Comfrey has a deep taproot and an extensive root system that pulls nutrients from the soil and subsoil, where most other plants cannot reach. Comfrey is high in nitrogen, phosphorus and potassium and accumulates essential trace elements. It is therefore an excellent fertiliser for the garden.
The leaves can be used as a mulch around the base of plants or added to your compost heap. The leaves can also be rotted down into a liquid fertiliser.
Many different techniques for extracting the liquid are described on the web but, whichever one you choose, under no circumstances soak the leaves in water or add them to your water butt. I am told that you end up with something that stinks like a sewer!
The rim of the flower pot sits on top of the plastic inner lining of the bin. This leaves several inches free at the bottom of the bin for the comfrey juice as it drips through the holes in the pot.
I weight down the comfrey leaves in the flower pot with a couple of large stones in a plastic food tray. Then I cover it all with the pedal bin lid.
I dilute the comfrey juice about 15:1 with water and use it every couple of weeks, mostly on the tomatoes and chillies that are in pots.