Tulips, Temperatures and the Arrival of Spring
Ice melts, leaves emerge and tulips bloom--the winter world comes alive as the earth warms. Scientists have discovered that you can actually measure the amount of heat it takes to make these things happen. This accumulated heat is measured in units called Growing Degree Days. This lesson will help your students understand this concept and see the important role temperature plays in setting the pace of spring's journey.
When to Do This Lesson:
When your tulips emerge from the ground.
Classroom Activity
1. Ask students to think about the steps in baking a cake. The oven must be set at a certain temperature--and the cake must remain in the oven for a certain length of time--in order for it to bake properly. A cake placed in a cold oven won't bake no matter how long it remains there. Ask students how the requirements for baking a cake might be similar to the needs of growing plants. See if they can develop the analogy to explain that it takes a certain amount of heat, accumulated over time, in order for plants to grow.
Also, just as a cake requires a certain temperature, there's a threshold temperature at which plants begin to grow. This is called the base temperature. The base temperature we will use for tulips is 40 degrees. (Note that you will be measuring air temperatures. DO NOT begin to collect data for tulips until you see the tulips emerge from the soil. That is, do not begin until they are exposed to the air.)
2. Show students how to calculate Growing Degree Days using the example below. In order to find out how much heat tulips need to grow and bloom, students will add up the heat the tulips receive every day--as long as it is warmer than 40 degrees, the base temperature.
Here's an Example:
A) Find the Average Daily Temperature
Use your max/min thermometer to measure air temperature each day.
Calculate the daily average according to this equation.
High Temp. + Low Temp. / 2 = Average Daily Temperature
B) Calculate the Heat Accumulated Each Day
Each day, use this equation to calculate the amount of heat your plants have received. These heat units are called Growing Degree Days.
Average Air Temperature- Base Temperature = Growing Degree Days (GDD)
C) Keep a Running Total of Heat Accumulated During the Season.
This chart shows the running total calcluated over a 5 day period.
Day High/Low Average GDD Equation Growing Degree Days
Day 1 45/33 39 39-40 = -1 0
Day 2 50/34 42 42-40 = 2 2
Day 3 50/36 43 43-40 = 3 5
Day 4 52/38 45 45-40 = 5 10
Day 5 54/40 47 47-40 = 7 17
Comments:
* In this example, the high and low temperatures are taken each day and averaged. This gives us the Average Daily Temperature.
* Next, the Base Temperature is subtracted from the Average Daily Temperature. This gives us the GDD value for that day.
* Notice that the GDD value for Day 1 is zero. This is because the average dailytemperature (39 degrees) is below the base temperature (40 degrees). Thus, it was not warm enough on Day 1 for any growth to occur.
* Growing Degree Days are cumulative. Day 1 has zero. We add Day 1 and Day 2 together to get 2. We continue to add the amount of heat the plant receives each day. After 5 days it has received 17 GDD. Explain to students that GDD does not equate to actual days of growth, but is an index of the amount of heat plants have received during the season.
3. Connect with another Journey North classroom. Make predictions, exchange data and compare your results.
4. Begin a tradition! Plant an official Journey North tulip garden each fall. At the end of the Journey North program this spring you will receive planting instructions for next fall. Please note that your results will vary widely if you have not planted the specific early blooming tulip variety designated for this experiment.
Discussion
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