Tracking Seasons

By Eve Pranis

In the spring, longer days and warmer temperatures trigger sap to run, buds to swell and bloom, and birds and insects to appear.

People living close to the land are acutely aware of these changes in nature that are influenced by weather and climate. The term for the study of these seasonal weather-influenced changes in plants and animals is phenology. The amount of sunlight, which affects day length and temperature, is the main factor driving these shifts. In the spring, for instance, increasing sunlight and resulting warming temperatures trigger plants to emerge and grow. This prompts animals who depend on these plants to migrate, leave hibernation, and/or reproduce; predators that depend on those animals also thrive.

Since different plants and animals tend to respond to environmental factors in predictable ways, native people took cues from nature to determine when to plant their crops. For example, some early settlers were told by native people in New England to plant corn when the white oak leaves were the size of a mouse's ear or the red squirrel's footprint.

Were these suggestions fact or fiction? Since plants and animals do respond to temperatures, soil moisture, day length, and other factors, it makes sense that we can take cues from these natural occurrences. In fact, many farmers and gardeners today still use this kind of information. For instance, they predict hatching of certain pests, then time pest control strategies based on bloom times of selected plants.

Invite your students to be sleuths who track the progress of the seasons. Consider the following activities.

Observe Seasonal Signs

Have students brainstorm signs that spring (or fall) is approaching, then keep a running class chart of observations. Be sure to note climatic factors such as temperature, day length, sun's movement, precipitation, and so on, as well as plant and animal cues. What are the sounds, smells, colors, and feelings that accompany these changes? How does the soil feel? When do different insects appear? Consider surveying other students, parents, and teachers for more spring signs to add to your list. What changes can be predicted with accuracy (e.g., length of sun's shadow at different times, spring equinox, last day of school) versus factors that vary from year to year based on weather (bulbs blooming, ice out, first robin)?

Find Mystery Partners

Partner up with a class in a "mystery" school in another location. Consider finding one through our E-Mail Pals or School Garden Registry features. Don't reveal the school's location to your students. Have students exchange weather, phenology, and/or gardening information that could give clues about the schools' locations. For instance, have students in both schools measure the sun's shadow with a meter stick at noon on the same day each month, then share information about its length. Are pussy willows blooming? How high are daffodils? Which plants are being set out in the garden? Consider tracking the progress of one particular type of plant in different areas. (Some widely distributed plants to use to track spring's progress include lilac, redbud, serviceberry, sugar maple, and quaking aspen.)

Journey North Tulip Project. Through this exemplary project, students can measure spring's northward journey by growing tulips and exchanging data with classrooms around the country. It includes extensive background information and instructional ideas as well as a classroom phenology exchange program. Visit the project at its web site (

Measure Spring's Heat

The world seems to come alive as the earth warms in the spring. It takes a certain amount of heat to coax plants to begin to grow. For instance, peas are cool-weather lovers and will germinate at 40 degrees F, while corn needs temperatures of at least 50 degrees F. Spring tulips need base temperatures of at least 40 degrees F to grow at all. In order to reach maturity, plants need a certain amount of heat accumulated over time, much like a cake baking in an oven. This heat is measured in units called Growing Degree Days.

A Matter of Degrees

Your students can actually measure the amount of heat it takes to make these things happen. Here's how they can calculate the Growing Degree Days accumulated during a period of time:

* Find the mean daily temperature by adding the high and low for the day and dividing by two

* Calculate the heat accumulated each day for the crop: mean temperature minus the base for that crop (e.g., 40 degrees F for tulips, 50 degrees F for corn). That equals the growing degree days (0 if it's a negative number).

* Keep a total of growing degree days accumulated through season.

Consider connecting with another classroom in a different area, then try growing the same crop and comparing the number of Growing Degree Days it takes to mature. Ask students, If you grow the same species of daffodil in two different climates, do you think it will take the same growing degree days for the flowers to bloom? Why or why not? If a seed catalog or packet says that something takes 60 days to maturity, do you think it will always take that exact number of days? Why or why not? How could you test this?

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