Wednesday, 19 January 2011

Comfrey tea

I have said in several of the previous posts that I use comfrey, sweet cicerly and  nettle teas to inoculate charcoal.  I also use them as liquid fertilizers. 

I have grown comfrey (Symphytum officinale) for about 30 years now.  It has a beautiful pink purple flower and large dark green leaves.  It can grow up to 1.5m tall and is rather a thug in the vegetable plot if you allow it to be.  I have five 25ft rows of it.
Comfrey bed 
My plants are not the sterile  Bocking 14 and they produce seeds prolifically.  They will spread.  Their roots are very thick and robust and you can use them to propagate new plants.  They are, indeed, very good ground cover plants because little will grow under them particularly if you grow them closely.  

Neat comfrey coming out of the butt.
This butt does not have a tap

Whenever I feel in the mood I cut down the comfrey and put it into a butt (a water barrel) with a tap at the bottom.  The comfrey rots down to a black liquid and that can be drained out of the barrel.  Some people cover the comfrey in water but it is unnecessary.  The liquid is relatively high in potash (Potassium) so it is good for fruit and flowers.  Its percentage NPK is 0.74:0.24:1.19 for the Bocking 14 comfrey
which compares very favorably with commercial tomato liquid fertilizers. 

However, it costs nothing!

What goes into the barrel stays in the barrel.  It will all rot down regardless of how tall the comfrey grows.  It does get coarser as it gets bigger and takes a little bit longer to break down in the barrel but it still forms the black liquid.  Now, you might think that the decaying comfrey would block up the tap at the bottom of the butt but it decomposes so quickly that it rarely if ever blocks the tap. 

I kept a large bottle of comfrey liquid for about 3 years and it still seemed to be alright. I keep my comfrey for about 6 months to a year in the butt but I keep topping it up as I crop the comfrey. It lasts over the winter as well. 

Nowadays I bury most of the allotment undiseased waste in the comfrey bed and let the comfrey recycle it for me. It gets a dose of manure or lawn mowings along the rows when I have nowhere else to store them.
The stinging nettle (Urtica dioica) and Sweet Cicerly (Myrrhis odorata) also make valuable liquid fertilizers.  Ref: “Ear to the Ground” by Ken Thompson.

Both worm tea and comfrey tea seem to make tomatoes grow.  I don’t know the NPK ratio for worm tea but I don’t think that it would be too different from comfrey tea.  

Comfrey does smell when it is rotting down and that is why I put it in a covered water butt.  I do not put water with it because that makes it smell even worse.  If you are constantly using it, like I am, then the smell does not seem to be so bad.  I use it on all the vegetables although things like beans and peas together with tomatoes and pumpkins seem to thrive on it.  

Hunts (see comment below) said that he found maggots in the dried comfrey liquid.  I reckon that these were rat tailed maggots. They are larvae of one of the hoverflies such as Eristalis tenax.  The larvae are one of the few that will live in very polluted water.  While some hoverfly larvae feed on aphids, Eristalis tenax larvae probably live off bacteria or other microorganisms living in the polluted water.  

So how to make comfrey tea that will not go ‘off’.  I think that Hunts’ went off because all the water in it evaporated away.  So,  run it into old orange squash bottles –the large ones with a handle at the top.  Screw on the top and this will prevent the adult hover flies from reaching the liquid.  I have kept comfrey liquid for some time like this.  You can then dilute it down however you want.  I dilute  it down like Tomorite plant food. 

Nowadays, I put the comfrey liquid into a lidded dustbin full of charcoal so that the marinating charcoal soaks the tea up and I can put it onto the soil in a more sustainable form.  I suggest, and there is very little evidence I can quote on this, that the comfrey liquid nutrients will not be leached out of the soil quite so readily in this form.  This is one of the main principles behind the development of a method of creating Terra preta type soils in England's temperate climate. 

As Mikey says in the comments below, the comfrey leaves can be put into the worm bin as in the photograph below.  
However, I would fill this little bin up several times over with the amount of comfrey leaves that I produce.  So the large bins are also brought into service.  In addition to comfrey leaves, I put most of my pernicious weeds in this worm bin.  Bindweed Convolvulus sepium  and horse tail Equisetum arvense ( arvense meaning of the field) are the two main weeds added to the bin.  Comfrey leaves or not, the bin produces copious amounts of black tea like liquid which get mixed with the comfrey liquid manure.  In the front of the worm bin is an area of nettles Urtica dioica  which is also added to the worm bin and the comfrey bins.  It is all grist to the mill.  


  1. Hey, Tony, just seen your blog!

    We have Comfrey on the allotment. as my friend Gerry suggested we could use some to water our tomatoes with I put some in an old bucket & half filled it with water. As Gerry told me it would smell foul I put it in a place that I wouldn't smell it from - then I forgot about it! A couple of months later I looked at it & almost all the water had evaporated & the foul smelling liquid left was full of 100s of maggots of some sort! It made me feel so bad I threw the contents away & didn't make any more, I just composted the leaves!

    So how do I make Comfrey tea that won't go off & how can I determine the amount of water to concentrate to make some "tea"?

  2. Hi Hunts
    I'll edit my blog to try to answer your questions.

  3. Simple solution which everyone seems to be ignoring is to just add the comfrey leaves (preferably shredded) to your worm bin and put an interior gravel filter on the worm bin, add a spigot, elevate it a foot or so and let the worms and their accompanying bacteria do the work. Less work, one container, no odor...what's the problem? I do this with mine and harvest up to 6 gallons per day of worm tea/leachate (whatever), pour it over my garden veggies leaves and all and have nothing but fantastic results. The worms are happy, the veggies are happy and the Comfrey, being the unselfish and giving creature it is, also seems to be very happy. This isn't rocket science, is it?

  4. Will the tea last longer in the refrigerator .. This is my first time to make it, And Will it do the same if I put it in a blender and added it to water then let it sit I here the smell's not bad that way

    1. Hi Teresa,
      The tea would probably last longer in the refrigerator but I would not put mine in the refrigerator. There is no need unless you want to keep it for years. Mine lasts for a year in an old plastic dustbin at the back of my shed. I use it constantly. At the moment I am using it to water in the green manure seeds and the new grafted apple tree plants. I see no problem with using a blender. The nutrients will still be in the liquid regardless what processing you use. I just bung the leaves into a large water butt and leave them until a thick black liquid comes out of the bottom of the butt.
      Hope that your comfrey produces as good results as mine does.
      All the best,

  5. We have two big butts of the stuff on the allotment. They were there when we took over three years ago and we have just been topping up since. So what we are drawing off must be at least 3 years old. It stinks to high heaven but the plants seem to like it. It's certainly not doing any harm anyway.