Growing season

A growing season is a specific part of the year. It is defined by local environmental conditions that permit normal plant growth. These conditions include temperature, rainfall, and the amount of daylight available. While every individual plant has a unique growing season based on its genetic adaptation, most can be grouped into macro-environmental classes. The axial tilt of the Earth is a primary reason why growing seasons vary across the globe.

Geography dictates the length and timing of these seasons through several mechanisms. Latitude is one of the most significant factors. As you move further from the equator, the angle of the Sun in the sky becomes lower. This lower angle means sunlight is less direct. Consequently, the soil takes a longer time to warm up during the spring months. This delay causes the growing season to begin later in northern regions. Altitude also plays a role in this process. High elevations have cooler temperatures, which shortens the growing season compared to low-lying areas at the same latitude.

In North America, the growing season changes drastically based on latitude. The continental United States stretches from 25° north to 49° north. North of the 45th parallel, the growing season is generally only four to five months long. This period typically begins in late April or early May and ends in late September or early October. These areas experience warm summers and cold winters with heavy snow. In contrast, many areas south of the 30th parallel have year-round growing seasons. These regions feature hot summers and mild winters. Farmers in these southern areas can plant cool season crops, like peas and spinach, in the fall or late winter. They plant warm season crops, such as corn and beans, in the late winter or early spring.

Extreme environments in North America create unique growing patterns. In the desert Southwest, the growing season effectively runs during the winter. It lasts from October to April. This happens because the summer months are too hot and arid for most plants. These extreme conditions are inhospitable to anything not specifically adapted to the desert. Some crops, such as melons and tomatoes, originated in tropical or subtropical regions. These plants require hot weather and a growing season of at least eight months. In colder climates, gardeners often start these plants in a greenhouse. They then transplant them outside during the late spring or early summer.

Europe is also divided by distinct geographic features and seasonal patterns. The Pyrenees, Alps, and Southern Carpathians mountain ranges divide the continent into two main regions. Southern Europe and the Mediterranean are mostly south of the 45th parallel. In these areas, growing seasons last six months or more. The climate features hot summers and milder winters. Precipitation in these regions falls mainly between October and March, leaving summers dry. In the extreme south of Europe, the growing season can last all year. Because of the warm winters, vegetation on Mediterranean islands is often evergreen.

Northern and Central Europe extend north from the 45th parallel toward the Arctic Circle. The growing seasons here are much shorter due to the lower angle of the Sun. These seasons generally range from five months down to only three months in the highlands of Russia and Scandinavia. Along the Atlantic coast, the climate is moderated by humid ocean air. This makes winters relatively mild, and snow or freezing weather is rare. However, because summers are also mild, heat-loving plants like maize do not usually grow in Northwestern Europe. Further inland, the winters become much colder. Even in the north, the extreme length of summer daylight can help. In Scandinavia, days can last 17 hours or more, allowing plants to achieve significant growth.

In tropical and desert climates, water availability becomes the primary limiting factor. In tropical savanna, hot semi-arid, hot desert, or Mediterranean climates, the growing season is often limited by dry periods. In cooler climates, snow or frozen soil can stop growth. In hot climates, however, people can use irrigation to extend the growing season. Irrigation is the process of bringing water to land to help plants grow. This can allow for year-round growth even in areas that would otherwise only support xerophytic plants. In tropical regions, the growing season can also be interrupted by a rainy season. For example, coffee is grown in Indonesia, but the rainy season interrupts the growth of the coffee beans. In Colombia, coffee can be harvested year-round because they do not experience a rainy season.