Gardeners seeking a head start on the growing season often use methods of warming the soil in early spring. Potatoes are a cool-season crop that you can plant outdoors in a garden approximately three weeks prior to the final spring frost. Help your potatoes mature faster by planting them under black plastic mulch. The black plastic will warm the soil and you can harvest the potatoes through the plastic when they are mature.
Cultivate the garden soil where you will grow the potatoes. Work the soil 6 inches deep with a garden fork. Add 4 inches of compost over the cultivated soil and work the soil in thoroughly with the garden fork. Add 1.5 lbs. of fertilizer over the soil for every 100 square feet of planting area and work the fertilizer in well with the garden fork.
Spread the black plastic sheeting over the planting area, stretching it flat over the soil. Anchor the edges of the plastic sheeting with large rocks or bricks.
Prepare the potatoes for planting. Each potato piece must have at least one eye and should weigh a minimum of 2 oz. Cut large seed potatoes into smaller pieces if the tubers are large and have multiple eyes.
Create rows for the potato seeds by cutting slits in the black plastic with a utility knife. Cut rows 2 to 3 feet apart. Plant the potatoes 1 foot apart in the prepared rows and cover the potatoes with 2 inches of soil.
Add additional shredded mulch around the potatoes to insulate them further--approximately 4 inches around each seed potato is adequate.
Water the newly planted potatoes immediately after planting them. Provide up to 2 inches of water each week.
Fertilize the potatoes with a nitrogen fertilizer (34-0-0) approximately six weeks after they sprout. Use ¼-lb. of fertilizer for every 100 square feet of row, sprinkling the fertilizer approximately 2 inches away from the plants. Cultivate the soil lightly with a hand rake to incorporate the fertilizer into the soil. Water the soil immediately after fertilizing.
Leave the plastic in place until after you harvest the potatoes. The plastic not only serves to warm the soil, but will prevent weed growth as well. Harvest potatoes when they are as large as you desire.