How to control temperature in greenhouses

Vegetables have different temperature requirements in different growth stages. If you want to control the temperature well, you must first master the characteristics of vegetables. Choose appropriate temperature management based on its characteristics.

1. Lower the temperature before planting to strengthen the seedlings, and increase the temperature appropriately after planting to slow down the seedlings.

First of all, cover with mulch after sowing, and keep the temperature at 25-30°C during the day and 15-20°C at night. The seedbed temperature is preferably around 25°C. When 1/3 of the seeds have broken through the soil, the mulch film should be removed to prevent the seedlings from roasting. After the seedlings have basically emerged, the temperature should be appropriately lowered to 25-27°C during the day, 12-15°C at night, and the ground temperature is 20°C.

Secondly, after the seedlings emerge, attention should be paid to adjusting them according to growth needs to enhance the stress resistance of vegetables. Conduct low-temperature seedling hardening 5-7 days before vegetable planting, and control the seedbed temperature to 3-5°C lower than usual to enhance the stress resistance of the seedlings, improve the survival rate of the seedlings after planting, and promote seedling slowing down. However, it should be noted that when hardening seedlings at low temperature, the air temperature and ground temperature cannot be too low. Long-term low air and ground temperatures will not only fail to achieve the effect of hardening seedlings, but will affect the physiological functions of the root system and the normal progress of flower bud differentiation. Do not water the seedlings during low-temperature hardening. If the seedlings are wilting in some places at noon, water less in the wilted areas to slow down the seedlings.

Thirdly, after planting, vegetable farmers should increase the temperature appropriately in the first five days to promote the growth of the root system and facilitate seedling slowing down. For example, keep the temperature at 28-30°C during the day and 18-20°C at night. After slowing down the seedlings, the temperature can be controlled at 20-28℃ during the day and 15-18℃ at night to promote the differentiation of plant flower buds.

2. Increase the temperature appropriately during the flowering and fruit setting period.

The impact of temperature on vegetable flowering mainly lies in two aspects. One is affecting the vitality and lifespan of pollen, and the other is affecting the activity of stigmas.

Mature pollen has a certain survival time after being emitted from the anthers. At high temperatures, the metabolic activity of pollen is strong, nutrient consumption is high, and enzyme activity declines quickly, thus accelerating the aging and death of pollen. Stigma vitality is also related to whether pollen can germinate after falling on the stigma and whether pollen tubes can grow normally. The main reason for poor flowering and fruit setting of greenhouse vegetables in winter and many deformed fruits is that the temperature is too low.

Research shows that when cucumbers bloom, within a certain temperature range, the higher the temperature, the more likely it is to promote flowering and anther cracking. When the temperature in the shed reaches above 16°C, it will bloom, and the anthers will begin to crack at 16.5-17°C. , the suitable temperature is 18-21℃. If the greenhouse temperature is too high before flowering, although the anthers can crack, the flowers are only in a semi-open state; when the temperature in the greenhouse is lower than 12.8°C, the cucumber flowering and anther cracking will stop, so that pollination and fertilization cannot proceed normally. Tomatoes and other solanaceous fruits require a slightly higher temperature to bloom. The shed temperature should be controlled at 20-30°C during the day and 15-20°C at night. It is easy when the temperature in the shed is lower than 15°C or higher than 30°C. Causes the formation of misshapen flowers.

During the ripening process of solanaceous vegetables, the temperature needs to be maintained at 25-28℃ during the day, and the night temperature is about 15-18℃; while the temperature of melon vegetables during the fruiting period requires mostly 28-30℃ during the day. , the night temperature is controlled at 15-20℃. Such temperature conditions are just right for vegetable nutrients to accumulate in the fruits.

In addition to adjusting the temperature according to different crops and different growth periods, the temperature inside the greenhouse is also greatly affected by weather and seasonal changes. In the continuous rainy weather in winter, the temperature in the greenhouse is low, and without the supplement of the daytime temperature, the night temperature is too low, which often causes poor vegetable growth. In summer, when the temperature is high and the weather is fine, you need to pay attention to temperature control to avoid nutrient depletion and excessive growth caused by small temperature differences.

The soil temperature in the greenhouse during the low temperature season is very critical. It is not only the source of night temperature, but also affects the growth of the root system. Generally speaking, the soil temperature suitable for the root growth of most vegetables is around 20°C. If the soil temperature is too low, the roots will stop growing or even die, which is detrimental to cultivation. So how to manage soil temperature skillfully?

First, increase the greenhouse temperature as much as possible during the day. In the low temperature season, in order to ensure sufficient temperature at night, the daytime temperature should be appropriately increased by 2-3°C to allow more heat to be conducted into the ground and walls.

Secondly, reduce unnecessary occlusion. In the low temperature season, it is recommended to remove the old leaves covering the ground in time, and do not cultivate crops on the back wall, so as not to affect the heat storage of the back wall. It is not recommended to cover the entire shed with black mulch.

Thirdly, vegetable farmers can use straw bioreactors to increase ground temperature. After using the bioreactor in the greenhouse, the heat generated by the straw can be used to increase the ground temperature and promote the increase of air temperature. Studies have shown that compared with greenhouses without reactors, the temperature inside the greenhouse using straw bioreactors will be more than 2°C higher.