How to grow comfrey
Overview
Comfrey is a fast-growing, deep-rooted herbaceous perennial in the Boraginaceae family, grown for its large hairy leaves and nutrient-rich biomass. It is a dynamic accumulator that mines minerals from deep in the soil, making it invaluable as a mulch plant and compost accelerator in organic gardens.
Varieties
- Symphytum officinale 'Bocking 14' — A sterile, non-seeding cultivar bred for high leaf yield and low seed spread, ideal for Australian gardens.
- Symphytum officinale 'Bocking 4' — A Russian comfrey hybrid with higher nutrient content, often used for liquid fertiliser production.
Soil Preparation
Comfrey prefers a deep, fertile loam with pH 6.0–7.0. Before planting, dig in well-rotted manure or compost to 30 cm depth. Ensure soil is free-draining; heavy clay can be improved with gypsum and organic matter. Avoid waterlogged sites.
Growing Guide
Plant comfrey in full sun to partial shade in well-drained, fertile soil. Space crowns or root cuttings 60–90 cm apart, as established plants form large clumps. Set crowns 2–5 cm deep with the growing point just above soil level. For best leaf production, cut plants back to 10–15 cm high 2–3 times per year, and do not let them flower if you want maximum leaf harvest.
Care
Feed comfrey with a balanced organic fertiliser (e.g., 5-5-5) in early spring and after each heavy harvest. Cut back flower stalks before they set seed to encourage leaf growth and prevent self-seeding. Divide clumps every 3–4 years in autumn to maintain vigour and replant divisions at the same depth.
Companion Planting
Grow comfrey under the drip line of fruit trees such as apple, pear, and citrus to supply nutrients and suppress weeds. Avoid planting near shallow-rooted vegetables like lettuce or beans, as comfrey's deep roots can compete for water and space. It also pairs well with perennial herbs like fennel and yarrow.
Common Pests & Risks
Comfrey is generally pest-free, but snails and slugs may damage young leaves in wet weather. Control with beer traps, copper tape, or hand-picking at dusk. In humid areas, watch for powdery mildew on crowded plants; improve air circulation by spacing clumps.
Harvesting
Harvest comfrey leaves when they are 30–60 cm long and before flowers appear, cutting stems at ground level. Use fresh leaves as a green mulch or add to compost piles as an activator. For best nutrient content, harvest in the morning after dew has dried.
Troubleshooting
Yellowing leaves: often caused by nitrogen deficiency or waterlogging; feed with blood and bone or improve drainage. Brown leaf edges: indicates potassium deficiency or salt burn; apply wood ash or liquid seaweed. Stunted growth: likely due to compacted soil or root competition; dig in compost and loosen soil. Powdery mildew: white coating on leaves in humid weather; thin clumps and spray with milk solution (1:9).