Wisconsin’s distinct climate and sandy soils make it a premier potato-growing region. For home gardeners, understanding the correct harvest time is the most significant factor in determining the quality and shelf life of the crop. Since potatoes grow underground, the optimal harvest time depends entirely on the gardener’s goal for the tubers. The choice is primarily between harvesting young potatoes for immediate use or mature potatoes for long-term storage.
Understanding New Versus Storage Potatoes
The decision of when to harvest depends on the final product: a new potato or a storage potato. New potatoes are young tubers harvested before full maturity, characterized by their small size, delicate flavor, and thin skin. Because their skin is immature, they have a short shelf life and must be consumed quickly after harvest.
Storage potatoes remain in the soil until the plant’s life cycle is complete, allowing them to reach full size and develop a tough, thick skin. This mature skin is necessary for the curing process, which permits long-term storage through the winter. Since most Wisconsin gardeners plant seed potatoes in late April or early May, this choice dictates a harvest timeline spanning the entire growing season.
Reading the Plant Visual Indicators
The potato plant provides the clearest signals for when to begin harvesting. For new potatoes, the best time to dig is about two to three weeks after the plant begins to flower. At this stage, the vines are still green and vigorous, and the tubers are small and tender. Gardeners can carefully dig near the plant to harvest a few small potatoes, leaving the rest to continue growing.
For storage potatoes, the gardener must wait until the foliage, or vines, have completely died back. This visual cue, known as senescence, signals that the plant has finished transferring energy to the underground tubers. It is important to wait at least two weeks after the vines have yellowed and wilted to allow the potato skins to “set” and toughen up.
Before harvesting a large batch, perform a “skin set” test by rubbing a small area of the skin with your thumb. If the skin does not easily rub or peel off, the potatoes are mature and ready for long-term keeping.
Essential Steps for Digging and Curing
Once indicators confirm the potatoes are ready, the actual digging and immediate post-harvest handling are crucial for quality. Always harvest on a dry day, as dry soil prevents the spread of diseases and makes the process cleaner. Use a garden fork or shovel, inserting it well away from the center of the plant to avoid piercing or bruising the tubers.
After gently lifting the potatoes, leave them on the soil surface for a few hours to allow the skin to dry and clinging soil to loosen. Keep freshly dug potatoes out of direct sunlight, as exposure causes them to turn green and develop solanine.
The next step is curing, which involves gently brushing off excess soil; never wash the potatoes. Store them in a dark, humid, and moderately warm environment, ideally between 45°F and 60°F, for two weeks. This curing period allows minor wounds to heal and the skin to thicken, preparing the tubers for long winter storage.