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growing season,period during which plant growth takes place. In temperate climates the growing season is limited by seasonal changes in temperature and is defined as the period between the last killing frost of spring and the first killing frost of autumn, at which time annual plants die and biennials and perennials cease active growth and become dormant for the cold winter months. In tropical climates, in which there is less seasonal temperature change, the amount of available moisture often determines the periods of plant growth; in the rainy season growth is luxuriant and in the dry season many plants become dormant. In desert areas, growth is almost wholly dependent on moisture. In the Arctic the growing season is short but concentrated; the number of daylight hours is so large that the total amount of sunlight equals that of a temperate growing season with shorter days. The length of the growing season often determines which crops can be grown in a region; some require long growing seasons and others mature rapidly. Plants that are perennials in a warm climate may sometimes be grown as annuals in cooler areas; by crossing hardy plant species with less hardy but more productive types, plant breeders have developed desirable new strains that mature in a shorter period. Combinations of factors affect the growing season; in the sheltered valleys and coastal slopes of the Pacific Northwest of the United States, the heavy winter rainfall and the dry summers have produced a Mediterranean type of climate where plant growth occurs during the winter and dormancy during the summer. See climateclimate,
average condition of the atmosphere near the earth's surface over a long period of time, taking into account temperature, precipitation (see rain), humidity, wind, barometric pressure, and other phenomena.
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divisions of the year characterized by variations in the relative lengths of day and night and in the amount of heat received from the sun. These variations depend on the inclination of the equator to the plane of the ecliptic and on the revolution of the earth around
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or vegetative period.
(1) The time of year in which, according to meteorological conditions, growth and development (vegetation) of plants is possible. In temperate climates, the growing season corresponds approximately to the time interval from the last spring frosts to the first autumn frosts (the frost-free period); in tropical and sometimes in subtropical climates, the growing season lasts the year round. Duration of the growing season in considerable measure determines the composition of local wild and cultivated vegetation.
(2) The time necessary for a plant to go through a complete cycle of development; in agricultural practice, the period from the beginning of growth to the gathering of the harvest. In the same agricultural crop, varieties may be distinguished with short growing seasons—that is, early ripening—and with long ones—late ripening. The former are cultivated in more northerly regions with short frost-free periods or in arid regions, so that they may ripen before drought; the latter are cultivated in more southerly regions. The dependence of the duration of the growing season on conditions of the environment, especially on temperature and light, is quite complex.
The growing seasons of the most important plants under the conditions of central and southern USSR are 270-360 days for winter rye, 200-350 days for winter wheat, 62-189 days for spring wheat, 130-150 days for corn, 101-168 days for sunflowers, 162-264 days for cotton, and 150-210 days for sugar beets. The growing season is determined by the total quantity of heat obtained by the plant in the course of its period of development; the quantity of heat is expressed by a number obtained by multiplying the number of days of the growing season by the average daily temperature.
REFERENCESMaksimov, N. A. Kratkii kurs fiziologii rastenii, 9th ed. Moscow, 1958.
Chailakhian, M. Kh. Osnovnye zakonomernosti ontogeneza vysshikh rastenii. Moscow, 1958.
Sabinin, D. A. Fiziologiia razvitiia rastenii. Moscow, 1963.
Genkel’, P. A. Fiziologiia rastenii s osnovami mikrobiologii, 3rd ed. Moscow, 1965.
N. A. MAKSIMOV