Potatoes are a fundamental food crop around the world, providing sustenance and versatility in the kitchen. Determining the precise moment to lift potatoes from the soil directly impacts their flavor, texture, and ability to be stored long-term. Knowing what your plants look like when they are ready prevents harvesting immature potatoes or leaving mature ones in the ground too long, ensuring you maximize the potential of your crop.
The Visual Cues of Maturity
The most noticeable indicator that a potato plant has finished its underground work is foliar senescence, or the dying back of the leafy top growth, often called the haulm. The vibrant green leaves begin to yellow, wilt, and eventually turn brown and collapse. This visual change signals that the plant has ceased its vegetative growth and has redirected all its energy into the tubers below, which are now bulking up and maturing.
For potatoes intended for storage, simply seeing the foliage die back is not the final sign of readiness. A waiting period is necessary for a process called “skin set” to occur, which is the hardening of the tuber’s outer layer. This period typically requires leaving the potatoes in the ground for an additional two to three weeks after the haulm has completely withered.
You can perform a simple “rub test” on a sample potato to determine if the skin has set properly. Gently brush the soil from a potato and rub its skin with your thumb. If the skin remains firmly attached and does not rub or peel off easily, the potato is mature and ready for long-term storage. Immature potatoes, by contrast, will have a thin skin that easily slips off, exposing the flesh beneath.
Harvesting New Potatoes vs. Storage Potatoes
The intended use of the potato dictates the optimal harvest time, creating a clear distinction between new and storage varieties. “New potatoes” are actually just immature tubers of any variety, harvested early in the growing season, typically around 60 to 70 days after planting. These are lifted while the plant is still green and often flowering, before the skin has had a chance to fully thicken.
These young potatoes possess a tender skin and a delicate flavor, but their thin periderm means they do not store well and must be consumed within a few days of harvest. Storage potatoes, on the other hand, require a longer growing period, usually 90 to 120 days, to reach full maturity. This extended time allows the tubers to maximize their size and accumulate the starches necessary for long-term preservation.
Storage potatoes must only be harvested after the foliage has died back completely and the skin set test confirms a tough, protective outer layer. The fully matured skin acts as a natural barrier against moisture loss and disease.
The Physical Harvesting Process and Curing
Once readiness is confirmed, especially for storage potatoes, it is best to harvest on a warm, dry day when the soil is not overly saturated. Using a garden fork rather than a spade minimizes the risk of slicing or damaging the tubers, which can lead to rot in storage. You should begin digging approximately 12 to 18 inches away from the center of the dead plant, carefully lifting the entire hill to expose the potatoes.
Handle the harvested tubers with gentleness, as any bruising or cutting creates entry points for pathogens. After lifting the potatoes from the soil, brush off the majority of the loose dirt but avoid washing them, as moisture encourages spoilage. Any potatoes that have been nicked or damaged during the digging process should be set aside for immediate consumption.
Curing for Storage
The final, non-negotiable step for long-term storage is curing, a process that hardens the skin and allows minor scrapes to heal. Curing involves placing the potatoes in a dark, well-ventilated area with high humidity, ideally between 45°F and 60°F, for a period of seven to ten days. This brief post-harvest treatment ensures the skin is fully toughened, preparing the potato for a much longer dormancy period in the storage environment.