Isanti County Master Gardener
The answer to “Is it spring yet?” can be different dates. The date for the start of the astronomical spring season each year is called the Vernal Equinox, one of two days on which the overhead path of the Sun moves across the equator. The actual date depends on one’s location north or south of the equator, and will shift due to the 1/4 days by which the orbital year exceeds the calendar year.
For the Northern Hemisphere, the Vernal Equinox is the “March Equinox,” which for most of the early 21st century (2001-2006 and 2008-2017) will be March 20.
The first climatological day of spring, as mandated by the World Meteorological Organization, is March 1 every year in the northern hemisphere and Sept. 1 every year in the southern hemisphere.
Canada, the USA, and some European countries customarily observe the astronomical date (ca. March 20-21/ca. Sept. 22-23) while Australia, New Zealand, and some other European countries follow the climatological date (March 1/Sept. 1).
Customary dates are often declared “official” by the mass media although no legal basis exists for this designation. Preferences for the astronomical or climatological dates vary in other countries. Lunar dates are used across much of east Asia to determine the beginning of spring.
The ecological beginning of spring (vernal season) has no fixed dates but is marked locally by the beginning of the growing season for most plants when the local mean daily temperature reaches 6 degrees C/42 degrees F.
Many ecologists also recognize a pre-spring (prevernal) season that precedes spring.
Pre-spring is a transitional time at the end of winter when only the hardiest plants like the crocus begin to bloom.
Tropical regions of the Earth do not have a spring season. Who knew?
For more information, visit the U of M Extension website at www.extension.umn.edu or call the Isanti County Master Gardeners at 763-689-8254.
You can also visit us on Facebook: Isanti County Master Gardeners.