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The calendar indicates
spring begins on the vernal equinox, March 20. However this year in my garden
south of Madison, signs of spring began to appear as early as the last week in
February when my crocuses, winter aconites, and snowdrops reached early bloom.
In Wisconsin there is no such thing as a "normal" weather year. In the
35 years I’ve lived in this state, I’ve experienced extremes during at least
one season out of every year. It is for this reason that the solar calendar is
often not the most accurate indicator of natural events.
Because many factors such as latitude, altitude, and the buffering effects of large bodies of water affect climatic conditions, regional differences occur in all biological events. Because of the wide range of variability in climate, scientists look elsewhere to predict natural events. This area of science is called phenology.
Phenology is an area of
science that has received a renewed interest in recent years. It can be defined
as the timing of natural living processes with weather events. The return of
various migratory songbirds, the blooming of wildflowers and woody landscape
plants, and the development of locally indigenous insects are all examples of
phenological events which are easily observed each spring in any location.
Phenology observes the relationship between 1) discrete phenological events, 2)
events and the season, 3) events and local weather conditions, and 4) events and
climatic changes. Records of such natural events over a period of several years
are helpful in determining climatic changes as well as any shifts in native
plant or animal populations.
Historically, phenology received much more attention than it has in recent history. Until the early 1900's phenology was frequently used to predict when certain life events were expected to occur. The father of plant taxonomy, Carl Linnaeus, was one of the first people to begin recording phenological observations. On a more local scale, in Wisconsin, Increase A. Lapham and Aldo Leopold kept detailed records of natural events.
In 1959, a number of people with a common interest in phenology met in Madison to discuss ways of systematically collecting phenological data. It was from this interest that the Wisconsin Phenological Society was born. The first meeting of this new society was held in January 1961. The initial response to the membership drive was outstanding. During the early years, membership was consistently above 500. Some of the early activities of the Wisconsin Phenological Society include the observation of phenological events on the common lilac, emergence of Promethia moths, and the freezing and thawing dates of Wisconsin lakes. On a larger scale, Wisconsin phenological observers participated in the lilac plant survey in the northeastern United States.
Phenology is not the same as folk
forecasts such as whether Punxsutawney Phil will see his shadow and burden us
with six more weeks of winter. Or whether woolly bear caterpillars can predict
the severity of the upcoming winter by the ratio of brown to black coloration.
Some of the important things
gardening phenologists keep track of are the dates of the first and last frosts,
when the ground freezes and thaws, the best time to hunt morel mushrooms, the
planting and blooming of herbaceous and woody landscape plants and the emergence
of insect pests. I’m sure you’ve heard the saying "plant corn when oak
leaves are the size of a squirrel’s ear". We all know that planting corn
has nothing to do with oak leaves or squirrel’s ears but over time, farmers
have learned that when oak leaves have reached this size, the soil is warm
enough for corn seed to germinate without rotting in the soil. This holds true
for all warm-season annual plants.
Crabgrass, the bane of most
gardeners, germinates when the soil temperature at 4" stabilizes at 55°F.
Although it is difficult to correlate soil activities with ambient temperature,
this soil temperature correlates roughly with when the forsythia is in bloom. This is important to know if you plan to apply an herbicide
to prevent crabgrass seed from germinating. Too early or late an application
will miss the window of opportunity and you’re left with only mechanical tools
(cultivation) with which to control this weed.
In years such as this year, weather patterns put spring into a state of suspended animation. Spring-flowering bulbs put on a spectacular show for weeks. In contrast, the spring of 1994 was non-existent with bulbs and wildflowers rushing through bloom because of the unusual, warmer than normal temperatures. This trend continued through the record heat of the summer causing many garden plants to suffer from something we don’t often see in Wisconsin - heat stress.
Another area where phenology is
useful in gardening is in the prediction of insect pest problems. Because
insects are cold-blooded, their growth and development is directly correlated
with weather conditions, particularly temperature. Plant-feeding insects have
evolved closely with their host plants and therefore there is a similar
developmental period between the two. By monitoring plant development, which is
characterized by distinct life stages, you can also monitor insect development.
For example, Eastern tent caterpillar egg hatch coincides with budbreak on
flowering crabapple and wild plum - their most common host plants. Looking for,
and controlling tent caterpillars at this early stage is much more successful
than waiting until they have defoliated your plant.
Allergy sufferers will also find
phenology useful. Allergies to plant pollen are often seasonal. Exact times of
allergic reactions will vary depending on the weather and the rate of
development of the offending plant. Trees typically pollinate in May while
grasses are troublesome in June. Ragweed typically doesn’t become a problem
until August. Keep in mind that in a warm year, these times may be earlier than
the norm.
Phenology can be more than just a hobby for gardeners, it can become a way of life. For centuries farmers have relied on the signs of the seasons to help them grow a crop. In Wisconsin, the Northeast Wisconsin Audubon Society located in Green Bay annually produces a "Weather Friends" calendar that gives phenological information for Wisconsin and Michigan’s upper peninsula. The Dane County Master Gardeners in Madison have also used years of phenological observations to create a gardening calendar to assist gardeners in growing healthy, beautiful plants. And a group of phenological observers at the Wehr Nature Center collect extensive phenological data. You too can use phenology to develop your own calendar and grow a beautiful garden.
Observers are very important to the continued collection of phenological data. If you’re serious about becoming a phenological observer, the Wisconsin Phenological Society is always looking for eyes and ears to help with their observations. As Master Gardeners, you already have an interest in the outdoor world around you. You appreciate the perpetual changes in the natural world around you. And you can discern unusual events from the normal occurrences. If you’re interested in more information on the Wisconsin Phenological Society, contact me at kadelaha@facstaff.wisc.edu.
