More about Comfrey

Comfrey is never far from me – either physically or mentally. It is one of those neglected crops that every now and again have a very limited number of enthusiasts to promote their virtues, and yet they never become popular with many mainstream farmers. It is not a difficult crop to grow on a large scale, but it does need different management to most other farm crops grown for animal feed, and either needs to be fed fresh or mixed with some other crop for silage.

A few stalwarts carry on in a small way, but many growers neglect it after a while. Over the years I have seen sellers of root-sets and offsets, dried leaves and roots either cease business or show “out of stock” as a permanent notice and very few who continue. I am continually thinking of suitable mechanical methods of cutting and carting on a farm scale as livestock feed, but have not devised anything better than using a forage harvester that chops and loads directly into a wagon. This is suitable only for immediate feeding or ensiling. An alternative, when used as a mulch and fertiliser is to cut then pick up after wilting, although applying fresh cut leaves around trees in dry situations such as I have in the summer is my preferred use.

The best way to dry comfrey is to keep the leaves whole in a very shallow layer and turned frequently with great care to prevent shattering. Ideally they should be individually separated, but this is impossible except with only a few leaves. Bunched and hung up in a tobacco barn is feasible, but extremely labour intensive, and only suitable if you have a tobacco barn or something similar. I wilt in the field then use my numerous small olive harvesting boxes that have perforated bases and sides. Again, very labour intensive but the boxes are only used for olives in November and December when the comfrey is going into its dormant phase and not harvested.

The great problem for users of comfrey has often been that sellers and advisers do not know much about it, writing the most utter rubbish (often simply copied from other writings) about comfrey in general; Henry Doubleday and Lawrence Hills. I see the same misinformation time and time again, some even repeating articles that purport to be the writer’s own experiences of the crop. Sometimes sellers offer a specific cultivar, usually one of the Bocking series. I am always extremely suspicious of this in countries other than Britain, where Bocking 14 has been readily available for many years. Where did the plants originate? Who identified them?

I know comfrey is a wonderful plant, but I am sure it is not capable of making people into time travellers. I found one site referring to Doubleday in WWII - 40 years after he died, and here is an example from a site claiming to be a Herbal Encyclopaedia:

During the Irish potato famine of the 1840s, an Englishman named Henry Doubleday became convinced that the world could be saved from hunger and suffering by using comfrey. He established a charitable organization to research the cultivation and use of the plant that exists to this day and continues to publish pamphlets and books on its usage.

Henry Doubleday’s interest in comfrey was as a source of glue that could be used on postage stamps. He did not import what a century later became classified as Symphytum x uplandicum from Russia until about 1870. His earlier connection with potatoes was that he set up a factory in England to make starch from them. It was some years after his glue idea that he apparently saw the possibility of it as a source of human food, but it seems it remained only an idea. Unfortunately all his notes were destroyed after his death and it is not possible to know what his thoughts were. Lawrence Hills, in the 1950s, founded the research association to which he gave Doubleday’s name because of his work with comfrey.  For accurate historical information use Lawrence Hills’ works as your source, although it appears the botanic nomenclature was not settled when Hills wrote his books.

Many sites show photographs of a comfrey plant in its red or blue flowering phase and refer to it as S.officinale (Common Comfrey) when it is most obvious that it is not. They then claim that it does not set seed. Common Comfrey, as can be guessed from its name, sets seed profusely and will rapidly spread in a garden or field. Its flowers are white/cream/yellow. It is unlikely, but not impossible, that you will come across the red/purple flowered variant. Most other comfreys also set large amounts of viable seed. If you are growing comfrey to use either for animals or plants it should never be allowed to flower anyway. Flowering seriously reduces the productivity of the plant.  

Further misinformation arises when the writer has no idea about fertilisers. They confuse ratios of Nitrogen, Phosphorus and Potassium with percentages, comparing them as if they were the same thing and then spout forth about this being better than that, and how to make use of them. This is especially true of those promoting the use of comfrey. Part of the reason for this, although inexcusable by anyone who claims to advise on fertiliser use,  is the habit of some fertiliser sellers showing analyses of their products as, for example 5:10:10. The sign : between two numbers means that they are in this ratio to each other.  Agricultural and horticultural convention is 5-10-10 and also to show the constituents as N-P-K in that order, with other nutrients also shown as their elemental symbol, e.g S and Ca for Sulphur and Calcium.

For those who do not know, 5-10-10 means that the package contains 5% Total Nitrogen 10% Phosphate and 10% Potash. Nitrogen is the total of Nitrical and Ammoniacal; Phosphate is Phosphorus Pentoxide and Potash is Potassium Oxide. I suggest you read professionally written technical fertiliser articles if you require more detail about mineral or organic fertilisers and their availability to plants. A good starting point is the online available UK DEFRA manual RB209 “Fertiliser Recommendations for Agricultural and Horticultural Crops”. It is highly recommended to commercial growers, but only to those dedicated home growers with a thirst for knowledge.

The ratio of N:P:K in a 5-10-10 fertiliser is 1:2:2 but a ratio is meaningless if you want to know how much of that particular fertiliser to apply. You need the figures 5-10-10 or whatever the analysis is. Knowledgeable people can make use of the information and then make their own calculations based on the N-P-K percentages. Occasionally it will be found that some writers put Potassium in the middle. I have even seen this in agricultural books when the author discusses various fertilisers in the order Nitrogen, Potassium and Phosphorus. This is also inexcusable, and has given rise to some articles where I have seen the symbol for Potassium given as P and Phosphorus as K. Organic fertilisers (such as comfrey, meat and bone meal or seaweed) are described in the same way as mineral fertilisers so that users know their analysis and can make use of the information.

I use fresh and dried comfrey. I have made liquid from comfrey but found it did not suit my management systems. Liquid is obtained from the pressed leaves and stems. A favourite instruction is to dilute the liquid obtained from comfrey until it is “the colour of weak tea”. I have lost count of the number of times I have seen this quote. It is sometimes accompanied by “that is about 10:1” or 20:1 or 40:1. There is a big difference between 10:1 and 40:1. Even well-known gardening personalities come out with this nonsense. It is equally as bad as advising the use of a manufactured fertiliser by saying put “some” on your land. You have no idea what you are feeding your plants. The nutrients in a concentrated comfrey liquid are variable to begin with. The amounts in any given sample of fresh material will be different to another sample (more so if grown on a different site) and the moisture content, up to 90%, will also differ. Wilting the leaves is generally advised before pressing, but again how much water is left?

The agricultural college in Castelo Branco analyses comfrey leaves for me in the same way as they analyse olive and almond leaves to assist in assessing fertiliser requirements for the grove or orchard. It is unable to analyse the liquid and that is another reason I do not use it. It is possible to have a liquid analysed, but not locally. I would need to do some calculations based on the dried material of a wilted sample used for pressing in order to have an idea of the liquid analysis. Highly inaccurate, but the best I could do, and given the variability in starting water content of “wilted” leaves it is not good enough for me.

At the same time, if you grow comfrey on a garden or allotment scale, then making liquid concentrate may suit you rather than using the leaves fresh or drying them and a few years experience of using your own materials and methods should be enough that you know how to use it for your own crops. Analyses of leaves and liquid are very expensive (several times more than soil analyses) and possibly not justified for home use. I am on a bigger scale and using it for commercial crops. I am about to offer dried leaves for sale too, so I need to be able to calculate my own applications to plants, and to guide customers. Consequently I need the analyses.

I took samples from August and September cuts of the 2014 crop, did a thorough mixing, and had some analysed. These are the dried leaves I will be selling over the 2014-15 winter and spring. There will be a little variation in the analysis of a plant between the several cuts in a season and I will analyse more in 2015. It will take me a little while from posting this blog before the website is updated to include the comfrey. I will make an announcement here and also set up a dedicated blog that will give some suggestions on using the dried leaves – based on the latest analyses I have. I do not expect them to change to the extent that general advice needs to be changed, but it will be of interest to some amateur growers of comfrey to see if the analyses change.

What the present analyses have shown me is that I can provide all the P and K I need for my trees, and I expect (but do not know for certain) all the trace elements too, solely from comfrey. But not sufficient N. A large quantity of comfrey is required, and my original thoughts were to grow comfrey in the tree lines to make use of the fertilisers applied to the land and not utilised by the trees and also to eliminate carting of the cut comfrey used as mulch for the trees. Unfortunately despite my best endeavours to keep the tree lines clean, I am finding that birds are bringing in seeds and dropping them as they roost in the tree branches. I like to see the wide range of birds that inhabit my olive groves but blackberries and some of the bigger perennial and annual weeds are particularly troublesome.

I have reluctantly decided I would be unable to keep the olives, almonds and comfrey sufficiently weed free, and need to grow the comfrey on a dedicated area. If you have a few fruit trees, then you probably have the space for comfrey too. Think about growing a few comfrey plants close to each tree, specifically for the purpose of mulching the trees. 50kgs of fresh leaves is the minimum amount you will need for each medium sized productive tree.