There has been much written about the humble Comfrey plant with differing opinions. Some see it as a rampant weed others as a decorative addition to the flower border. For the organic gardener it is the most valuable non-food plant available and one that everybody should grow.

There are many ways to use comfrey; as a mulch, compost accelerator, as a high nutrient compost ingredient or as liquid plant food. More on this later but before we get down to practicalities it might be useful to know something of the history of how Comfrey came to be recognised as a star of the organic garden.

In 1954 Lawrence Hills, the founder of HDRA now Garden Organic, began researching the use of Comfrey. He found that because it ‘mines’ nutrients using its deep root system, the plant is very rich in the basic N-P-K (Nitrogen, Potash, Phosphorous) elements which are the basis of all fertilisers essential for plant health and vigour. Comfrey no doubt contains useful amounts of trace elements but nobody seems to have researched this.

Hills went on to develop the most useful variety of Comfrey, Bocking 14, which was named after the location of the trial grounds in Essex. The most important property of Bocking 14 is that it is sterile. That means it does not self-seed so does not spread like wild Comfrey. Having said that once you have Comfrey in the garden you will never get rid of it as even the smallest fragment of root seems to grow vigorously.

In his book “Comfrey, Past Present and Future” Hills listed the results of analysis of Comfrey grown at Bocking.

Comparative Nutritional Analysis of comfrey, compost and manure

Material Water % N% P % K % C:N
Farm Yard Manure 76.0 0.64 0.23 0.32 14:1
Wilted Russian Comfrey 75.0 0.74 0.24 1.19 9.8:1
Indoor Compost 76.0 0.50 0.27 0.81 10:1

He also made Comfrey juice by using 14lbs of comfrey leaves in a 20 gallon drum. Again the results of the analysis are shown below.

Material DM N P K
Tomorite 0.1410 0.0130 0.0139 0.0093
Comfrey 0.4090 0.0140 0.0340 0.0059

DM – dry matter, N – Nitrogen, P – Potash, K – Phosphorous

This shows that Comfrey is a very useful and valuable plant to have in the garden. By pressing the leaves and thin stems, and waiting for the dark brown juice to appear, it is possible to make a fertiliser as good as the best commercial brands. Not only is this a free source of nutrients for the garden it also fulfils one of the basics of organic gardening, sustainability, by creating a closed system.

Want to see how to make liquid fertiliser? Click here for more details.

Updated 13 May 2020