Comfrey Tea - How to make your own liquid fertilizer

Comfrey is an essential plant to have in the vegetable garden if you have room. It needs to be controlled or it will spread everywhere. I was given a small piece of root (Russian Comfrey) by a friend a few years back which I planted out in autumn about 10-15 cm deep and just waited; the following year I was using the leaves as compost accelerator and making comfrey tea liquid fertilizer. This was my plant in the middle of May 2020.

It is an attractive plant producing lots of pinkish flowers that the bees absolutely adore. It is also a great source of NPK nutrients with levels not dissimilar to commercial tomato feed when made into comfrey tea (see below). For other useful facts and information on growing and using comfrey, see https://www.allotment-garden.org/comfrey/growing-using-comfrey-for-gardeners/. 

Be warned that comfrey tea smells and I wouldn’t describe it as a pleasant smell. Nettles can be used in place of comfrey for your ‘tea’ and I’m told the brew does not smell as bad; you could, of course, use a mix of both plants. However, I do not have space for a nettle patch sufficiently large for this purpose. If you have room for a nettle patch then go for it - many common garden butterflies (e.g. small tortoiseshell, red admiral, comma) lay their eggs on stinging nettles.

How I make comfrey tea

The basic principle is to soak comfrey leaves/stalks/flowers in water for a minimum of two weeks. You can make a ‘ready-to-use’ (i.e. already diluted) version in a water butt; see link above. However, because of space restrictions, I make a concentrate for dilution later. To do this fill a container full of chopped leaves/stalks/flowers, cover with water, add a weight to keep the plant material submerged and leave in a quiet corner. Always use a container with a tight-fitting lid as this avoids the odour annoying the neighbours.

I use an old Bokashi composting bin which comes with all the necessary features: a tap for drawing off the compost tea, a course filter to prevent leaves blocking the tap and a close fitting lid.

Using scissors, trim the comfrey plant and roughly chop into the bin until full - leave some flowers on the plant for the bees. Place a weight on top (I use an old roof slate recovered from the kitchen garden excavation), fill with water to the level of the weight and put the lid on. Leave for a minimum of 2 weeks. Dilute as you would any commercial tomato feed; typically 100 to 200 to 1 dilution.

You might want to use another plant food for indoors as the odour does not present a welcoming atmosphere. But for the garden, you do not need to buy plant food. Use this brew with homemade compost and biochar (more on these later) to maintain the fertility of your garden.