Growing season

The continental United States ranges from 49° north at the US-Canadian border to 25° north at the southern tip of the US-Mexican border. Most populated areas of Canada are below the 55th parallel. North of the 45th parallel, the growing season is generally 4–5 months, beginning in late April or early May and continuing to late September-early October, and is characterized by warm summers and cold winters with heavy snow. South of the 30th parallel, the growing season is year-round in many areas with hot summers and mild winters. Cool season crops such as peas, lettuce, and spinach are planted in fall or late winter, while warm season crops such as beans and corn are planted in late winter to early spring. In the desert Southwest, the growing season effectively runs in winter, from October to April as the summer months are characterized by extreme heat and arid conditions, making it inhospitable for plants not adapted to this environment.

Certain crops such as tomatoes and melons originated in subtropical or tropical regions. Consequently, they require hot weather and a growing season of eight months or more. In colder climate areas where they cannot be directly sowed in the ground, these plants are usually started indoors in a greenhouse and transplanted outside in late spring or early summer.

The Pyrenees, Alps, and Southern Carpathians effectively divide Europe into two regions. Southern Europe and the Mediterranean are in general south of the 45th parallel. The growing seasons last six months or more, and the climate is characterized by hot summers and milder winters. Precipitation mainly falls between October and March, while summers are dry. In the extreme south of Europe, the growing season can be year-round. Vegetation on the Mediterranean islands is often evergreen because of the relatively warm winters.

Northern and Central Europe extend north from the 45th parallel past the Arctic Circle. The growing seasons are shorter because of the lower angle of the Sun and generally range from five months to as little as three in the highlands of Scandinavia and Russia. Climate on the Atlantic coast is considerably moderated by humid ocean air, which makes winters comparatively mild, and freezing weather or snow are rare. Because summers are also mild, many heat-loving plants such as maize do not typically grow in Northwestern Europe. Further inland, winters become considerably colder. Despite the short growing season in parts of Scandinavia and northern Russia, the extreme length of daylight during summer (17 hours or more) allows plants to put on significant growth.

In some warm climates, such as the tropical savanna climates (Aw), the hot semi-arid climates (BSh), the hot desert climates (BWh) or the Mediterranean climates (Cs), the growing season is limited by the availability of water, with little growth in the dry season. Unlike in cooler climates where snow or soil freezing is a generally insurmountable obstacle to plant growth, it is often possible to greatly extend the growing season in hot climates by irrigation using water from cooler and/or wetter regions. This can in fact go so far as to allow year-round growth in areas that without irrigation could only support xerophytic plants.

In the tropical regions, the growing season can be interrupted by periods of heavy rainfall, called the rainy season. For example, in Colombia, where coffee is grown and can be harvested year-round, they don’t see a rainy season. However, in Indonesia, another large coffee-producing area, they experience this rainy season and the growth of the coffee beans is interrupted.[3]