Simulating Threshold Effects of Soil pH on Hydrangea Plants

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Product Number: C34436

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Grades 6-12.

In this simulation activity, students model how hydrangea plants are affected by soil pH. Agricultural lime (mostly CaCO3) is often used to adjust soil pH. Soil pH is a factor that influences the color of hydrangea flowers and the health of the plant. Below a positive threshold pH, hydrangea flowers are blue, above this threshold dose flowers are pink, and higher doses, above the negative threshold amount, cause health problems. The use of a simulation allows students to add agricultural lime to each plant and then immediately observe the plant's reaction. Students use the data obtained from the simulation to determine the positive and negative threshold doses for agricultural lime. They also reflect upon the results to decide whether they have sufficient data to make a recommendation for an optimal amount of lime to use if you want to produce healthy plants with pink flowers.


  • 12 Chemplates® with stir sticks
  • 12 red/blue pencils
  • Six 15 ml dropper bottles of agricultural lime
  • Three 30 ml dropper bottles of plant mass
  • Three 30 ml dropper bottles of soil aluminum
  • Three 30 ml dropper bottles of plant nutrients
  • Material Data Safety Sheet (MSDS) booklet.

A student worksheet and guide, plus a teacher's guide, are available as downloads.

WARNING: Choking Hazard. Small Parts. Not for children under 3 yrs.

Item Weight: 2.25
Age: 11 yrs. - 18 yrs.
Grade: 6 - 12
School Type: Middle School, High School
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