Greenhouses, whether they are ordinary small ones at home or professional ones like the "Chengfei Greenhouse", temperature control is of crucial importance for the healthy growth of plants. Understanding the "overheating" threshold, as well as the harms, causes and solutions related to it, is a must for every grower.
1、The "Overheating" Threshold of Greenhouses
All kinds of greenhouses, including the "Chengfei Greenhouse", have a clear "overheating" standard. Generally, when the temperature exceeds 90 degrees Fahrenheit, it enters the overheating range. Heat-tolerant vegetables such as tomatoes, okra and eggplants can grow normally between 80 and 90 degrees Fahrenheit. However, once the temperature exceeds 90 degrees Fahrenheit, problems like yellowing leaves, slowed growth of new branches, deformed fruits and reduced fruit-setting rate will appear in tomatoes. For cool-loving vegetables such as arugula, beets and broccoli, when the temperature exceeds 85 degrees Fahrenheit, they will be affected. Arugula will have wilted leaves, slower growth and is more likely to be attacked by pests and diseases, resulting in reduced yields.
2、The Harms of High Temperatures to Greenhouse Plants
High temperatures cause multiple harms to greenhouse plants. In terms of plant physiological processes, take watermelons for example. High temperatures disrupt photosynthesis and respiration, leading to the inhibition of the activity of key enzymes, a decrease in the efficiency of carbon dioxide fixation, and an abnormal increase in respiration consumption. As a result, the quality of fruits deteriorates due to nutrient imbalance, and problems like "crystal melons" appear, with declined taste and nutritional value.
From the perspective of plant resistance, when greenhouse cucumbers are exposed to high temperatures with poor ventilation, the cuticle and wax that protect the plants from diseases are damaged, and the synthesis of disease-resistant substances is blocked. Then, powdery mildew fungi take the opportunity to invade, causing diseases in leaves and stems, restricting photosynthesis, resulting in weak vines, deformed cucumbers and greatly reduced yields.
Moreover, high temperatures disrupt the growth rhythm of plants, causing leafy vegetables such as bok choy and lettuce to bolt and flower prematurely. The nutrients in the leaves are transferred, making them smaller and harder, with worse taste and reduced yields.
3、What Causes Greenhouses to Overheat?
The overheating of greenhouses is mainly caused by geographical location and seasonal factors. In hot climate regions such as the southern and southwestern parts of the United States, Mexico, India and the Philippines, due to their location in tropical and subtropical areas with strong sunlight and long periods of high temperatures, greenhouses absorb a lot of heat and have difficulty in dissipating it. Even with conventional cooling measures, the temperature is still likely to exceed the standard. In contrast, in cold regions like Alaska, greenhouses focus on heat preservation, which is quite different from the problems in hot regions.
As for the season, summer is the "high temperature disaster" for greenhouses. At this time, the direct sunlight point shifts, the length of daylight increases and the intensity of sunlight becomes stronger. For example, in North China, the daylight in summer can reach 14 to 15 hours. The greenhouse roofs receive a lot of heat, and the heat accumulates. The temperature rises from morning to night and is hard to dissipate at night, leaving plants in a difficult situation of high temperatures.
4、Solutions to Cool Down Greenhouses
There are practical ways to cool down greenhouses. In terms of shading for cooling, farmers in Jiangsu and Zhejiang regions will set up black shade nets at 10:30 am during the high temperature period from July to August, leaving an interval of about 20 centimeters between the shade nets and the greenhouse film to form a ventilation zone. This effectively reduces direct sunlight and disperses heat, lowering the temperature in the greenhouse by 5 to 8 degrees Fahrenheit, helping tomatoes, peppers and other crops to resume good growth. Even the "Chengfei Greenhouse" has adopted similar operation concepts, precisely adjusting the shading facilities to assist in the regulation of internal temperature and humidity and ensure the healthy growth of plants.
Ventilation is also crucial, which is like injecting vitality into the greenhouse. In a flower greenhouse in the suburbs of Beijing, gardeners open the top and side vents every day when the temperature just starts to rise. Hot air is discharged, and fresh air with carbon dioxide flows in, improving the temperature and humidity. Lilies in a good environment will have large, brightly colored flowers and a longer flowering period, while those in poorly ventilated areas will be weak and wither easily.
Spraying for cooling is also effective. When farmers grow grapes in southern fruit greenhouses, they spray water at the right time. The evaporation of water absorbs heat and lowers the temperature. However, the amount of spraying needs to be carefully controlled. Excessive spraying will cause the humidity to soar above 90%, leading to mildew and rot of grape clusters. Reasonable operation can create a suitable temperature and humidity environment to ensure the healthy growth of grapes.
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●#Greenhouse Thermoregulation
●#High Temp Defense
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●#Regional Greenhouse Temps
Post time: Jan-18-2025
