Answer: Most likely, your plants were suffering from some sort of disease. Potatoes are succeptible to many fungal and some bacterial diseases. To reduce the problem, rotate them to a different bed each year.
Potatoes prefer an acid soil with a pH of around 5.5 to 6. Mix some compost into the soil before planting and go easy on the manure, which can encourage potato scab. Since too much nitrogen will promote foliage growth at the expense of tuber growth, stick to fertilizers such as phosphate rock and greensand to provide nutrients.
Plant seed potatoes about 12" apart in rows 2 1/2' apart. (If your seed potatoes are large--say, larger than an egg, you can cut them into pieces before planting. Just be sure each piece has 2 or 3 eyes. Allow the cut potatoes to dry overnight before planting.) I like to plant in trenches about 6" deep, covering the seed potatoes with about 2" of soil.
Hilling potatoes encourages production of more tubers. When the plants reach about 6" tall, mound soil or mulch around the base of the plants within 1/2" of the lower leaves. (You'll be filling in the trench, if you made one.) Repeat this process several times throughout the summer.
Hope the above helps you identify where you might have gone wrong, and inspires you to try growing potatoes again.
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