One of my long term projects/goals is to make my garden more sustainable. One of the ways I'm slowly working on at the moment is to produce all my fertiliser requirements on site, supplemented by seaweed and manure foraging.
I planted some comfrey a couple of years ago around some of my fruit trees a la kay baxter. Given that it is planted into nearly pure clay the comfrey took a while to get going, but now is producing a decent crop of leaves. I've cut it back a couple of times to make some comfrey 'tea'. It's supposed to be incredibly high in nutrients, especially potassium, and a perfect tomato fertiliser.
Without fail the books etc say that if you are making comfrey liquid fertiliser to beware of the smell, which is awful. It has put me off making it for a while, as I've set up my place for making fertilisers right next to my 'on show' vege garden, so that it is convenient. But although I don't mind smells when I know that it is going to be good for the garden, I didn't think others would appreciate it so much. However I came across a few references that advised just putting comfrey leaves in a container to rot, and NOT to add any water. This way it wouldn't smell. So somewhat sceptically I stuffed a 20 litre bucket full of comfrey, put a lid on it, and then put it under the potting bench. A few weeks later I remembered it, opened it up, and look!
Super strong comfrey tea with no smell at all. I strained the liquid out, diluted with water in a watering can, and gave it all to the tomatoes. The remaining solid rotted down comfrey I tucked under the straw mulch next to the toms. I hope they appreciate it.
Buoyed up by success I have given the comfrey another haircut, and filled up two more buckets. On my 2011 list is to divide up the comfrey and plant around a few more trees. I don't know if it is possible to have too much comfrey for a garden my size.