Potatoes are a staple crop worldwide. The potato is botanically a tuber, a swollen underground stem designed to store the plant’s energy reserves. This tuber enlargement is the growth phase that gardeners and farmers monitor closely. The question of when this underground growth stops is answered by observing a specific signal from the plant itself.
The Physical Signal of Growth Cessation
Tuber growth ceases when the potato plant’s foliage undergoes senescence, or natural die-back. This is the clearest physical signal that the potato has stopped enlarging and is ready for harvest. Visual cues begin with the green leaves and stems yellowing, turning brown, and eventually collapsing entirely. This process indicates a biological shift where the plant stops channeling sugars from photosynthesis into the tubers. The plant prepares existing tubers for their dormant phase.
The vine die-back allows the tuber skins to harden, a process called “setting,” which improves long-term storage quality. To ensure maximum size and maturity, wait about two weeks after the vines have completely died back before harvesting. This waiting period ensures the skin is fully set and the growth cycle is complete.
Distinguishing Between New and Mature Potatoes
Although vine die-back signals that tuber growth has ceased, potatoes can be harvested at different stages for distinct culinary purposes. Tubers harvested early, before the vines die back, are known as “new potatoes.” These immature tubers are small and have a thin, delicate skin. New potatoes are prized for their high moisture content and tender texture, but their thin skins mean they must be consumed quickly and are not suitable for long storage.
In contrast, “mature potatoes” are harvested after the vines have completely died and underground growth has stopped. This timing allows the tubers to reach maximum size and develop a thick, protective skin. Mature potatoes are the type intended for winter storage, as the thick skin prevents moisture loss and protects the tuber from damage.
The Post-Growth Phase
Once mature tubers are removed from the soil, the post-growth phase focuses on preparing them for storage through curing. Curing allows the potato’s skin to thicken further and minor nicks or cuts sustained during harvest to heal. This healing process is known as suberization, where a protective layer forms over wounds.
Ideal curing conditions involve placing the potatoes in a dark, well-ventilated area with high humidity (85 to 95 percent) and a moderate temperature (45 to 60 degrees Fahrenheit). This environment should be maintained for one to two weeks. Successful curing improves storage life by reducing moisture loss and minimizing the potential for rot. After the skin has fully toughened, the potatoes can be moved to a cooler, dark environment, ideally 40 to 45 degrees Fahrenheit, for long-term storage.