What temperature is needed to grow vegetables?

Among the environmental conditions that affect the growth and development of vegetables, temperature is the most sensitive. All kinds of vegetables have three basic points of their growth and development temperature: the lowest temperature, the optimal temperature and the highest temperature. In production, the organ formation of various vegetable products should be arranged in the most suitable month of local climate in order to achieve the goal of high yield and high quality.

First, the classification requirements of vegetable temperature

According to the different requirements of various vegetables for temperature conditions and the temperature they can tolerate, vegetable plants can be divided into five categories, which is an important basis for arranging vegetable cultivation seasons.

1, cold-resistant perennial vegetables: including leek, day lily, asparagus, etc. In the growing season, the aboveground part can withstand high temperature and die in winter. It overwinters with underground perennial roots (stems) and can withstand low temperature of-10℃.

2. Cold-tolerant vegetables: including spinach, parsley, green onions, onions, garlic and so on. It grows best at 15~20℃ and can tolerate the low temperature of-1~-2℃.

3. Semi-cold-tolerant vegetables: including Chinese cabbage, Chinese cabbage, radish, carrot, cabbage, peas, broad beans and so on. It grows best at 17~20℃ and can tolerate short-term low temperature of-1~-3℃.

4. Warm-loving vegetables: including cucumbers, tomatoes, peppers, kidney beans and eggplant. , suitable for growth at 20~30℃, frost-resistant, easy to drop flowers below 15℃, and poor growth results above 35℃.

5. Heat-resistant vegetables: including wax gourd, pumpkin, watermelon, cowpea, sword bean, amaranth and water spinach. It grows well around 30℃, and can still grow normally at 35~40℃.

Vegetables that like temperature and heat resistance must be cultivated in protected areas such as greenhouses in winter. Cold-tolerant or semi-cold-tolerant vegetables are required to be cultivated in summer and early autumn, and shading and covering measures or off-season cultivation in high mountains are adopted.

Second, the temperature cycle and vegetable production

The response of vegetable crop growth and development to the periodic change of day and night temperature is called vegetable temperature cycle. Vegetable crops need higher temperature during the day, which is beneficial to photosynthesis, while lower temperature at night can reduce the consumption of stored substances and is beneficial to the transportation and storage of assimilates.

There is a certain temperature difference between day and night, and the temperature at night should not be too low, because vegetable crops still grow at night and constantly absorb water and nutrients. Therefore, attention should be paid to the day and night temperature management of protected cultivation. The temperature difference between day and night is larger on sunny days and smaller on cloudy days.

Temperature cycle is of great significance to guide vegetable cultivation. For example, when determining the sowing season, the formation time of product organs is arranged in a period with large temperature difference between day and night, which is beneficial to the accumulation of nutrients and the expansion of product organs. Another example is to promote and control the growth of seedlings and cultivate strong seedlings through the management of daily temperature and night temperature in different periods. When cultivated in protected fields, the daytime temperature and night temperature are often adjusted in several sections according to cloudy weather. For example, the temperature in sunny day is 2~5℃ higher than that in cloudy day, 65,438+0 ~ 4℃ higher than that in cloudy day at night, 2~5℃ lower than that before noon in the afternoon, and the temperature is higher after sunset for nutrient operation, and then the temperature continues to decrease, so as to keep the nutrient consumption at a minimum.

Thirdly, the influence of soil temperature on vegetable growth.

In a certain range, the soil temperature rises and the growth is accelerated. The optimum temperature for root absorption of various vegetables is different. The root growth of warm-loving vegetables needs high soil temperature, and the suitable temperature for root elongation and penetration into soil is 18~20℃. The roots of cucumber and sweet pepper are very sensitive to low temperature.

Watering in winter and spring should be controlled in vegetable production to prevent the decrease of ground temperature from affecting the growth and absorption of roots. Measures such as intertillage loosening soil or plastic film mulching can increase ground temperature and conserve moisture. Soilless cultivation of warm-loving vegetables in winter and spring often leads to poor growth due to low water temperature, so increasing the temperature of nutrient solution can not be ignored. If the soil temperature is too high, it will also affect growth. When the soil temperature exceeds 25℃, the absorption capacity of roots will also weaken. When the soil temperature is above 30~35℃, the root growth will be inhibited, which will easily lead to plant disease and premature aging. In summer, small irrigation, soil tillage and border mulching are used to reduce ground temperature and protect roots. In addition, it is not allowed to water suddenly at noon in the summer when the growth is vigorous, so that the rhizosphere temperature suddenly drops and the plants wither or even die.

Fourth, the harm of high temperature and low temperature to the growth and development of vegetables

High temperature hazard

1, high temperature accompanied by strong light causes plants to lose water and wilt, which affects their growth. Failure to keep up with water may lead to plant death.

2. High temperature affects the pollen vitality, which leads to the flowering of solanaceous fruits and leguminous vegetables, the fruit setting rate decreases and the abnormal fruits increase.

3, high temperature and strong light are easy to burn tomatoes, watermelons, wax gourd and peppers.

4. High temperature and strong light will weaken photosynthesis and enhance respiration, resulting in insufficient nutrients in the body and poor growth.

5. Affect flower bud differentiation and sex differentiation: High temperature and long sunshine often make cucumber male flowers increase and female flowers differentiate late. When tomato and pepper flower buds differentiate, there are few flowers and poor development at high temperature.

6, affect the normal pigment formation, tomato at high temperature (above 35℃), lycopene is difficult to form normally, so the fruit often appears yellow, red and white variegated, which greatly reduces the commodity value.

Heat-resistant varieties should be selected first in high-temperature cultivation. In addition, watering, puddle cultivation, sunshade net covering or ground covering can be used to cool down in the morning and evening during the high temperature period. In winter and spring, small arch shed and greenhouse cultivation should pay attention to ventilation and cooling in sunny days to avoid high temperature injury.

(2) Low temperature hazards

Low temperature injury can be divided into cold injury and freezing injury. Freezing injury, also known as chilling injury, refers to the damage to vegetables at a low temperature above 0℃; Freezing injury refers to the phenomenon that vegetables freeze in the body at a low temperature below 0℃.

1. Eggplant vegetables, melons and beans encounter low temperature, which often leads to flower dropping, affecting pollen vitality, or even no pollen, affecting fruit setting rate and producing deformed fruits.

2. Low temperature often makes biennial vegetables (such as Chinese cabbage, cabbage and root vegetables) bolting before or during the formation of product organs, that is, bolting in advance.

Freezing injury below 3.0℃ often causes tissue damage, dehydration and drying, leading to plant death.

4. Low temperature hinders the normal growth of vegetables, affects the water absorption of roots, leads to unbalanced water supply, and plants may wilt, inhibit the formation of chlorophyll, resulting in yellow or yellow-white leaves, which is a typical symptom of chilling injury of warm-loving vegetables.

Sowing warm vegetables in early spring often leads to seed rot. In low temperature and rainy weather, the leaves of seedlings gradually turn yellow, the roots are rusty brown, the lateral roots and root hairs die, and the aboveground parts wilt, commonly known as "retting roots and dropping seedlings".

We can choose varieties with strong cold resistance for cultivation, temper seedlings at low temperature, apply phosphorus and potassium fertilizer to prevent overgrowth, improve the quality of seedlings or plants, and improve the humidity of air near the ground by irrigation or foliar spraying to reduce freezing injury. The most effective way can be to use plastic film mulching cultivation measures or smoking, geothermal heating and other measures to prevent low temperature injury.

Five, low temperature vernalization and vegetable production

Biennial vegetables (such as Chinese cabbage, cabbage, celery, spinach, radish, etc. ) all need certain low temperature conditions to bolting and flowering. This physiological process that requires a low temperature before bolting and flowering is called "vernalization phenomenon" or "vernalization stage" Bolting and flowering under long sunshine and high temperature after vernalization. The conditions required for two-year-old vegetables to pass vernalization stage vary with different types of vegetables, which can be basically divided into two categories.

1. Seed vernalization vegetables: such as Chinese cabbage, radish, mustard, spinach, lettuce, etc. They can spend the vernalization stage at any time since the seed germination, as long as there is a suitable low temperature for a certain period, and then bolting and flowering after a long period of sunshine and high temperature. The vernalization temperature of most vegetables is 0~ 10℃, preferably 2~5℃. The vernalization temperature of some vegetable species or varieties can be stabilized at 15℃ or higher, and the duration of low temperature is 10~30 days. This kind of vegetables need a wide temperature range and a short time to pass the vernalization stage, so it is easy to encounter such a situation in production. Therefore, due to improper variety selection and sowing date, it is easier to bolting and blossom before or during the formation of product organs. This phenomenon is called "early bolting" or "immature bolting". For example, Chinese cabbage in spring should be "Yangchun" and "Chundajiang" varieties. The vernalization stage needs low temperature and lasts for a long time, so it is not easy to get lucky in advance. Chinese cabbage is sown in spring, so it should be raised with hot silk to avoid bolting caused by low temperature at seedling stage. In addition, the sowing date should not be too early, and plastic film should be used for cultivation. The selection of sowing date is very important for off-season cultivation of alpine Chinese cabbage. For example, sowing "xia yang" Chinese cabbage in high mountains (about 800 meters above sea level) in early April can easily lead to bolting and flowering without heading.

2. Green (seedling) vernalization vegetables: such as cabbage, onion and celery. Only when the seedlings grow to a certain size and go through the vernalization stage can they feel the influence of low temperature. Low temperature has little effect on germination seeds and too small seedlings of these vegetables.

Plants of a certain size are usually represented by the number of leaves, stem diameter and other indicators. For example, early-maturing Chinese cabbage is weak in winter, and the diameter of seedlings is above 0.6 cm. It can be vernalized at 10~ 15℃ for more than 30 days. Early sowing of spring cabbage is easy to bolting, and the sowing date should be postponed appropriately. The winterness of mid-mature varieties is between early maturity and late maturity, the stem diameter is generally above 65438±0cm, and vernalization can only be completed at a low temperature of 40-60 days. When spring cabbage is cultivated, the sowing date is between early maturity and late maturity, and the variety belonging to this type is "Jingfeng 1". Late-maturing varieties are strong in winter. The stem diameter of general plants is above 1.3 cm, and vernalization can only be completed after 70 days of low temperature. When cultivated as spring cabbage, the sowing date can be advanced appropriately. Therefore, spring cabbage cultivation should choose varieties that are not easy to bolting in advance.

Different varieties have different requirements on seedling age, low temperature degree and low temperature duration when they go through vernalization stage. Varieties with low temperature requirements are called weak winter varieties, and those with strict requirements in vernalization stage are called strong winter varieties. When cultivated as a commercial vegetable in spring, it is advisable to choose a variety with strong winterness and arrange a suitable sowing date to avoid premature bolting due to long-term low temperature when the seedling growth reaches the vernalization size requirement.