Composting · Herb · How to Grow · Profile · Soil care

Comfrey: How To Grow – Herb of the Month

Comfrey stats/requirements at a glance

Ease of Raising:
3/5 – Bi-weekly check-ups
2/5 – Minimal, twice per week (especially, container)
4/5 – Full sun, shade tolerant
1/5 – Minimal (harvesting keeps plant in shape)
1/5 – Minimal, at least during the growing season
Time to Harvest:
1/5 – Immediate (seedling) to Soon (from seed)
Frost Hardiness:
3/4 – Tender (can’t take mild frost)
Medicinal, Pollinator attractor & Compost
Most Problematic Nemesis:
Some caterpillar feeding
Container Plant:
Yes definitely
Comfrey Symphytum officinale Flora of Germany, Austria and Switzerland (1885) Kurt Stober Online Library
Comfrey, Symphytum officinale, Flora of Germany, Austria and Switzerland (1885), Kurt Stober Online Library

Quick intro

Comfrey is known for its healing properties and is currently also used as compost addition or as a liquid fertiliser, which is prepared from the leaves. Even though it has wonderful medicinal and composting properties, the plant may be considered as a weed by many.

Comfrey is native to Europe, especially Ireland and Britain, and temperate parts of Asia. It has been cultivated since 400BC due to its unrivalled potential for healing external wounds and broken bones, hence receiving its namesake ‘Knitbone’ or ‘Boneset’.
Comfrey was favoured amongst the Greek physicians, especially during times of war. Today comfrey is also grown in North America and it roots and leaves are still used for medicinal purposes.

Science Stuff

Comfrey belongs to the Boraginaceae family of herbs, the Forget-me-not family. This family mainly contains herbs with hairy leaves, including Borage, Fiddelenck, Forget-me-not, Alkanet, Lungwort and Bugloss.

There are two main species, wild or common comfrey (Symphytum offinale) and rough or prickly comfrey (Symphytum asperum). A hybrid variety exists as well between S. offinale and S. asperum, known as Russian comfrey (Symphytum x uplandicum).

Comfrey is used both internally and externally, but it is unadvised to use internally, as comfrey contains the toxin symphytine (Pyrrolzidine alkaloid), which causes liver damage and may be carcinogenic.

Comfrey leaves and roots are used to make extracts for extrernal use. These extracts contain allantoin, which stimulates the growth of new cells, rosemarinic acid, which is an anti-inflammaroty and mucilage, which soothes inflamed tissues. Roots contain twice the amount of allantoin than leaves. Comfrey is generally used as a cream and applied to affected areas that includes wounds, broken bones and is frequently used as a skin product.

Comfrey plant (Symphytum uplandicum)

Growing Comfrey

Leaves are main part of the comfrey plant used in the vegetable garden. Therefore it requires a fair amount of nitrogen to encourage good leaf production and will do well when fertilized with nitrogen-based mulch, such as animal manure or lawn cuttings.

Comfrey is difficult to grow from seed, as germination takes long (20 weeks) and is erratic. New plants can be successfully propagated from root cuttings. It is also advisable to grow comfrey in a container as it has a deep root system, making the plant nearly impossible to remove from the garden as new plants regrow from any root stumps left in the soil. Keep comfrey well-watered during the growing season if you plan to harvest leaves from it.

Comfrey plant (Symphytum uplandicum)

Essentially no pruning is required, since regular harvesting keeps the monster in shape 😉 .
Other Tips
Comfrey, specifically Russian comfrey, as a compost addition or liquid fertiliser is highly recommended when you have a vegetable patch. It is high in nitrogen (hence proteins), phosphorus and potassium (Good NPK values 🙂 ). For detailed NPK quantities of comfrey refer to Composting. If your comfrey is in the garden (and you tend to keep it there) then your comfrey will tap into deep nutrient reserves in the soil that can be recovered in the leaves.

Here are a few ways comfrey is used as a compost/feed addition:

✓ Compost activator – add to compost composed mainly of dry brown material. Layers of comfrey between the brown matter will heat the compost heap and assist with decomposition. Do not add too much comfrey as the comfrey will break down instead of assisting the decomposition of the heap.
✓ Comfrey mulch – a 5cm layer (2 inches) of fresh leaves around the stems of plant will break down slowly and release nutrient to the soil without removing nitrogen whilst decomposing (such as straw and leaves). It is good for just about any vegetable or fruit, but can be useful addition to nutrient guzzlers such as fruiting plants (tomatoes & fruit trees) and root vegetables (potatoes).
✓ Liquid feed – There are two ways to make liquid comfrey feed or comfrey tea. One is really smelly (the reason why I switched to the other) and the other is not.
o      Smelly: Simply cut the leaves into small pieces and add to a bottle or bucket of water and seal. After about 1-3 months, depending on the amount of leaves, you will have nasty smelling liquid feed. It works wonders, but the smell is terrible. It smells bad due to the anaerobic (no oxygen) decomposition of the comfrey in the water. Dilute this in a ratio of 1:10, 1 part of comfrey liquid to 10 parts water.
o      Not smelly: Place comfrey leaves in a plastic container with holes in the base. Weigh it down with a stone or brick. Place this container (with holes) in a second container. The second container can be lined with a plastic bag if you intend to re-use it for another purpose. Place a lid on this to prevent flies from making a breeding ground in there. As the comfrey decomposes it produces an odourless black syrup that drips to the bottom container. (Alternatively you can use one bucket with a hole and the comfrey placed on top of another. Comfrey will then drip into the bottom bucket for collection.) The comfrey liquid is a concentrate and therefore requires dilution before use. It is also diluted in a 1:10 ratio (1 part liquid comfrey to 10 parts water).
Liquid comfrey can be used on tomatoes or similar crops three times a week and potted plants once a week. The tea can be stored in glass jars in a cool dark place until further use.

If you have caterpillar feeding on your comfrey it is easiest to physically remove them from the plant. Other problems may include rust and powdery mildew. To control these, cut the plant to the ground and burn the infected leaves. New uninfected leaves should regrow rapidly.

Harvesting & Storing
Comfrey leaves can be harvested up to 5 times a year during the spring to summer months. Leaves are harvested once they are 30-60cm high (~ 1-2 feet).
Comfrey leaves can be dried, but they are brittle. Thus it is preferable to use comfrey leaves when they are fresh.
Seed Saving & Propagation
Russian comfrey (S. x uplandicum) produces clusters of pink, purple or blue flowers in summer. Common comfrey (S. officinale) produces white or pink flowers and is likely insect pollinated.

Comfrey plant (Symphytum uplandicum) flowers purple russian

Russian comfrey is preferred in the garden as it is sterile and does not self-seed yet bares the same nutrient-rich foliage properties of S. officinale.
Since comfrey is difficult to raise from seeds, root cuttings are used.
My Comfrey

I have the Russian comfrey. Originally one comfrey, which self-propagated from a leaf cutting if I remember correctly 🙂 . Very prickly, wear gloves if your skin gets irritated when you handle the leaves.

Comfrey flowers Russian (Symphytum uplandicum)



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