The optimum soil temperatures for good growth range from 55-70 degrees F. A week or two before your planned potato planting date, set your seed potatoes somewhere where they will be exposed to some warmth (between 60 and 70 degrees F) and lots of light. This will induce them to begin sprouting. A day or two before planting, use a sharp, clean knife to slice the larger seed potatoes into “seeds”. Each seed should be approximately 1½-2 inches square, and must contain at least 1 or 2 “eyes” or buds. Smaller potatoes may be planted whole. In the next day or so, your seed will form a thick callous over the cuts, which will help to prevent it from rotting once planted.
Traditionally potatoes are grown in rows. The potato seeds are planted every 15 inches, with the rows spaced 2½-3 ft apart. If space is limited or if you would only like to grow a small crop of potatoes, you may prefer to plant one or two potato mounds. Each 3-4 ft diameter mound can support 6 to 8 potato plants. With either method, the first step is to cultivate and turn the soil one last time before planting, removing any weeds, rocks or debris. This will loosen the soil and allow the plants to become established more quickly. Your potato plants will benefit from the addition of compost, well composted manure, and other organic matter to the soil.
Planting in Rows: Dig a shallow trench about 4 inches wide and 6-8 inches deep. The spacing at which you place the seed pieces will determine the harvested potato size. For most household uses, you will want to plant your potato seeds 15 inches apart in this trench. If you’d like a quick crop of “baby” potatoes for soups and stews, you can plant the seeds 4 inches apart, and begin harvesting them as soon as they reach the desired size. Place the potato seeds into the trench with the cut side down and then cover them with 3-4 inches of soil. Do not fill the trench completely with soil.
Depending on the soil temperature, the sprouts will begin to emerge in about 2 weeks. At this time add another 3-4 inches of soil. Your crop of potatoes will form between the seed piece, and the surface of the soil. For this reason, when the stems are about 8 inches high, you once again add enough soil to bring the level half way up the stem of the plant. Another hilling will be needed 2-3 weeks later, at which time you again add soil half way up the stem of the plant.
After these initial hillings, it is only necessary to add an inch or two of soil to the hill each week or so, to ensure there is enough soil above the forming potatoes that they don’t push out of the hill and get exposed to light. If the new potatoes are exposed to sunlight while they are developing, they will turn green (which may be toxic). This hilling process is necessary to create sufficient space for the potatoes to develop large tubers, and an abundant crop. Don’t get carried away with hilling though…if you cover up too much of the foliage, you may end up reducing your final crop yield.
Mound Planting: The basic procedure for planting potatoes in mounds is the same as for planting in rows. The difference here is that you can grow your crop in a more confined area, or take advantage of an otherwise unused area of the garden. Cultivate and loosen the soil where your potato mound will be. Designate the approximate perimeter of your planting circle, which should be about 3-4 feet in diameter. Space 6-8 potato seeds evenly around your circle, and cover with the initial 4 inches of soil. Continue the same procedures as you would for planting in rows.
Watering & Care: For the maximum crop, keep your potato vines well watered throughout the summer, but especially during the period when they are in flower, and immediately thereafter. This is the time when the plant is creating the new tubers, and water is critical. Water early in the day so that the foliage has time to dry completely before evening. (Wet foliage can make your plants more susceptible to several potato diseases.) When foliage turns yellow and dies back, discontinue watering to allow the tubers to “mature” for a week or two before harvesting.
Once the vines have passed the critical watering stage while in flower, they will tolerate a certain amount of drought. According to some studies, non-irrigated potatoes are less watery and more healthful. However, potato plants which are not watered regularly will produce a much smaller crop.
Potato Harvest: You may begin to harvest your potatoes 2-3 weeks after the plants have finished flowering. At this time you will only find small “baby” potatoes if you were to dig up a plant. Potatoes can be harvested any time after this, by gently loosening the soil, reaching under the plant, and removing the largest tubers, leaving the smaller ones to continue growing. If you want late potatoes for storage, wait 2-3 weeks after the foliage dies back. Carefully begin digging a foot or so outside of the row or mound. Remove the potatoes as you find them.
If the weather is dry, allow the potatoes to lay on the soil surface, unwashed, for 2-3 days so they can dry. If the weather is wet, or rain is expected, move the harvest to a cool, dry area (like a garage or basement) for the drying period. This drying step is necessary to mature the potato skin, which will protect the potato during storage. If by the end of September, the plants have not begun to die back, all of the foliage should be cut off to ensure your crop has ample time to mature before winter. Store your undamaged potatoes in a well-ventilated, dark, cool (about 40 degrees) location. Properly dried and stored potatoes should keep well for three to six months.