Many gardeners pass up growing potatoes because they think they do not have enough room to grow these vigorous plants. The good news is, if you have room for a hay bale, you can grow potatoes in your own backyard with little effort.
Location 
Position the hay bales in an area that receives at least 6 to 8 hours of direct sunlight a day. Full day sun is preferred. Because the potatoes grow inside the hay bale, the bale can be positioned in areas where the soil is unsuitable for gardening or even on top of paved areas. However, water does drain from the bottom of the bale, so choose an area where this is not an issue.

Prep the Bales 
Saturate the hay or straw bales with water until it runs freely from the bottom of the bale. Repeat this procedure on days two and three. On the fourth day, sprinkle 1 cup of bone meal over the top of the bales and water thoroughly. Repeat the procedure for days five and six. On days seven, eight and nine, reduce the bone meal to ½ cup and water as usual. On day ten, sprinkle the bales with ½ to 1 cup of 10-10-10 fertilizer and water thoroughly. This speeds the decomposition process inside the hay bale and creates rich compost for growing.

Check the Bales 
Make holes in the hay bale by gently pulling the layers of hay open. Check that the inside of the bale is warm, but not hot. During decomposition, the insides heat as they begin to break down, but it should have cooled off by day 10. If the center feels hot to the touch, wait another day or two before planting the potatoes

Plant the Potatoes 
Cut the potatoes in two or more sections with at least two eyes on each section. Place the cut potatoes inside the bale to a depth of 250 mm spaced 150 – 300 mm apart along the hay bale. Typically, four potato plants fit in one bale. Close the hay over the potatoes.

Watering 
Water thoroughly until water runs freely from the bottom of the hay bale. The hay bales must be kept moist and may require daily watering. Running a soaker hose over the top or filling milk cartons with water and punching small holes in the bottom for water to drip onto the bales works well.

Fertilizer 
Apply water-soluble fertilizer designed for garden vegetables once a week. Because nutrients leach from the bottom of the hay bale, regular fertilizer is necessary to provide growing potato plants with the nutrients they need.

Harvesting 
Check for "new potatoes" once the potato plants bloom. Gently pull back the layers of hay and harvest young potatoes. Close the layers and allow small potatoes to continue to grow. Harvest mature potatoes in the fall once foliage dies back.

Potatoes grown in hay bales a clean and free of soil, but the best part is the ability to harvest tender new potatoes as soon as they "set on" without disturbing the roots of the plants.

All in one handy file. How to grow, when to grow seed types and seed raising mix