Traditionally potatoes are of course earthed up as they grow. But as I have experimented here with no dig gardening techniques, I have moved to a system where I mulch around the growing potato plants rather than mounding up the soil around them.
I have tried various different organic mulch materials and while my experiments are by no means scientific, I have found that certain organic materials work better than others.
I have had great results mulching around the potato plants with a thick layer of comfrey leaves and that is what I have chosen to do this year. This mulch breaks down quickly, and the comfrey is growing so quickly that there is a bounty of material to use.
The comfrey leaves are good for retaining moisture during a time of the year when, here, there tends to be less rainfall. I then cover over the comfrey with some dried leaves and other carbon rich material, which keeps the bed neat and suppresses weeds to a degree. I have achieved good yields with this mulch material in the past and hope to again this year.
Grass clippings for first ‘earthing up’ can also work well in my. experience. Though some say that adding a mulch too rich in nitrogen might encourage too much foliage growth, I add it in thinner layers with carbon rich materials and more diverse green mulch materials and have obtained good yields in the past with this mulch too.
Another mulch material which I have found to be beneficial in the past is seaweed. When I get down to the local seashore, which is around 4 miles away, I sometimes collect some to use in the garden. The seaweed also seems to promote healthy tuber growth. But the only thing is that it does not break down as quickly in my experience, and so the harvest is not quite so easy when the time comes. While slugs are not a huge problem here I have also found that the seaweed retains moisture, and slugs like the damp conditions below the mulch. So one or two potatoes were a little slug damaged.
These are just my own experiences. You may find different mulches work best where you live. But perhaps my own experiments will inspire you to try new approaches in your own garden.