The process of growing potatoes culminates in the harvest, and timing significantly influences both the flavor and the storage life of the tubers. Unlike above-ground crops, determining readiness requires attention to the plant’s visible changes and an inspection of the underground crop. Harvesting at the appropriate stage ensures you develop the thick, protective skin necessary for successful long-term preservation. Understanding the difference between an early harvest for immediate consumption and a later one for winter storage is key to successful potato gardening.
Determining Maturity: New Potatoes Versus Main Crop
The decision of when to harvest potatoes is guided by the intended use, dividing the crop into two categories based on maturity. New potatoes are immature tubers harvested early, typically 55 to 70 days after planting. They have a delicate, thin skin that is easily rubbed off, making them tender and flavorful for immediate use. They should be consumed quickly, as their immature skin offers little protection for long-term storage.
Main crop potatoes, also called storage potatoes, are grown for maximum size and long-term keeping, requiring 90 to 120 days or more. These tubers fully mature underground, encouraging the development of a thick, durable skin. This tougher exterior protects the potato from moisture loss and disease, making it suitable for curing and storage throughout the winter months.
Key Indicators: When the Foliage Signals Readiness
For the main crop intended for storage, the most reliable indicator of readiness is senescence, which occurs above ground. This is the natural aging process where the potato plant’s vines begin to yellow, droop, and eventually die back completely. This signals that the plant has finished directing energy and starches from the foliage down to the developing tubers below the soil line.
After the foliage has completely died back, a waiting period of two to three weeks is necessary before digging. This time allows the potato skin to “set” or toughen. The skin firms up and adheres tightly to the flesh, which significantly reduces skinning and bruising during harvest. This process provides the barrier against pathogens and moisture loss necessary for successful storage. If vines remain green, growers can artificially induce senescence by cutting down the foliage, starting the skin-setting window.
The Final Step: Performing the Test Dig
The most definitive method for confirming main crop readiness is the test dig, which allows for a physical inspection of the skin set. To perform this, carefully excavate a single plant using a garden fork placed well outside the plant’s center to avoid damaging the tubers. Gently lift the soil and tubers, brushing away enough dirt to expose the potatoes. The primary check is determining if the skin has fully set, a requirement for long-term storage.
Take one of the larger tubers and rub the skin firmly with your thumb. If the skin easily rubs off or “slips,” the potato is not yet mature enough for keeping, and the crop should remain in the ground for another week or two. Skin slippage indicates the periderm layer is immature and susceptible to injury and decay. If the skin is firm and resists rubbing off, the tubers have achieved sufficient maturity and skin set, signaling the entire crop is ready for harvest.
Preparing Potatoes for Long-Term Storage
Once the test dig confirms a firm skin set, the harvested main crop requires specific post-harvest steps to maximize shelf life. The first step is curing, a process that allows minor scrapes or bruises incurred during digging to heal over. Immediately after harvest, gently brush off excess soil, but avoid washing the tubers, as moisture can encourage rot.
Curing is best achieved in a dark, well-ventilated space with temperatures of 50 to 60°F and high humidity (90 to 95%). This environment should be maintained for 10 to 14 days, allowing wounds to form a protective layer of cork cells (suberization). Following curing, potatoes are ready for final storage in a cool, dark location, such as a root cellar. Temperatures should be maintained around 40 to 50°F with high humidity to prevent shriveling. Avoid placing potatoes near fruits like apples, which release ethylene gas that encourages premature sprouting.