Purple potatoes owe their distinctive color to high concentrations of anthocyanins, the same water-soluble pigments found in blueberries and red cabbage. These compounds are distributed throughout the flesh, giving the tubers their striking appearance. Successfully harvesting these potatoes requires understanding the plant’s life cycle to ensure the best flavor, texture, and storage capability. The right time to dig depends on whether the goal is small, tender potatoes for immediate use or large, mature ones for long-term storage.
Timing the Harvest Window
The typical growth cycle for purple potatoes spans approximately 90 to 120 days from planting to full maturity. The exact harvest period offers flexibility depending on the desired outcome. Harvesting early yields “new potatoes,” which are small, delicate, and best for immediate consumption.
This early harvest can begin two to three weeks after the plant has finished flowering, signaling that small tubers have begun to form underground. These young potatoes have very thin skin that rubs off easily, making them tender but unsuitable for storage. For a larger, fully developed potato suitable for keeping over winter, the entire life cycle must be allowed to complete.
Visual Indicators of Maturity
The definitive signal that purple potatoes are ready for best flavor and long-term storage is vine dieback, or senescence. This natural stage occurs when the plant’s foliage begins to yellow, wither, and turn entirely brown. This signals that the plant has completed transferring energy and starches to the developing tubers below the soil.
Dieback is the crucial period when the potato skins “set” or harden, which defends against damage and rot in storage. For maximum skin set, wait an additional two to three weeks after the vines have completely died back before harvesting. A practical test involves gently unearthing a single potato and attempting to rub the skin with a thumb. If the skin resists peeling, the tuber is mature and ready for digging.
The Physical Harvest and Curing Process
Harvesting
Harvesting requires careful technique to prevent damaging the mature tubers, which compromises their storage life. A garden fork or broad-tined pitchfork is the preferred tool, reducing the risk of slicing compared to a shovel. Insert the fork into the soil at least six to eight inches away from the main stem of the dead plant.
Gently loosen and lift the soil, turning the entire hill over to expose the clustered potatoes. Separate any potatoes that sustain cuts or bruises and use them immediately, as they will not store reliably. Once dug, brush the potatoes free of excess soil but do not wash them. Keep them out of direct sunlight, which can cause them to turn green and develop a bitter flavor.
Curing
The next step for long-term storage is curing, which thickens the skin and allows minor abrasions to heal. Potatoes should be cured in a dark, well-ventilated space with a temperature range of 45 to 60 degrees Fahrenheit and high humidity (ideally 85 to 95 percent). This curing period should last for ten to fourteen days. Following the cure, the tubers are ready for long-term storage in a cool, dark environment, where temperatures remain between 40 and 45 degrees Fahrenheit.