Why should I grow comfrey and how do I use it? These are the two questions which any organic grower needs to answer.

comfrey flower Comfrey is a remarkable plant. It can be used to create a powerful liquid fertiliser, as well as a compost activator to produce enriched compost. It can create a fertiliser base within the soil, as well as a nutritious mulch on top. You can also use the dead leaves to make leaf mould as a nutritious potting compost.

Comfrey leaves contain the vital nutrients of nitrogen, phosphorus and potassium – all of which are needed by growing plants. These nutrients are released as the leaves decay. Potassium is used particularly to promote healthy flowers, seed and fruit: comfrey leaves contain up to three times more potassium than farmyard manure.

It is a member of the Borage and Forget-me-not family (Boraginaceae). Our researches have shown that ‘Bocking 14’, a cultivar of Russian comfrey, has a higher nutrient content than the common wild comfrey, and its leaves can be cut several times in a season. It also produces very few seeds for germination, and therefore it won’t dominate your growing area.

How do I grow comfrey?

Choose your site carefully – comfrey can live for 20 or more years. It is too vigorous to grow in a pot, but it will grow on most soil types (except the very shallow and chalky), thriving in good soil in the full sun. If you plant cuttings in spring you will be getting your first leaf harvest before the end of the growing season. Allow 60–90 cm between plants. Once established, it needs very little maintenance, however to maximise your comfrey crop, extra feeding with manure and compost or grass clippings will all help to produce more leaves. Remove flowering stems in the first season to gain maximum leaf growth next year.

How do I use comfrey?

Cut off the leaves about 5 cms above soil level. Wear gloves, as the stems are covered in stiff hairs that can irritate the skin. You can cut throughout the season, but not after September to allow a final autumn growth before winter. You can use the leaves in 3 different ways: as a liquid feed, as a compost activator or straight into or on the soil as a plant fertiliser.

How to make Comfrey tea

Adding the leaves to a container of water allows them to decompose into a highly nutritious liquid fertiliser. Fill a bucket or barrel with water and add approx 1kg of cut or bruised leaves to every 15 litres of water. You needn’t be too precise! Cover, and after 4-6 weeks a noxious (very) smelly brown liquid is ready for use. There is no need to dilute, and you can put the residue of leaves at the bottom onto the compost heap.

To make a concentrate, you don’t need water. Instead, packing the leaves tightly in a container, such as a lidded plastic bucket or a 2 litre drinks bottle, creates a black concentrated liquid which can be stored for up to a year. And it’s not quite so smelly!

You will need:

• 2 litre capacity plastic drinks bottle, without a cap
• collecting vessel – large yoghurt pot, ice cream carton or similar

Cut off the bottom of the bottle, pack in the comfrey leaves and stand the bottle upside down in a container. Cover the open end with a polythene bag, held in place with an elastic band, to prevent drying out. Comfrey liquid will drip out of the bottle into the collecting vessel. This concentrate should be watered down according to its strength – when thick and black, dilute 1 part feed to 20 parts water; when thin and brown, dilute 1 to 10. This needn’t be too precise!

Use as a summer feed for: tomatoes, peppers and cucumbers (apply as soon as the flowers have set fruit); for hanging baskets and pot plants; and for other hungry flowering plants such as clematis and dahlias.

Comfrey compost activator and leaf mould

Place cut or bruised comfrey leaves in alternate layers throughout your compost heap. Their decomposition will encourage bacterial action causing the heap to heat up and thus speeding up the composting process.

When leaves are added to a leaf heap, their nutrient-rich liquid absorbed within the mould, making it a perfect medium for growing seeds and potting compost.

As a trench fertiliser and as a mulch

Line the bottom of your potato and runner bean trenches with comfrey leaves and cover with a thin layer of soil. After planting your tubers or beans, fill the trench as usual, and the comfrey leaves will be broken down by the soil bacteria to provide a potassium-rich fertiliser.

Alternatively place a layer of leaves 5 cms deep on the surface of the soil around all plants. This will not only slowly rot down to provide nutrients, but also act as a mulch to help control weeds (especially with an extra topping of grass cuttings).