Potatoes hate manure as it can give them potato scab so use compost with no manure, or even a mix of soil, leaves ,and old straw in the barrels. Add a slow release plant food like Osmocote to be sure that all the nutrients and micro nutrients are available. You can plant the tubers on top of the soil mix with just the barrel one third full of soil, then add more soil as the tubers sprout and the green leaves begin to grow taller. Keep adding soil around the necks of the new growth until the entire barrel is filled. Harvesting potatoes from a barrel is a lot easier than digging them up so you are on your way to being a backyard farmer without an aching back. I see some delicious potato salad in your future. Keep growing, Marianne Binetti