By Colleen Withall

Many years ago Lawrence Hill wrote a book on Comfrey which led to a new appreciation of this herb. Long used medicinally and known colloquially as “Knitbone”, his research showed that it is an invaluable aid to soil fertility.

Hills recommends the Bocking 14 variety of Russian comfrey (available from the Organic Garden Catalogue, or begged from a fellow gardener) as it is sterile and produced from offsets, which can be planted at any time of the year except in the depths of winter. This variety is richer in nutrients, and spreads by root growth rather than seeds – a useful attribute if one is negligent about cutting it before the flowering stage! However if, as I have, you have inherited a vast bed of the ordinary kind, do not worry. It works just fine, although you may sometimes find the odd comfrey plant growing up in the middle of another bed. Roger Higginbottom, who holds an allotment in Derbyshire, says this should not be a problem if the hoe is used regularly to prevent the seedlings growing. Once they root, they go down so deeply into the soil that an established plant is extremely difficult to remove.

A comfrey bed will last about 20 years. It should be in a sunny position, and will benefit from a dressing of compost in winter, although mine seems to do well and thrives on neglect. Once established, you may cut it down to about five centimetres above the ground about three or four times a year.

How to use it

Comfrey is a rich source of minerals. Photo: Christine Mackay

On potatoes Comfrey has an almost perfect ratio of nitrogen, potash and phosphorous. In comparison with farmyard manure, Hills shows it has more nitrogen, twice as much potash, but less phosphorous. It is an ideal potato and tomato food. If using the trench method of potato planting, put a layer of wilted comfrey at the bottom of the trench and lay the potatoes on this. I also mulch in between the rows with comfrey and grass clippings and as the plants grow it can be used as a general mulch, applying approximately 5cm around plants. It will break down fairly quickly so it may be better mixed with a high carbon mulch, such as leaves or straw to suppress weeds.

As a soil conditioner Simply cut and wilt for 24 hours, and place on the soil, where it will quickly rot down. It can be chopped and dug in without robbing nitrogen because it is very low in carbon.

As compost activator Wilted comfrey is an excellent compost activator, due to the speed with which it breaks down. Used in the heap and helped by the addition of what Lawrence Hills calls “Household Activator” i.e. diluted urine, it should get any heap off to a flying start. On its own, it can do a really good job of heating up the heap as well.

For potting compost Equal quantities of leaf mould and comfrey rotted down are said to make an ideal potting mixture, thereby saving the use of peat. I have not personally tried this, nor do I know anyone who has, so comments from those who have would be welcome.

As a liquid feed This is, I suppose, the best known use of the herb. Comfrey liquid can be made in two ways. The first is to fill a barrel with cut leaves and fill it to the top with water. Cover the barrel and leave it for a couple of weeks or more. When you lift the lid you will be greeted by a poisonous stink. Dilute this with water in a ratio of approximately one to ten, water on your plants, particularly tomatoes, and watch them lap it up. A different and less smelly way is to fill a container with comfrey – pack it well down – and put a weight on the leaves. After several weeks it will be possible to drain a thick syrupy liquid from the bottom of the container. A tap would make this easier. This has very little smell, and diluted at approximately one to fifteen with water, is ideal for those places where the smell would be a problem. The late Kathleen Jannaway, of Movement for Compassionate Living advocated watering carrots regularly with comfrey liquid, saying that they often grew carrots weighing one pound each by this method, and the smell kept the carrot fly away.

A fitting tribute

Finally, in tribute to the work Lawrence Hills did on comfrey, Faber have re-issued his book Comfrey Past Present and Future at a price of £15. One for the Christmas list – or perhaps you could request it from your local library?

This article appeared in Growing Green International magazine Num 25 (Summer 2010), p30.