Herb · Boraginaceae
Comfrey
Symphytum officinale
A rugged, deep-rooted perennial that feeds your compost and refuses to quit once its roots take hold.
Full sun
Every 3–7 days
USDA 3–9
2–4 ft · 0.6–1.2 m
Overview
Comfrey is a stout, broad-leaved perennial from the borage family, prized by gardeners for its foliage far more than its form. Its leaves are large, hairy, and bristly to the touch, fed by a deep taproot that hauls nutrients up from soil layers most plants never reach, which is exactly why people harvest it for mulch and compost. Nodding, bell-shaped flowers in purple, pink, or cream hang from the stems and pull in bees from late spring into summer.
It demands almost nothing. The plant settles for full sun or partial shade, brushes off cold all the way down to -4°F (-20°C), and once that taproot is anchored it rides out dry spells that would wilt a thirstier neighbor. Hand it a moist, fertile patch and it climbs up fast and full-leaved.
The trade-off is permanence. Every fragment of root left in the soil can throw up a new plant, which makes comfrey almost impossible to remove once it is established. Choose its position with real care, because wherever you set it is most likely where it will remain.
Care
The short version: full sun to part shade in deep, rich, moist soil. Keep it watered while it is taking hold, feed it next to never, cut the leaves for mulch right through the season, and place it where you are happy to keep it for keeps.
Light
Comfrey thrives in full sun or partial shade. Full sun yields the fullest leaves and the freest airflow, which keeps the foliage fungi from settling in, while a touch of shade does no harm in hotter spots.
Water
It favors soil kept evenly moist and feels right at home in the damp ground beside ponds or ditches. Water it steadily while a young plant finds its feet. Once the deep taproot has dug in, an established clump rides out dry spells with little bother.
Soil
Set it into deep, fertile, moisture-holding loam with plenty of organic matter dug through. Comfrey is relaxed about pH and accepts anything from 6.0 to 7.5, but the richer and deeper the ground, the larger and quicker it grows.
Temperature
This is a truly hardy plant, at ease across -4°F to 86°F (-20°C to 30°C). It dies back through winter and sends up fresh growth in spring, unbothered by deep freezes.
Humidity
Average humidity of 40% to 70% suits it nicely, and it is not particular. Packed, motionless air is the one genuine hazard, since it invites the rust and mildew that mark up the leaves, so leave room for air to circulate.
Feeding
Comfrey hardly needs feeding at all. A light dressing of compost or aged manure in spring is more than enough, because this is a hungry accumulator that mines its own nutrients and ends up feeding other plants instead of asking to be fed.
Pruning
Shear the leaves back several times a season for mulch or compost, and the plant springs right back. Clip off the flower stalks if you would rather it not self-seed, and pull on gloves and long sleeves, because the bristly leaves can prickle and irritate the skin.
Repotting
Comfrey and containers are a poor pairing, all because of that deep taproot. If you do keep it in a pot, divide it every year or two, and keep an eye out for roots circling, slipping through the drainage holes, or soil that dries almost the moment you have watered it.
Size & spacing
A grown plant reaches 2 to 4 feet (60 to 120 cm) in height and fans out 24 to 35 inches (60 to 90 cm) across. Allow each clump that much space so air flows freely and the big leaves stay free of rust and mildew.
When to plant
Comfrey follows the seasons rather than fixed dates. Plant divisions or root cuttings in spring as soon as the soil is workable, watch the flowers unfurl from late spring through summer, and cut the leaves several times across the growing season for mulch and compost.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring, from root cuttings or divisions set into prepared, fertile soil
- Harvest: Nodding bell-shaped purple, pink, or cream flowers appear from late spring through summer; leaves can be cut several times a season for mulch or compost once plants are established
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Comfrey is hardy, so nearly all its troubles come down to either cosmetic leaf fungi or the plant pushing into ground you never meant it to take. Match what you spot below and act on it early, before a small patch turns into a fixed one.
Fresh shoots pushing up from snapped pieces of root
Even a fingernail-sized fragment of the brittle taproot will sprout into a whole new plant, so digging or tilling beside a settled clump simply scatters it further. Lift every length of that deep root you can reach, then keep shearing or smothering whatever returns until the buried reserves are spent. The truthful answer is to pick the spot with care before planting, because clearing it out later is a long fight.
Fix:
- Dig out as much of the deep taproot as possible
- Repeatedly cut or smother new shoots to exhaust root reserves
- Site comfrey carefully from the start, as eradication is difficult
Rust-brown blisters under the leaf, yellow blotching across the top
Those raised orange specks are comfrey rust, a fungus that grips the underside of the leaf and puffs out a cloud of spores the moment you brush against it. Shear every marked leaf down to ground level and put it in the bin, not the compost heap. The new foliage that pushes up afterward almost always comes back unblemished.
Fix:
- Cut affected foliage to the ground and dispose of it (do not compost)
- Improve air circulation by thinning crowded clumps
- Allow vigorous regrowth, which usually emerges healthy
A chalky white bloom dusting the broad leaves
Powdery mildew spreads its pale, floury film over the wide leaf blades by late summer, especially where a clump sits packed tight in damp, still air. Strip away the most heavily coated leaves, open the planting up so air can pass through, and shear the whole plant back hard. Clean new foliage rises again once the breeze can reach it.
Fix:
- Remove and dispose of heavily infected leaves
- Increase spacing and airflow around plants
- Cut the plant back to encourage fresh growth
Toxicity
Comfrey holds pyrrolizidine alkaloids, natural compounds that poison the liver. The hazard is not a fast stomach upset but slow, building damage from eating it, so this is a plant to handle and grow rather than to swallow or feed. Keep it clear of food and out of the everyday diet of pets and livestock, and leave its old folk reputation as a tonic firmly in the past.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
The coarse, bristly leaves and their bitter taste usually keep cats away on their own, which is your best safeguard. The threat is to the liver rather than a sudden reaction, because the pyrrolizidine alkaloids stack up damage with each repeated nibble, so steer a curious cat well clear of the foliage.
Dogs Caution
The rough, hairy leaf surface puts most dogs off, and they tend to walk past it. A dog that gnaws on it regardless swallows liver-damaging alkaloids, and the harm builds quietly rather than showing as a quick bout of vomiting, so don't let it turn into a habit.
Horses Caution
Horses tend to graze around the plant, yet ongoing grazing or comfrey baled into cured hay is where the real risk lies. The alkaloids scar the liver across weeks and months, and signs such as weight loss or dullness surface only once the damage is well advanced.
Rabbits Caution
People sometimes hand comfrey to rabbits as a green, but a small body picks up liver strain from even modest, repeated portions. Treat it as a green to keep off the menu rather than a regular forage.
Livestock Caution
Cattle, goats, and sheep will eat comfrey as forage, but a steady diet of it packs the liver with pyrrolizidine alkaloids. The injury accumulates without warning, so it has no place as a main feed.
Birds Caution
Poultry and other birds may take a peck at the leaves, and the same liver-toxic alkaloids reach them too. Keep comfrey out of the everyday ration and offer it, if ever, only as a rare and minor green.
People Caution
Comfrey carries a long folk reputation as a healing herb, yet it is no longer advised for eating or drinking. The pyrrolizidine alkaloids are hepatotoxic, and repeated internal use can leave serious, lasting liver damage, which is why its place is on the skin or in the compost rather than in a brewed cup.
Do NOT ingest comfrey. Its pyrrolizidine alkaloids are liver-damaging, especially with chronic internal use, and the US FDA has advised against oral comfrey supplements; internal use is discouraged and restricted. Use it only topically or as a garden amendment (mulch/compost), wear gloves and long sleeves when handling because the bristly leaves can irritate skin, and keep it out of food and feed.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Most comfrey you meet in a garden is one of a handful of named forms, picked either to rein in its spread or to give the foliage a bit more show.
Symphytum × uplandicum (Russian comfrey, incl. 'Bocking 14')
A sterile hybrid clone planted far and wide for fertilizer and compost, valued because it seldom sets seed and so holds its own spread back.
Symphytum officinale 'Variegatum'
An ornamental selection carrying cream-edged leaves, grown for the look of that pale margin rather than for sheer vigor.
How to propagate
Comfrey ranks among the simplest plants to multiply, largely because nearly any scrap of its root is eager to grow into a full plant of its own.
DivisionEasy
Early spring or autumn · 4 to 8 weeks for visible new growth, with full establishment over one season
Increase your comfrey by slicing the crown apart in early spring or autumn, or by lifting root cuttings, since just about any length of that brittle taproot will take root. Fresh shoots break the surface in 4 to 8 weeks and the plant beds in fully across a single season. The very eagerness that makes it so simple to propagate is the same trait that makes it hard to contain, so plant each division exactly where you mean it to live.
Myths
Comfrey tea is safe to drink because it is a natural herb.
Being natural buys it nothing here. The pyrrolizidine alkaloids in comfrey are hepatotoxic and can do serious harm to the liver, and the US FDA has warned against oral comfrey products. Keep it on the skin or in the compost, never in a cup.
Once you pull the plant out, comfrey is gone for good.
A single scrap of root left in the soil brings it straight back. That deep, brittle taproot resprouts with ease, so a clump you thought you had dug out can keep returning for years. Plant it only where you are glad to keep it.