What is the temperature below zero for spinach? We need to build a greenhouse

Spinach needs to be covered with a greenhouse for insulation when the temperature is below minus 5 degrees Celsius. Spinach has strong cold resistance, but sustained low temperatures may cause frost damage, affecting growth rate and leaf quality. Spinach can tolerate temperatures ranging from minus 5 to minus 8 degrees Celsius in the short term, during which leaf cells lower the freezing point by increasing sugar concentration. If there is only a brief low temperature at night and the soil is not frozen, mature spinach usually does not require additional protection. But when low temperatures are accompanied by strong winds or snowfall, the leaves are prone to water loss and frostbite. It is necessary to cover them with plastic greenhouse film or non-woven fabric in advance, and the temperature inside the greenhouse can be increased by 3-5 degrees. Fields that have not yet sprouted after sowing require more protection, as young shoots may be damaged at minus 3 degrees Celsius. When the forecasted temperature remains below minus 10 degrees Celsius or an extreme cold wave occurs, it is necessary to take shelter measures. At this time, single-layer coverage may not be sufficient, and double-layer greenhouse film or small arch sheds can be added inside the greenhouse. Soil freezing can cause difficulty in root water absorption, and even after the temperature rises, leaf wilting may occur. It is recommended to set up a simple trellis for overwintering spinach in open fields in the north before winter to facilitate quick coverage. If the leaves have frozen, avoid immediately opening the shed and wait until noon to slowly warm up and thaw.

In addition to covering the shed, foliar spraying of potassium dihydrogen phosphate can be applied 3 days before low temperatures occur to enhance cold resistance, and stopping watering can reduce soil thermal conductivity. Clear the snow from the shed area in a timely manner after snowfall to avoid crushing the shed frame. In early spring, attention should be paid to the temperature difference between day and night inside the greenhouse. When the temperature exceeds 20 degrees Celsius during the day, ventilation and cooling should be carried out to prevent excessive leaf growth. It is recommended to choose cold resistant varieties based on local climate characteristics, such as round leaf spinach which is more resistant to freezing than pointed leaf varieties.