Growing potatoes in Minnesota requires precise planting timing due to the state’s short and often unpredictable growing season. Potatoes are planted from specialized seed tubers, not true seed, making their initial cultivation a calculated risk. To ensure a productive harvest, gardeners must balance planting early enough to maximize the cool growing period with the danger of exposing the seed pieces to lingering cold and overly wet soil, which can lead to rot. Mastering the planting date, preparing the seed properly, and utilizing the technique of hilling are coordinated steps that maximize yield in this northern climate.
Determining the Ideal Planting Window in Minnesota
The optimal time to plant potatoes is not a single calendar date but a window determined by specific environmental conditions. Potatoes are a cool-season crop, meaning they thrive in the moderate temperatures of spring. The ground must be workable and have warmed to a minimum of 45°F, with an ideal range of 45°F to 50°F, before planting should begin.
In Southern Minnesota, including the Twin Cities area, the soil often reaches this temperature range by early to mid-April. Gardeners in this region can typically plant two to four weeks before the average last spring frost date. Planting later shortens the period for tuber development, especially since temperatures above 75°F can inhibit the formation of new potatoes.
Moving north, the planting window shifts later due to persistent cooler temperatures and a later average last frost. Planting too early in cold, saturated soil creates a high risk of the seed pieces rotting before they have a chance to sprout. Therefore, the soil thermometer, rather than the calendar, is the most reliable tool for deciding when to begin planting across Minnesota’s varied geography.
Essential Steps for Seed Potato Preparation
Before a seed potato is placed into the soil, specific preparation steps must be followed to ensure a strong, disease-free start. It is recommended to use certified seed potatoes, which are guaranteed to be disease-free, rather than relying on grocery store potatoes that may carry pathogens or be treated with sprout-inhibiting chemicals. A process called “chitting” or pre-sprouting is beneficial, especially for an earlier harvest.
Chitting involves placing the seed potatoes in a bright, cool, frost-free location, ideally around 50°F, for about six weeks before planting. This exposure encourages the development of short, sturdy, dark-colored sprouts, activating the tuber’s growth process. Larger seed potatoes must be cut into smaller pieces, each weighing approximately 1.5 to 2.0 ounces, which is roughly the size of a golf ball.
Each cut piece must contain at least one or two “eyes,” the buds from which the plant will grow. The freshly cut surfaces must then be cured for one to two days at room temperature, around 60°F to 70°F, in a humid environment. This curing process allows the cut surface to “heal” and form a protective, leathery layer (callus), which significantly reduces the risk of rot and disease infiltration once planted in the soil.
Planting Depth, Spacing, and Hilling
The physical planting process requires attention to both the initial depth and the subsequent care technique known as hilling. Seed pieces should be planted with the cut side facing down, resting in a furrow or hole that is initially three to five inches deep. Adequate space is required to allow for proper plant development and tuber expansion beneath the soil surface.
Spacing the seed pieces about 10 to 12 inches apart within the row is standard practice for most varieties, with rows separated by 30 to 36 inches. Closer spacing can be used if the goal is harvesting smaller, “new” potatoes, while wider spacing encourages the growth of fewer, but larger, tubers.
As the plants grow, the practice of hilling begins once the green shoots reach about six to eight inches in height. Hilling involves drawing up loose soil or organic matter around the base of the plant to form a mound. This process is repeated periodically throughout the growing season, covering the stems and leaving only the top leaves exposed. Tubers develop on underground stems called stolons, and hilling encourages the plant to form more stolons, resulting in a larger yield. Hilling also protects the developing potatoes from exposure to sunlight, which causes them to turn green and produce a bitter compound called solanine.