The world of horticulture has always been dictated by the seasons.
Seasons happen due to the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis. In temperate (such as the UK) and polar regions, the seasons are marked by changes in the amount of available sunlight which may cause animals to go into hibernation or to migrate, and plants to be dormant.
Although the astronomical dates and meteorological dates for the start of each season don't change (see table below), the behaviour of plants and wildlife and weather patterns have begun to change. Many now see this as outcome of climate change.
|Spring||21 March||1 March|
|Summer||21 June||1 June|
|Autumn||23 September||1 September|
|Winter||21 December||1 December|
The growing season — the period of time each year during which plants can grow — is an important indicator of what is happening to the world of horticulture under climate change.
The length of the thermal growing season is defined as beginning when the temperature on five consecutive days exceeds 5 °C, ending when the temperature on five consecutive days is below that threshold.
Research, looking back 233 years, has found that since 1980 the length of the growing season has been significantly changing.
According to research, Gardening in the Global Greenhouse, spring has advanced by two to six days per decade and autumn has been delayed by two days per decade.
So far researchers have found that:
By 2080 it is likely that the growing season will have increased by around 40 days.