Comfrey is rich in Potassium, and is a fantastic fertiliser for fruiting plants. ‘Bocking 14’ is a sterile cultivar of Russian Comfrey which is very high in nutrients and doesn’t self-seed.
There are 4 ways of using comfrey as a fertiliser (see Garden Organic for more detail).
Chop ‘n’ drop mulch: grow the comfrey near a fruit tree that has high nutrient demands, then a couple of times a year, chop it back and lay it on the ground as a mulch.
Comfrey feed: Stuff a bucket full of comfrey stalks & leaves, weigh down, cover with water. Leave for 4-6 weeks. Absolutely stinks, strain off liquid, put sludge on compost. No need to dilute before applying.
Concentrated comfrey feed: two containers, one with holes in bottom. Weigh comfrey down in container with holes, as it decomposes, thick brown liquid collected by other container. Not so stinky. Dilute 10:1 before applying.
Dry comfrey sprinkle: dry comfrey leaves in a hot, dry place (eg polytunnel). Skrunkle them up to dust, sprinkle them on base of plants. Acts as slow release fertiliser. Doesn’t smell at all. Note: this is experimental, not sure how well it works!!