How to grow Comfrey in Australia

Where to plant

Comfrey grows in sun or part shade in almost any soil, and grows biggest in rich, moist soil with some old manure. Choose its spot carefully: its deep roots make it very hard to move or remove, and any piece of root left behind will regrow. A corner of the garden, a spot near the compost heap, along a path or under fruit trees suits it well.

Common comfrey (Symphytum officinale) is naturalised in parts of Victoria and New South Wales and sparingly elsewhere, and Russian comfrey (Symphytum x uplandicum) has been recorded escaping in weedy sites near Melbourne. Grow the sterile variety Bocking 14, which does not set seed, and keep it away from bushland and waterways.

• Melbourne, Canberra and Hobart: fully hardy; it dies down in winter and regrows in spring. Plant in autumn or spring.
• Sydney, Adelaide, Perth, South East Queensland and the Northern Rivers: plant from autumn to late spring, and give it some afternoon shade and water through hot summers.
• North Queensland and Darwin: plant in the dry season; it grows best with some shade and regular water in the heat.

Choosing a variety

• Bocking 14, a selection of Russian comfrey (Symphytum x uplandicum), is the best choice for gardens. It is sterile, so it does not seed around, and it is high in nutrients. It is grown from root cuttings or crowns, not seed.
• Common comfrey (Symphytum officinale) grows from seed and can self-seed, so it is more likely to spread.

How to plant

1. Get a root cutting or small crown from a nursery or from a friend's Bocking 14 plant.
2. Plant root cuttings at least as long as your thumb horizontally, about 5 to 10 cm deep, or plant crowns with the growing points just at the surface.
3. Space plants about 60 cm apart, water in and keep moist until leaves appear.
4. In the first year, cut the leaves only once, in late spring, so the plant can build its roots.

Watering and feeding

Water young plants until they are established; after that comfrey needs little care, though it grows much more leaf with regular water in dry weather. It is a hungry plant and responds to a dressing of old manure or compost in spring.

Pruning and care through the year

• From the second year, cut whole plants back to about 5 cm above the ground every five or six weeks through the growing season. They regrow quickly.
• Stagger the cuts across a few plants so some are always flowering for the bees.
• Wear gloves and long sleeves when cutting; the bristly hairs on the leaves and stems can irritate skin.
• Do not dig or rotary hoe around comfrey, as every root fragment can grow into a new plant.

Using comfrey leaves in the garden

Liquid feed: pack cut leaves into a bucket or drum with water, about 1 kg of leaves to 15 litres, weigh them down and cover with a lid. After three to five weeks the liquid is dark and very smelly. Dilute it about one part to ten with water, to the colour of weak tea, and use it on fruiting plants such as tomatoes, capsicums, cucumbers and flowering plants. Use it fresh rather than storing it.

Concentrate: pack leaves tightly into a container with a drip hole and no water, and collect the dark liquid that drains out as they rot. Dilute it well before use.

Mulch: lay fresh or wilted leaves around fruit trees and hungry vegetables, or under a thin layer of soil or other mulch, where they break down quickly.

Compost: add cut leaves to the compost heap to speed it up.

Growing in pots

Comfrey can grow in a large, deep pot, at least 30 cm wide and deep, which also keeps it from spreading. Water regularly and feed it well, as a potted plant has less root room to draw on.

Safety

• Do not eat comfrey or drink comfrey tea. It contains pyrrolizidine alkaloids that cause serious liver damage, including veno-occlusive disease, and they have also been linked to lung damage and cancer in animal studies.
• In Australia, comfrey is a prohibited plant in the Food Standards Code, and comfrey preparations for human or animal use are prohibited under the Poisons Standard, except for preparations used on the skin. The TGA confirmed this in 2023.
• Do not feed comfrey to livestock or poultry as a regular food; ask a vet for advice.
• Comfrey liquid feed and mulch are for plants only.

Propagating

Bocking 14 is grown from root cuttings or by dividing crowns. Dig up a section of root in autumn, winter or early spring, cut it into pieces a few centimetres long, and plant them horizontally. Almost every piece grows.