Potatoes are a staple crop derived from the plant Solanum tuberosum, which is a tuber-producing perennial. Potato plants are not frost tolerant, as the above-ground foliage is highly susceptible to cold injury. This sensitivity is particularly pronounced in tender, newly emerged shoots during the spring planting season. The underground tubers, however, possess greater protection from brief drops in air temperature.
How Potato Plants React to Freezing Temperatures
The potato plant is vulnerable due to the high water content within its leaves and stems. When the air temperature drops below freezing, the water inside the plant’s cells turns to ice, which expands and causes the cell walls to rupture. This cellular damage leads to the rapid collapse of the leaf tissue.
The critical temperature threshold for cultivated varieties of potato is quite low, with damage possible when the air temperature dips just below 32°F (0°C). Cultivars of Solanum tuberosum are often severely damaged or killed if the temperature drops to around 27.5°F (-2.5°C) or lower for a sustained period. Even a temperature slightly below freezing, such as 30.6°F (-0.8°C), can cause chilling damage that impairs the plant’s function without immediately killing the tissue.
The potato tuber is far less vulnerable to frost damage than the aerial foliage. The surrounding soil acts as an insulator, protecting the developing tubers from the cold air temperature. Tubers are only at risk if the ground itself freezes solid, which typically requires a very hard, prolonged freeze well below 28°F (-2°C). If tubers are exposed near the soil surface, they can suffer damage, which often manifests as a gray or reddish-brown discoloration in the flesh.
Recognizing and Addressing Cold Weather Damage
Frost damage is easy to identify by its visual appearance. Affected leaves initially look limp and water-soaked, quickly turning black or dark brown as the damaged tissue collapses. The worst-affected areas are generally the top leaves and the outer edges of the plant canopy where the cold air first makes contact.
A severe frost can kill the above-ground growth down to the soil line. Fortunately, the potato plant has a strong recovery mechanism, provided the underground seed potato is undamaged. The plant uses the energy stored in the seed tuber to generate new shoots from the unaffected parts of the stem below the soil.
Gardeners should resist the urge to cut back the damaged foliage after a frost event. Wait approximately 10 to 14 days to fully assess the extent of the injury. If the main stem below the soil line remains intact, the plant will typically send up new, healthy growth, negating the need to replant. If new shoots fail to emerge, gently check the seed potato to ensure it did not rot due to overly wet or cold soil conditions.
Strategies for Frost Prevention and Protection
Proactive steps are the most effective way to manage the risk of frost damage to potato plants. Gardeners should ensure planting occurs after the last anticipated spring frost date for their region. While the seed potato can be planted earlier, the shoots typically emerge within two to three weeks, making them susceptible to late cold snaps.
One of the most effective and traditional protective measures is hilling, which involves mounding soil up and around the base of the stems. If a late frost is forecast, mounding fresh soil over the emerging shoots completely will insulate the tender foliage and prevent direct contact with the freezing air. This method protects the lowest buds on the stem, which are the ones that will regenerate new growth if the tips are damaged.
For unexpected, short-duration frosts, temporary physical covers provide immediate protection. Floating row covers, old blankets, or even tarps can be draped over the plants to trap residual heat radiating from the soil. Watering the soil before the frost is expected can also help, as moist soil holds more heat than dry soil, radiating warmth that can slightly elevate the air temperature immediately surrounding the plants.