The Kennebec potato is a mid-to-late season, white-fleshed variety valued for its high yields and culinary versatility. It has smooth, light-tan skin and a creamy white interior, making it excellent for baking, mashing, and French fries. Kennebec plants grow vigorously and are resistant to diseases like Potato Virus Y and net necrosis. The tubers possess superior storage qualities, allowing the harvest to be enjoyed for many months.
Preparing Seed Potatoes and Soil
The process of “chitting,” or pre-sprouting the seed potatoes, should begin four to six weeks before the anticipated planting date to give the crop a head start. Place the seed potatoes in a single layer with the end containing the most “eyes”—small indentations where sprouts emerge—facing upward. Keep them in a cool, bright, but indirectly lit location, such as a porch or garage, where temperatures remain between 45°F and 55°F. This encourages the development of short, sturdy, deep green or purple sprouts, rather than long, weak white ones.
If using larger seed potatoes, cut them into pieces roughly 1.5 to 2 ounces in weight, ensuring each segment contains at least one or two healthy eyes. After cutting, allow the pieces to dry and form a protective, cork-like layer, known as callusing, for 24 to 48 hours before planting. This step prevents the cut surface from rotting in the soil and protects the seed piece from pathogens. Small, whole seed potatoes, often referred to as B-sized, should be planted without cutting.
Kennebec potatoes thrive in loose, well-drained, and moderately fertile soil with a slightly acidic pH range of 5.8 to 6.5. Soil preparation should involve deep loosening, ideally down to 10 to 12 inches, to accommodate the developing tubers and allow for proper drainage. Incorporating aged compost or other organic matter improves soil structure and provides a slow-release source of nutrients. Avoid using fresh manure or lime near planting time, as these can increase the likelihood of potato scab.
Timing and Technique for Planting
The optimal planting time for Kennebec potatoes is in early spring, typically two to four weeks before the average date of the last hard frost. Waiting for the soil to warm is important, as planting too early into cold, wet soil can cause the seed pieces to rot before they sprout. The soil temperature should be at least 40°F, but ideally above 50°F, for successful germination and initial growth.
The trench method facilitates the hilling process later in the season. Dig trenches 6 to 8 inches deep in your prepared soil, ensuring rows are spaced about three feet apart to allow for hilling and air circulation. Place the prepared seed pieces into the trench with the eyes facing upward, positioning them 10 to 12 inches apart within the row.
Once the seed pieces are placed, cover them with only two to three inches of soil, leaving the rest of the trench open. This shallow initial covering encourages the development of a strong root system and a greater number of stolons, which are the underground stems on which the new potatoes form. A low-nitrogen, high-phosphorus fertilizer can be sprinkled lightly into the trench to promote vigorous root and tuber growth.
Essential Post-Planting Care
Hilling, which involves mounding soil up and around the stems, is the primary maintenance practice for potatoes. Hilling serves a dual purpose: it prevents developing tubers from being exposed to sunlight, which turns them green and inedible, and it encourages the plant to produce more potatoes higher up the stem. The first hilling should occur when the shoots emerge and reach a height of six to eight inches.
Carefully draw soil from between the rows or from the sides of the trench and pile it up around the stems, covering about two-thirds of the plant’s height. Repeat this process every few weeks as the plant grows another six to eight inches, continuing until a final mound of 10 to 12 inches high is formed. This continuous mounding also helps suppress weed growth, which competes with the potato plants for moisture and nutrients.
Kennebec potatoes require consistent moisture, particularly from the time the plants begin to flower through the main period of tuber formation. Aim to provide the plants with one to two inches of water per week, especially if rainfall is insufficient. Inconsistent watering, such as alternating between dry spells and heavy soaking, can cause internal defects in the tubers like hollow heart or growth cracks.
While Kennebec is known for good disease resistance, vigilance against common pests and diseases is necessary. Monitor the foliage closely for signs of the Colorado potato beetle, which can quickly defoliate a plant, or the presence of late blight, a fungal disease that rapidly destroys leaves and stems. Proper crop rotation, avoiding planting potatoes in the same spot for at least three to four years, is the most effective cultural practice for minimizing disease pressure.
Harvesting and Curing
For a mature main crop of Kennebec potatoes, harvesting typically occurs 90 to 110 days after planting, timed by the plant itself. Wait until the foliage naturally begins to yellow and die back completely, signaling that the tubers have finished growing and the skins are setting. Allowing the dead foliage to remain for two weeks helps to toughen the skins, which is essential for maximizing storage life.
To harvest, use a garden fork to gently lift the entire plant, starting about 12 to 18 inches away from the main stem to avoid puncturing the tubers. Carefully loosen the soil and lift the potatoes out, taking care not to bruise or damage the thin skin. Any potatoes that are nicked or cut during digging should be set aside for immediate consumption, as they will not store well.
After harvesting, the potatoes must undergo a curing process to heal abrasions and set the skin for long-term storage. Lay the unwashed tubers in a single layer in a dark, well-ventilated location with high humidity (ideally around 90 percent) and a temperature between 50°F and 60°F. Allow the potatoes to cure for 10 to 14 days to extend their shelf life. Following the cure, Kennebec potatoes should be stored in a dark, cool environment (40°F and 45°F) to prevent sprouting.