Ask A Master Gardener – Phenology

Phenology-The Study of the Seasons

Wisconsin is blessed with four distinct seasons unlike our southern neighbors who don’t necessarily enjoy definite differences in the seasons. We see the trees bud and bloom in the spring, leaf out and grow in the summer, turn into blazes of color in the fall, and then drop their leaves during the winter.  We see the geese return in the spring to lay their eggs and raise their chicks through the summer.  When fall comes, they head south and we have a goose-less landscape for the winter.  These changes give us a front-row seat to practice phenology: the study of seasonal changes and timing. This centuries-old science is of great benefit to gardeners as well as farmers, foresters, naturalists, hunters, bird watchers, and fishermen.

The word phenology comes from the Greek word phaino meaning “to appear or to show.”  Sometimes called “the science of seasons,” phenological observations have been used for centuries to prepare for upcoming events.  Spring sets off a series of events such as tree bud break, animal emergence from hibernation, bird migration, and insect emergence.  However, phenologists are not just interested in the spring events but track the entire seasonal cycle.

Considered one of the oldest sciences, the Chinese are thought to have recorded phenological data as early as 974 B.C. The Japanese have kept records of the peak cherry blossoms since the mid-ninth century.  In Europe during the 18th century Carl Linnaeus, a Swedish botanist and the father of plant taxonomy, kept meticulous notes on 18 different locations for climate conditions and flowering times.  In England, wealthy landowner Robert Marsham, kept copious notes of phenological changes including flower blooms, insect emergence, bud burst, weather conditions, bird migration, butterfly appearance, etc.  His family continued what he began and the records span several generations, providing long-term climate records. Linnaeus and Marsham are considered to be the founders of modern phenology.

Closer to home, Aldo Leopold came to Wisconsin in 1924. From 1935–1945 he recorded volumes of seasonal events from his Sauk County home.  In 1949 his observations were published posthumously in a book, A Sand County Almanac.  His daughter Nina continued his work and went on to publish more of their work.

Many cultures use phenological indicators to predict events. Native Americans planted their corn when the oak leaves were the size of a mouse (or squirrel) ear.  While there isn’t a correlation between oak leaves, corn, and mouse ears, we now know that when the leaves reach this size, the ground has warmed enough for the corn to germinate and not rot in the soil.  Other gardening indicators include planting peas when forsythia bloom, plant potatoes when the first dandelions bloom, and plant warm season crops when lilacs bloom.

Gardening phenology indicator are not just confined to planting time. Eastern caterpillar (Malacosoma americanum) egg hatch coincides with bud break on flowering crab apple and wild plum trees.  Pay attention and proactively control them before they defoliate your trees.  When chicory starts to bloom, be vigilant for squash vine borers (Melittia cucurbitae). When Canada thistle (Cirsium arvense) is in bloom, it is time to treat for apple maggots (Rhagoletis pomonella).

Does this topic interest you? Gathering a larger body of data benefits the scientist who correlate the information as well as future generations.  If you wish to become a phenological observer, contact the Wisconsin Phenological Society or the USA National Phenology Network and contribute your observations.

Carol Shirk

Certified Master Gardener

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