Growing season

The growing season is the part of the year during which local weather conditions (i.e. rainfall and temperature) permit normal plant growth. While each plant or crop has a specific growing season that depends on its genetic adaptation, growing seasons can generally be grouped into macro-environmental classes.

Geographic conditions have major impacts on the growing season for any given area. The elevation, or the height above sea level, and temperature of a region are two of the main factors that affect the growing season. Generally speaking, the distance a location is from the equator can be a strong indicator as to what the growing season will look like, however in a high elevation area, regardless of proximity to the equator, a shorter growing season will generally be experienced. Proximity to the ocean also can create less extreme conditions, especially in terms of temperature, which has the potential to extend the growing season further in either direction. In hotter climates, particularly in deserts, despite the geographic barrier of limited water sources, people have been able to extend their growing season in these regions by way of diverting water from other areas and using it in their agriculture. The ability to use these irrigation methods, despite geographic challenges, has made it possible to enjoy almost a year-round growing season.

In agriculture, season extension is anything that allows a crop to be cultivated beyond its normal outdoor growing season. Examples include greenhouses, polytunnels, row cover, and cloches.

In the United States and Canada, the growing season usually refers to the time between two dates: 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 last date at which the overnight low temperature drops below 0 °C (32 °F) in the spring and the average date at which the overnight low first drops down below 0 °C (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.

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