Overwintering tomato freeze injury
As winter deepens, temperatures in northern regions gradually drop, putting greenhouse-grown tomatoes through a severe cold test. Tomatoes are heat-loving crops with limited cold tolerance. During the winter and early spring seasons, especially during the deep winter, they are vulnerable to low temperatures and frost. When greenhouse temperatures remain between 5°C and 10°C for extended periods, the leaves may turn dark green or appear waterlogged. If the temperature stays consistently at 5°C, the leaf edges may lose their green color. In cases of sudden frost (temperatures below 2°C), the leaves may turn purple due to increased anthocyanin production, followed by wilting and even plant death. Prolonged exposure to temperatures below 5°C can cause chilling injury, leading to loss of green color and eventual plant death.
These symptoms often resemble those of magnesium deficiency, which occurs when plants lack magnesium, causing yellowing of the leaves. However, low temperatures and excessive nitrogen and phosphorus fertilizers can interfere with magnesium uptake, increasing the risk of deficiency. When leaf chlorosis appears during cold winters, the first consideration should be freezing damage rather than nutrient deficiency. Prolonged exposure to temperatures below 5°C can lead to chilling injury, causing the leaves to become bleached and the entire plant to die in severe cases. By analyzing the seasonal climate and reviewing management practices and insulation measures, it's possible to distinguish between freezing injury and nutrient deficiency. Prompt treatment based on symptoms can help reduce unnecessary losses.
To address freezing damage, selecting cold-resistant, low-light, and low-temperature-tolerant tomato varieties is essential. From the start of greenhouse management, improving insulation is key to preventing cold injury. Thickening the earth walls, increasing the density of straw or weeds, and using additional arch sheds can help raise temperatures and protect against the cold. In case of sudden frosts, temporary heating methods such as burning coal stoves or using space heaters can be effective. For chemical control, cold-resistant agents can be applied—such as 3.4% Bi Protect wettable powder diluted 5000–7500 times, or a mixture of 15 liters of water, 50 grams of brown sugar, and 0.3% potassium dihydrogen phosphate. Spraying these solutions can enhance plant resilience and minimize damage caused by cold stress.
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