Herb · Boraginaceae
Comfrey
Symphytum officinale
A tough, deep-rooted perennial that feeds your compost and never quits once it takes hold.
Full sun
Every 3–7 days
USDA 3–9
2–4 ft · 0.6–1.2 m
Overview
Comfrey is a big, hairy-leaved perennial from the borage family that gardeners grow for its leaves rather than its looks. It sinks a deep taproot that pulls nutrients up from well below the reach of most plants, which is why so many people cut it for mulch and compost. The nodding bell-shaped flowers in purple, pink, or cream draw bees from late spring into summer.
It asks for very little. Comfrey takes full sun or partial shade, shrugs off cold down to -4°F (-20°C), and once that taproot is down it handles dry spells that would flatten a thirstier plant. Give it a damp, rich spot and it grows fast and lush.
The catch is that comfrey settles in for the long haul. Every scrap of root left in the ground can sprout a new plant, so it is almost impossible to remove once established. Pick its place carefully, because where you plant it is most likely where it stays.
Care
The short version: full sun to part shade in deep, rich, moist soil. Water while it is getting going, feed it almost never, cut the leaves for mulch through the season, and site it where you are content to keep it for good.
Light
Comfrey grows happily in full sun or partial shade. Full sun gives you the lushest leaves and the best airflow, which keeps the foliage fungi at bay, while a little shade is fine in hotter spots.
Water
It likes soil that stays evenly moist and is at home in damp ground near ponds or ditches. Water steadily while a young plant is settling in. Once that deep taproot is down, an established clump handles dry spells without much fuss.
Soil
Plant in deep, fertile, moisture-holding loam with plenty of organic matter worked in. Comfrey is easygoing about pH and takes anything from 6.0 to 7.5, but the richer and deeper the ground, the bigger and faster it grows.
Temperature
This is a genuinely hardy plant, comfortable across -4°F to 86°F (-20°C to 30°C). It dies back in winter and pushes up fresh in spring, untroubled by hard freezes.
Humidity
Average humidity of 40% to 70% suits it well, and it isn't fussy. Crowded, still air is the only real risk, since it invites the rust and mildew that spot the leaves, so leave room for air to move.
Feeding
Comfrey barely needs feeding. A light dressing of compost or aged manure in spring is plenty, since this is a hungry accumulator that mines its own nutrients and ends up feeding other plants rather than needing to be fed.
Pruning
Cut the leaves back several times a season for mulch or compost, and the plant bounces straight back. Snip off the flower stalks if you'd rather it didn't self-seed, and wear gloves and long sleeves, because the bristly leaves can prickle and irritate skin.
Repotting
Comfrey and containers don't really mix, thanks to that deep taproot. If you do grow it in a pot, divide it every year or two, and watch for roots circling, escaping the drainage holes, or soil that dries out almost as fast as you wet it.
Size & spacing
A mature plant stands 2 to 4 feet (60 to 120 cm) tall and spreads 24 to 35 inches (60 to 90 cm) wide. Give each clump that much room so air moves freely and the big leaves stay clear of rust and mildew.
When to plant
Comfrey runs on the seasons, not a calendar. Set out divisions or root cuttings in spring once the soil can be worked, watch the flowers open 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 tough, so most of its problems are either cosmetic leaf fungi or the plant simply spreading where you didn't want it. Match what you see below and deal with it early, before a small patch becomes a permanent one.
New plants springing up from broken root pieces
Comfrey resprouts from the smallest scrap of its brittle taproot, so digging or tilling near an established clump only multiplies it. Lift as much of the deep root as you can, then keep cutting back or smothering anything that returns until the reserves run out. The honest fix is to choose the spot carefully before you plant, because eradication is hard.
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
Orange pustules under the leaves with yellowing on top
This is comfrey rust, a fungus that settles on the leaf undersides and releases its spores when you rub them. Cut the affected foliage right to the ground and bin it rather than composting it. The fresh growth that follows usually comes back clean.
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 dusty white film coating the big leaves
Powdery mildew turns up on the broad leaves in late summer, especially when plants sit crowded in humid air. Pull off the worst leaves, give the clump more room to breathe, and cut the plant back hard. New leaves push up clean once the air moves freely again.
Fix:
- Remove and dispose of heavily infected leaves
- Increase spacing and airflow around plants
- Cut the plant back to encourage fresh growth
Toxicity
Comfrey carries pyrrolizidine alkaloids, natural compounds that are toxic to the liver. The danger is not a quick stomach upset but slow, cumulative damage from eating it, so this is a plant to handle and grow rather than to eat or feed. Keep it out of food and out of the regular diet of pets and livestock, and let its long folk reputation as a tonic stay in the past.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
Cats usually leave the bristly, bitter leaves alone, which is the best protection. The worry is the liver rather than a quick reaction, since the pyrrolizidine alkaloids build up damage over repeated nibbling, so keep a curious cat away from the foliage.
Dogs Caution
Most dogs find the coarse, hairy leaves off-putting and steer clear. A dog that chews them anyway takes in liver-damaging alkaloids, and the harm shows up slowly rather than as an obvious upset stomach, so don't let it become a habit.
Horses Caution
Horses generally graze around comfrey, but steady grazing or comfrey in cured hay is the real danger. The alkaloids scar the liver over weeks and months, and signs like weight loss or dullness only appear once damage is well underway.
Rabbits Caution
Comfrey is sometimes offered to rabbits as a green, yet a small body takes on liver strain from even modest, repeated feeding. Treat it as something to avoid rather than a routine forage.
Livestock Caution
Cattle, goats, and sheep can take comfrey as forage, but feeding it regularly loads the liver with pyrrolizidine alkaloids. The damage is cumulative and quiet, so it should not stand in as a main feed.
Birds Caution
Poultry and other birds may peck at the leaves, and the same liver-toxic alkaloids apply to them. Keep comfrey out of the regular ration and offer only as an occasional, minor green if at all.
People Caution
Comfrey has a long folk history as a healing herb, but it is no longer recommended for eating or drinking. The pyrrolizidine alkaloids are hepatotoxic, and repeated internal use can cause serious, lasting liver damage, which is why it belongs on the skin or in the compost rather than in a tea.
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 in gardens is one of a couple of named forms, chosen either to slow its spread or to dress up the foliage.
Symphytum × uplandicum (Russian comfrey, incl. 'Bocking 14')
A sterile hybrid clone grown widely as a fertilizer and compost plant because it rarely sets seed, which keeps its spread in check.
Symphytum officinale 'Variegatum'
An ornamental form with cream-edged leaves, grown for its looks rather than for raw vigor.
How to propagate
Comfrey is one of the easiest plants to multiply, mostly because nearly any piece of its root wants to grow into a whole new plant.
DivisionEasy
Early spring or autumn · 4 to 8 weeks for visible new growth, with full establishment over one season
Multiply comfrey by splitting the crown in early spring or autumn, or by taking root cuttings, since almost any piece of the brittle taproot will grow. New shoots show in 4 to 8 weeks and the plant settles in fully over a single season. The same eagerness that makes it so easy to propagate is exactly what makes it hard to confine, so set each division where you want it to stay.
Myths
Comfrey tea is safe to drink because it is a natural herb.
Natural does not mean harmless here. Comfrey's pyrrolizidine alkaloids are hepatotoxic and can cause serious liver damage, and the US FDA has advised 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.
It comes back from the smallest scrap of root left behind. The deep, brittle taproot resprouts readily, so a clump you tried to remove can return for years. Plant it only where you are happy to keep it.