We have used hay to hill in the potatos. It seemed to work great. It kept the weeds down and made harvesting the potatos a whole lot easier. The only downfall was we harvested many of our potatos late and by the time we got to the potatos the mice and moles had invaded and munched a bunch of them. I think that if we did not wait until the late fall to harvest it would have been fine. I also think that a really heavy soil will hurt your yeilds and make harvesting a very difficult.

I have heavy clay soil as well, and tend to use my compost to hill them as a result. I have found that if you used soil that is heavy with clay in can be hard to dig around to find your potatoes. However, I still get potatoes even when I just use my heavy clay soil to mound them.

It really does not matter what you mound them with, some people use straw, chopped up leaves, soil, and so on. I often use pine needles mixed with compost. You could use potting soil, there is no problem with that, but there are probably cheaper alternatives.

Maybe I will have to see there is a local source that I can get my hands on some straw or hay. With the cat population around here I don't really worry about mice or moles...the only ones I've seen have been someone's dinner.

I have never had a problem with heavy clay and potatoes. I use a bit of compost when I plant the potatos but just hill them with what is in the garden.

Hint for larger potatos. ( I learned this by accident) When you potatos get ready to bloom, cut them back by about 1/3. The plant will put more energy into the tubers instead of the blossoms, thus making bigger potatos.
One year we got inundated by Colorad Potato beetles and no amount of work was gettng rid of them. So, I simply whacked the top third of the plants clean off and burned the cut off foliage along with those darned beetles. ( I don't spray chemicals on my food sources) We have been doing that ever since.

Helen

I have heard that horseradish planted with potatoes repels the Colorado Potato beetles. I am going to plant the horseradish in pots and place around the edges of my potato bin because I've heard it will spread like wildfire.