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Simulating Threshold Effects of Soil pH on Hydrangea Plants

kit #320

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.

Accommodates three classes, each with 6 groups of four students.
For larger class sizes you can ADD A GROUP to accommodate one additional group of four students.

  • Laboratory testing is often used to help establish positive and negative (toxic) threshold levels for substances.
  • Quantitative data derived from tests can be mathematically extrapolated.
  • Several factors must be considered when extrapolating lab-derived data.

Content List in Simulating Threshold Effects of Soil pH on Hydrangea Plants is as follows:

Quantity Description
12 Chemplates® with stir sticks
12 red/blue pencils
6 15-mL dropper bottles of “agricultural lime”
3 30-mL dropper bottles of “plant mass”
3 30-mL dropper bottles of “soil aluminum”
3 30-mL dropper bottles of “plant nutrients”
1 Material Data Safety Sheet (MSDS) booklet
available as downloads Teacher's Guide, Student Worksheet and Guide, MSDS booklet
number of groups
maximum 6 per class period
number of students
maximum 24
Downloadable text-based teacher and student materials
Printable .pdf files for text-based teacher and student materials can be downloaded by filling in the registration form (found in the Intro Video tab) then clicking on the pdf version of each file shown.

The .pdf files are ready for printing and for importing into the Notability App. The .doc/.rtf version of the Student Worksheet and Guide is supplied so that students can open these files on a computer or tablet, enter their responses, then submit their completed e-file via email. The .doc/.rtf version is also editable to provide the teacher the capability to customize the Student Worksheet and Guide.

Because we are continually striving to improve our products, if you find any errors or trouble spots or have any suggestions for improvement (e.g. different questions, possible extensions, etc.) please send them to:

This activity will require one to two ~50-minute class periods to complete.

Title Item # Price Quantity
Simulating Threshold Effects of Soil pH on Hydrangea Plants 320 $122.50
ADD A GROUP for Simulating Threshold Effects of Soil pH on Hydrangea Plants 320EL $26.35
"Plant Nutrients", 30 mL bottle 320-B04E $4.05
"Soil Aluminum", 30 mL bottle 320-B03E $4.05
"Plant Mass", 30 mL bottle 320-B02E $4.05
"Agricultural Lime", 15 mL bottle 320-B01E $3.60