The Earth’s Seasons

As a gardener it makes common sense to set my gardening clock by the natural rhythms or seasons of the land I live on. Some rhythms are global, affecting our whole planet, some are regional affecting perhaps a whole country, some are local affecting a smaller area still and some are more specific yet and relate to the many micro-climates in which a single plant may exist. In order to understand the smaller rhythms it is first important to understand the broader rhythms or seasons that affect our whole planet.

The Earth’s seasons are brought about by the fact that the earth orbits the sun on a tilted axis. The Earth’s axis is tilted at an angle of approximately 23.44° from the orbital plane. For us this means that for half of the year from the Spring or March Equinox (around March 20th) to the Autumn or September Equinox (usually September 22nd or 23rd) the northern hemisphere tips toward the Sun, becoming closest to the sun at midsummer, Summer or June Solstice (usually June 21st) when we experience the longest days and most amount of sunlight. For the other half of the year the Southern Hemisphere follows the same pattern while we in the Northern Hemisphere travel away from the sun becoming furthest away at Midwinter, Winter or December Solstice (usually December 21st or 22nd) when we experience the shortest days and least amount of sunlight.

The two points in the year when the Sun is directly overhead at the equator are the equinoxes when the light of day and dark of night are of equal measure. Around the equinoxes sunrise and sunset at about the same time AM and PM.  From this point sunrise gets later and sunset gets earlier by a few minutes each day until the low point of the Winter Solstice when we experience the shortest day of the year. The decline of daylight hours reverses and the days start to lengthen again until we again have equal day and night at Spring Equinox and the days continue to lengthen until the Summer Solstice.

 What this means to gardeners

Many plants are set into growth not only by temperatures or rainfall but by the amount of available sunlight, so understanding how the length of the day changes through the year is important. Many cultures celebrated or marked their years by the Solstices and Equinoxes in the past. Vestiges of these times, when calendars and events were influenced more by the natural rhythms of the earth than man-made simplified calendars, still exist. In England, for example, Harvest Festival is still celebrated on the Sunday of the full moon closest to the September or Autumn equinox. For gardeners we still have reason to mark their passing as they tell us the changing points of the lengthening and shortening of daylight hours.  There are many old gardening wisdoms of when or what to sow or harvest by these seasonal markers. It is something I am keen to learn more about but so far I’ve found reference to only a few.

Spring Equinox

is the time for many gardeners to start sowing and planting the new seasons crops, as the amount of daylight becomes greater than the amount of darkness. In France, it is tradition to sow French beans undercover around this date.

Summer Solstice

The longest day of the year. Many asparagus growers claim Asparagus should not be cut after the summer solstice. It is also said to be point at which alliums should be harvested.

Autumn Equinox

This is the traditional period of harvesting crops grown in the warmer months for storage into the colder months.

Winter Solstice

The Shortest day of the year. It is a French tradition to sow shallot seeds on the shortest day of the year and harvest them on the longest.

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