By B. Rosie Lerner
Extension Consumer Horticulture Specialist, Purdue University
Chances are that some dedicated gardeners have already tilled their gardens and planted their "seed" potatoes. Some gardeners aim for planting on or around St. Patrick's Day, while some of us will be lucky to have them planted by Mother's Day!
Because our weather can be so unpredictable, it's hard to be any more precise when advising on planting time. Potatoes are considered to be a cool-season crop and can be planted just as soon as the ground has thawed and dried enough to safely work the soil. It is critical to allow the soil to dry adequately. If worked while it's still too wet, soil becomes hard and compacted, leading to long-term frustrations for the eager gardener.
The potato plant can adapt to most types of soil, but must have good drainage to prevent the tubers from rotting before they can be harvested. Choose a sunny location and work in 2-3 pounds of a balanced, low-analysis fertilizer, such as 12-12-12, per 100 square feet to promote vigorous plant growth.
The part of the potato plant that we eat is called a tuber, a technical name that refers to an enlarged modified stem that grows underground. Potato tubers that are used to create a new planting are called seed potatoes. You'll want to start with the best quality seed potatoes, so look for those that are labeled as "certified disease-free" at garden shops and in mail-order catalogs.
To start a new planting, cut the seed potato into pieces so each individual piece has at least one healthy-looking bud (often called an "eye"). That bud will become the shoot of the new plant and, as the stem develops, it also will produce new roots. The piece of tuber attached to the bud provides a source of carbohydrates to sustain the young plant until those new roots and shoots develop. Plant the pieces 2-3 inches deep, space them about 12 inches apart within the row, and leave 24-36 inches between rows.
New tubers that will become this year's harvest generally begin to form sometime in early to mid-summer and continue to grow in size until early fall, as long as adequate moisture, air and nutrients are available.
The tubers can be harvested as "new" potatoes in mid- to late summer, before they reach full size and before the skins start to toughen. New potatoes are tender and tasty, but they don't keep very long. Since the plant must be pulled up to harvest the tubers, yields are generally small.
If you want bigger yields of full-size tubers, it's best to leave the plants until they begin to die back on their own, usually by late summer or early fall. As the plants begin to turn brown, gently lift the tubers with a digging fork and remove them from the plants. If the potatoes are going to be used immediately, no further treatment is needed. However, to be able to store the potatoes for later use, you'll want to allow the tubers to "cure," or air-dry, for 1-2 weeks to allow the skins to thicken and dry.
The biggest challenge for gardeners is finding dark storage conditions at a temperature of 40 F to 45 F. Both light and warmth promote sprouting of the buds. For best results, store only the best quality tubers that are free of cuts, bruises and diseases. Potatoes can be stored from two to nine months, depending on the cultivar and storage conditions.
