What are the common methods for freeze protection of greenhouse vegetables without heating?

Now it is the cold winter season, which is a test of survival for many kinds of vegetables. So in the case of a greenhouse, how can some common and effective methods be adopted without heating to ensure, to a certain extent, that the vegetables can grow normally? What are the common methods for freeze protection of greenhouse vegetables without heating?

1. Multi-layer film covering

A single layer of greenhouse film has poor insulation performance. When the outside temperature is low, freeze damage can occur once the temperature inside the greenhouse reaches around 0°C. Therefore, multiple layers of film are needed to ensure the temperature inside the greenhouse. That is, achieve “three films and one curtain” covering, namely covering the greenhouse film, small greenhouse film, plastic mulch, and adding straw curtains on top of the greenhouse. When the outside temperature drops to -5°C, freeze damage generally will not occur inside the greenhouse.

2. Prepare heat-generating soil

Use chicken manure, heat-generating organic fertilizer, cow manure and other air-permeable fertilizers to prepare heat-generating soil. That is, after they are decomposed, take 20% of each, mix with 60% dry fine soil. This kind of nutrient soil has good heat absorption and heat generation performance, giving vegetable seedlings a good growth environment, with more and longer roots, strong absorption function, and robust vegetable growth, naturally with strong cold resistance.

3. Control nitrogen fertilizer application

During the seedling stage, appropriately reduce the amount of nitrogen fertilizer. Never apply chemical nitrogen fertilizer in a one-sided way, so as to avoid poor cold resistance of vegetables. Topdressing should be early to promote sturdy vegetable seedlings. Quick-acting nitrogen fertilizer must not be applied before low temperatures; it is advisable to apply phosphorus and potassium fertilizer once to enhance cold resistance. In winter, light is weak and the fertilizer uptake capacity of vegetables is poor. Spraying photosynthetic micro-fertilizer on the leaves can prevent deficiency symptoms caused by insufficient nutrient absorption by the root system. At the same time, growth hormones should be used less or not at all, to prevent tender growth and reduced cold resistance.

4. Supplement carbon

For vegetables cultivated in greenhouses, 1 hour after the sun comes out, the carbon dioxide produced by nighttime plant respiration and soil microbial decomposition can be absorbed, after which they are in a state of carbon starvation. Therefore, when encountering sunny weather with high temperatures, the greenhouse film can be opened and closed repeatedly to let in outside carbon dioxide, so as to improve the cold resistance and yield of vegetables. When the temperature is low, keep the greenhouse closed. Artificially supplementing carbon dioxide in winter can improve cold resistance and increase yield.

5. Shallow intertillage for insulation

When the vegetable plot surface is compacted, the entry of daytime heat into the tillage layer is restricted, so heat storage decreases. In addition, cracks are large and deep, the soil aggregate structure is poor, heat is easily lost in the first half of the night, and the greenhouse temperature is low in the second half of the night, which can easily cause chilling injury. If shallow intertillage is carried out on the greenhouse soil, it can break up compaction and fill cracks. It can not only control groundwater transpiration from carrying away heat, but also preserve soil moisture and temperature, preventing cold and protecting seedlings.

6. Irrigate fully to prevent freezing

Freeze damage to vegetables in winter is mostly caused by lack of water. Because water has a higher specific heat than air and releases heat slowly, if the soil moisture content is moderate, the pores and cracks in the tillage layer are fine and dense, and the root system is not suspended in air, the soil insulation performance can be improved, and the root system will not suffer freeze damage. Therefore, for greenhouse vegetables, irrigating fully before winter or irrigating fully on a good weather day during winter has a good freeze-prevention effect.

7. Raise seedlings in nutrient pots

Use black plastic nutrient pots for seedling raising. During the day they absorb heat, preserve warmth, and protect roots. When the outside temperature is below zero, and the bed surface temperature inside the greenhouse is around 5°C, the temperature inside the nutrient pots can reach around 8~10°C. Vegetable seedlings can grow slowly without freeze damage.

8. Drench roots with rooting hormone

For greenhouse vegetables overwintering, after using rooting hormone, the root system can increase by about 60%, and root depth can increase by about 25%. With a well-developed root system and strong absorption capacity, seedlings will not suffer freeze injury due to poor cold resistance caused by lack of water or nutrients.

In addition, if conditions permit, it is best to use galvanized steel pipe greenhouses. For the greenhouse film, it is best to use anti-drip film; for ordinary film, polyethylene film is preferable. Building materials and walls can be whitewashed, which can increase reflected light and extend service life. Appropriately increasing the height of the greenhouse can also improve the light conditions inside the greenhouse.