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Tulips, Temperatures, and the Arrival of SpringMeasuring the Amount of Heat Required for Your Tulips to Grow and BloomIce melts, leaves emerge and tulips bloomthe winter world comes alive as the earth warms. Scientists have discovered that you can actually measure the amount of heat it takes to make some spring events occur. This accumulated heat is measured in units called "Growing Degree Days". This activity will help students understand this concept. As they measure temperatures each day, they can analyze the role temperature plays in setting the pace of spring's arrival. Activity: 1. Ask students to think about the steps in baking a cake. The oven must be set at a certain temperatureand the cake must remain in the oven for a certain length of timein 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 for proper baking, 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. That is, we only expect tulips to grow on days the temperature is above 40 degrees F. When it's below 40 degrees F, we don't expect any growth to occur. 2. In order to find out how much heat tulips need to grow and bloom, students will add up the heat received every dayas long as it is warmer than 40 degrees, the base temperature.
STEP A: Measure the High and Low Air Temperature Each Day
STEP B: Find the Average Daily Temperature To calculate the average daily temperature, first add the high and low temperatures. Then divide by two. Here is the equation: High Temp. + Low Temp. / 2 = Average Daily Temperature STEP C: Calculate the Amount of Heat Accumulated Each Day Each day, use the Growing Degree Day equation to calcuate the amount of heat your plants have received. Subtract the base temperature from the average daily temperature. These daily units of heat are called "Growing Degree Days". Average Air Temperature Base Temperature = Growing Degree Days STEP D: Keep a Running Total of Heat Accumulated During the Season. Notes:
SAMPLE CHART 
DATE  Today's Temperature  Base Temp. for Tulips  Today's Growing Degree Day Value 
TOTAL Growing Degree Days 


Hi  Lo  Av  (Av. Temp)  (Base Temp)  = GDD  
2/3/97  45  33  39  40 F  39 40  1  0 
2/4/97  50  34  42  40 F  42  40  2  2 
2/5/97  50  36  43  40 F  43  40  3  5 
2/6/97  52  38  45  40 F  45  40  5  10 
2/7/97  54  40  47  40 F  47  40  7  17 
2/8/97  52  42  40 F  
2/9/97  60  40  40 F 