What are the temperature requirements for grapes?

The traditional grape protected cultivation is mainly to promote cultivation, so that grapes can be put on the market early, meet the low season of grape supply in early spring and pursue higher economic benefits. Therefore, one of the important measures to control the environment of protected cultivation is to increase the temperature. Proper warming measures are beneficial to plant growth, otherwise, it will be harmful to grapes. The cultivated species of Vitis originated from temperate zone and subtropical zone, belonging to temperate fruit trees. Temperature affects the whole process of grape growth and development, and directly determines the yield and quality.

the response of grapes to low temperature varies with species and varieties. During the winter dormancy period, the full buds of Eurasian population varieties can tolerate the low temperature of-2 ~-18℃ for a short time, the fully full one-year branches can tolerate the low temperature of -22℃ for a short time, and the perennial vines will be frozen at around -2℃. The root system of grape is not tolerant to low temperature, and the root system of Eurasian population will be frozen at -4℃ and freeze to death at -6℃ for about two days. The roots of some varieties of European and American hybrids are damaged by freezing at-7 ~-6℃ and can freeze to death at-1 ~-9℃. Therefore, when cultivating grapes in the north, special attention should be paid to the overwintering protection of branches and roots. Although the absolute low temperature in some places is not lower than -17℃ in winter, there are many fruit branches in buried plants, so burying the soil for wintering is often regarded as one of the high-yield measures. However, in some years, although the plants are buried in the soil, the roots are still frozen, and there is often a problem that young plants still die after being buried in the soil for the winter, mainly because the roots are frozen to death due to insufficient buried soil thickness. Weak trees and weak plants often lead to low cold resistance of plants.

grapes have different requirements for temperature in different growth stages.

(1) dormant period

When the average daily air temperature drops below 8℃ in autumn, the leaves gradually wither and fall off, and the plants enter dormant period. In spring, when the soil temperature is 7 ~ 1℃, the roots begin to move. Generally, in early spring, when the air temperature is stable above 1℃, the grapes begin to sprout.

It is generally believed that the absolute lowest temperature isotherm of -17℃ in winter and the altitude of 7 meters above sea level are the dividing lines between burying grapes in winter and not burying them in winter and overwintering in the open field. The area with an altitude of 6 ~ 7 meters and the absolute lowest temperature of-17 ~-1℃ in winter is a cold-proof area that can be buried or not; In case of extreme weather, or long low temperature, or accompanied by drought and windy in winter, vineyards often suffer from freezing damage. Therefore, it is suggested that the technical measures of burying soil for cold protection should be taken in winter in areas where it is theoretically possible to bury soil for cold protection in the open field. Although grapes planted in protected facilities do not adopt the measures of burying the soil to prevent cold, the temperature is adjusted by covering with greenhouse film and thermal insulation quilt, and the air temperature should be kept at-5. ~ 7.2℃ for a period of time in winter, so that the grapes can pass dormancy.

protected grape cultivation needs 8 ~ 12 hours at ~ 7.2℃ to pass natural dormancy, and the fruit will be guaranteed in the next year. Therefore, grapes cultivated in protected facilities must meet their low temperature requirements before warming up. In actual production, it is often in mid-November, and the straw curtain is covered with film during the day and the vent is closed; At night, the straw curtain is uncovered and the vent is opened, so that the temperature in the greenhouse can be reduced to below 7.2℃ and above -5℃. This not only increases the low temperature, but also protects the grape plants from freezing injury. After meeting the cold demand, the winter buds of fruiting mother branches were coated with 2% lime nitrogen in mid-December to promote them to break dormancy.

(2) Germination to flowering

This period is mainly vegetative growth, and the lowest temperature should be 5 ~ 6℃ and the highest temperature is 28℃. Under normal circumstances, it should be kept at about 2℃ during the day and 1 ~ 15℃ at night, so that the growth of new shoots and flower bud differentiation are accelerated; If the temperature is too high and the temperature rises too fast during this period, the flower organs will differentiate and develop too fast, resulting in abnormal and abnormal development, which will hinder the development of flower organs and reduce the fruit-setting ability.

(3) From flowering to berry harvest

Before and after flowering, it should be kept at 2 ~ 28℃ during the day and 16 ~ 18℃ at night, with the lowest temperature not lower than 15℃. Keep 25 ~ 28℃ during the day and 18 ~ 2℃ at night during the young fruit period; The minimum is not lower than 15℃, but it should not exceed 2℃. When the lowest outside temperature stably passes through 1℃, the film cover can be removed and turned into the open field form.

The fruit quality can be excellent only when the temperature difference between day and night is more than 1℃, when it is 28 ~ 3℃ in the daytime and 16 ~ 18℃ at night. The small temperature difference between day and night is not conducive to the accumulation of nutrients. The maturity and sugar content of berries are closely related to the effective accumulated temperature. Insufficient effective accumulated temperature, low sugar content, high acid content, color difference and poor quality of berries.