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The growing season is a term used for the period of time in a given year when the climate is prime for both indigenous and cultivated plants to experience the most growth. This period is observed in botanical, horticultural, and agricultural settings. The growing season of a given area can be affected by its relative distance from the equator, as well as elevation.〔(【引用サイトリンク】url=http://education.nationalgeographic.com/education/encyclopedia/growing-season/?ar_a=1 )〕 Growing seasons are measured in two ways; the first being the number of consecutive frost-free days. This can be found by looking at the average last frost day of the Spring for a given area, and then looking at the average first hard frost date in the fall or winter. The second way of measuring the growing season is by looking at the number of days in the year when the average temperature is above the point at which a crop will germinate. This method of measurement is affected by which crop you are intending on growing, so it varies considerably. For example, wheat will germinate at temperatures above 40° F, while corn will only germinate at temperatures above 50° F.〔 ==North America== In the United States and Canada, the growing season usually refers to time between the last frost in the spring and the first hard frost in the fall. Specifically, it is defined as the period of time between the average date at which the overnight low temperature last drops below 32° F in the spring and the average date at which the overnight low first drops down below 32° F in the fall. These average last and first frost dates have reportedly been occurring earlier and later, respectively, at a steady rate, as observed over the last 30 years. As a result, the overall observed length of the growing season in the United States has increased by about two weeks in the last 30 years. In the cooler areas of North America, specifically the Northern regions of the United States and Canada, the growing season is observed between around April or May through October. This period is longer in the southern regions of the United States, where the growing season can start as early as February or March and continue all the way through November or December. These rough timetables vary significantly by areas that are in higher elevations and also closer proximity to the ocean. Because of relatively long growth requirements of several crops grown in the United States, growing season extension practices are commonly used as well. These include various types of row covering techniques such as using cold frames and garden fabric over crops. Greenhouses are also a common season extension practice, particularly in higher elevation regions that only enjoy 90 day growing seasons. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「growing season」の詳細全文を読む スポンサード リンク
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