Comfrey as an Organic Fertiliser

The Fertiliser Plant

Comfrey (Symphytum × uplandicum, variety 'Bocking 14') is arguably the most useful plant in the organic garden. Its deep taproot — reaching down 1.5–2 metres — draws up mineral nutrients from subsoil layers beyond the reach of most plants. The leaves accumulate potassium, nitrogen, phosphorus, and trace minerals in extraordinary concentrations. Cut and composted or steeped in water, they provide a fertiliser that rivals any commercial product.

Bocking 14

'Bocking 14' is the variety to grow. It was selected in Bocking, Essex, by the Henry Doubleday Research Association (now Garden Organic) specifically for its high potassium content and, crucially, because it does not set viable seed. Common comfrey self-seeds prolifically and can become invasive. Bocking 14 spreads only by root, which is easily controlled.

Plant divisions (small pieces of root) in spring or autumn. Comfrey establishes quickly and will produce several cuts of leaf per season. It tolerates partial shade and grows well on the edges of the compost area, where cut leaves can be dropped directly in.

Making Comfrey Liquid Feed

The simplest method:

1. Pack a bucket loosely with comfrey leaves.
2. Weigh them down with a brick.
3. Cover with water and leave for 4–6 weeks.
4. The resulting liquid will be dark, foul-smelling, and extraordinarily potent.
5. Dilute 1:10 with water before applying to plants.

Alternatively, pack leaves into a sealed container with a tap at the base and no water — the leaves will slowly liquify under their own weight, producing a concentrated "comfrey concentrate" that is diluted 1:40.

Applications

The high potassium content of comfrey feed makes it particularly valuable for fruiting crops:

• Tomatoes (apply weekly once flowering begins)
• Cucumbers, courgettes, squash
• Peppers and aubergines
• Strawberries

Comfrey leaves can also be used as a mulch around potatoes, as a compost activator, or as a "chop and drop" mulch around fruit trees. Dried comfrey leaves make an excellent seed compost additive.

Dynamic Accumulator

Comfrey is the best-known "dynamic accumulator" — a plant that mines subsoil minerals and makes them available at the surface. Other useful accumulators include borage (silica), yarrow (potassium, copper), and nettles (nitrogen, iron). A patch of stinging nettles is a genuine asset to the organic garden — nettle tea provides a nitrogen-rich feed comparable to dilute blood meal.