centuries the leaf and root were poulticed onto sprains, bruises and fractures and brewed as a tea for a long list of internal complaints. The plant is not inert: it is rich in allantoin, a compound that promotes cell proliferation, along with rosmarinic acid and mucilage, and topical comfrey preparations have been studied for sprains and joint pain with reasonably encouraging results.

That is where the good news ends. All parts of comfrey contain pyrrolizidine alkaloids, which the liver converts into compounds that damage the small hepatic veins. The result — hepatic veno-occlusive disease — is serious, can be fatal, and can develop after prolonged use rather than a single dose. The alkaloid load is far higher in the root than the leaf, and higher in young leaves than old, and Russian comfrey generally carries more than common comfrey. On the strength of this, the US FDA advised removal of oral comfrey products from the market in 2001, and several countries ban or restrict them outright.

The honest position for a garden page is therefore blunt. Do not take comfrey internally in any form — no tea, no capsules, no tincture, no root decoction — and do not give it to children or to animals as feed. External use on unbroken skin, for a limited period, is what commercial comfrey ointments still do and is the only application with meaningful modern support; even there, alkaloids are absorbed through skin, so it is avoided on broken skin, in pregnancy and while nursing, and is not for long-term daily use. Grow comfrey for your soil, not for your body.

A European medicinal herb carried to America by colonists, reinvented in the 1950s by Lawrence D. Hills as the Bocking fertility cultivars, and then removed from the internal-medicine repertoire by the pyrrolizidine research of the 1970s and 80s.

Comfrey has been a European medicinal plant since antiquity — the name traces back to Latin roots meaning to grow together, matching the folk name knitbone — and it travelled with colonists to North America as a standard dooryard herb, from where it escaped into ditches and hedge bottoms across the continent. The Russian hybrid S. × uplandicum arrived in Britain in the nineteenth century, promoted at first as a livestock forage crop.

Its modern identity was made in the 1950s by the English gardener Lawrence D. Hills, who trialled comfrey strains at Bocking, near Braintree in Essex, and selected the numbered clones — of which Bocking 14 became the standard — for yield, disease resistance and sterility. Hills founded the Henry Doubleday Research Association, named for the Victorian Quaker smallholder who had championed the plant, and it was through that organic-gardening movement that comfrey became the fertility staple of permaculture rather than a medicine.

The medical chapter closed in the decades that followed. Research through the 1970s and 1980s established the pyrrolizidine alkaloid content of the genus and linked comfrey preparations to hepatic veno-occlusive disease, and regulators moved against oral products — Canada, Germany, the UK and eventually the US FDA in 2001. What survives is a plant with an emphatically horticultural future: the same deep root, the same enormous leaf crop, entirely reassigned from the medicine cabinet to the compost heap.

The two questions that matter are how to get rid of it (slowly, by exhausting it) and whether a rosette is comfrey or foxglove (comfrey is bristly, foxglove is downy - if in doubt, discard it). Rust and slugs are the only real pests.

“Is this rosette comfrey or foxglove?” This is the one genuinely dangerous question on the page. Foxglove's first-year rosette closely resembles young comfrey, and people have died brewing it as tea. Comfrey leaves are coarsely bristly — noticeably rough and scratchy to the hand; foxglove leaves are soft and finely downy, with scalloped-toothed edges and a strongly netted pattern of veins underneath. If there is any doubt at all, discard the leaf. Better still, never plant foxglove anywhere near comfrey, and pull foxglove seedlings out of the comfrey patch on sight.

“How do I get rid of it?” Slowly, and by exhaustion rather than digging. Cut or mow every shoot off at ground level as soon as it appears, repeatedly, for a full season or two — you are starving the root, not removing it. Alternatively smother the ground with heavy cardboard and a thick mulch for a full year. Do not rototill, and do not settle for one thorough dig: both just distribute root fragments, each of which regrows.

Orange-brown pustules under the leaves: comfrey rust. It disfigures rather than kills. Cut the whole clump off at the crown, bin the foliage rather than composting it, and the regrowth usually comes back clean.

Ragged holes in the young leaves: slugs, on the softest spring growth. Rarely worth acting on — the plant outgrows them within weeks.

The clump flops open in the middle: it is overdue a cut. Take it down to a few inches and it regrows upright.

Seedlings appearing everywhere: you have seed-setting common comfrey rather than a Bocking cultivar. Cut each flush as it finishes flowering, and pull volunteers while they are small — once a seedling has made its own taproot it is a permanent resident.

The crown rotted over winter: winter wet, not cold. Replant on a slight rise or somewhere better drained.

Hardy and adaptable from zone 3 to zone 9 - it takes cold, heat, clay and drought once established. The main regional differences are how many cuts a season you get and whether it goes fully dormant in winter.

Comfrey is one of the more climate-indifferent plants in the catalog, growing well from roughly zone 3 through zone 9. Its deep taproot buys it real drought tolerance once established, and the crown is hardy well below zero.

Zones 3-5: reliably hardy; the crown dies back completely and reappears in mid-spring. A shorter season means two or three cuts rather than four. Plant in spring rather than fall so the root is down before the first winter, and mulch new crowns their first year.

Zones 6-8: the sweet spot — three or four cuts a season, vigorous regrowth, and no particular management beyond keeping up with it.

Zone 9 and the hot South: comfrey takes the heat but often slows or goes semi-dormant through the hottest part of summer, then flushes again in fall. Give it afternoon shade and it holds up better; expect the main cuts in spring and autumn rather than midsummer.

Arid West: it will grow with irrigation and repays a deep soak between cuts, but it is not a dryland plant in the sense of thriving unwatered in the desert. Everywhere, the limiting factor is not cold or heat but winter wet: ground that stays saturated all winter rots the crown, so plant on a rise if that describes your site.