Wisconsin Fast Plants Network

To know a plant, grow a plant!

Questions have been coming in from teachers who are working on various teacher-guided and student-centered inquiries regarding the logistics for growing Fast Plants. In particular, for teachers new to Fast Plants there are early decisions to be made about what type of growing system to use and how many plants to thin to in each growing system.

We welcome your comments about how you decide the number of plants to thin to in bottle or deli-container growing systems or other logistics you navigate when planning for class experiments.

The following is a response I wrote to a question about how many plants to have students thin to in bottle growing systems. Because my answer is it depends, the answer comes in the form of a scenario:

How do I determine how many plants I want to have growing in each Fast Plant growing system if I'm not using quads (which are pre-determined to have 4 plants per growing system--1 plant/cell in the quad)?

Response: Depending on what your learning objectives are for students, we recommend that each student be able to carefully observe one individual plant that is "their" plant throughout the time when you are growing, and this can help to guide your choice of container size and number of plants/container or growing system.
I recommend growing the same number of plants as the number of students you'll have grouped together, sharing a growing system. Consider this example scenario:
Potential inquiry questions
  • What is the range of temperatures in which Fast Plants can survive and grow?
  • How is __(e.g. # days to flower, plant height, # days to first true leaf, cotyledon size, etc.)__ affected by temperature?
  • How is seed production (reproductive success) in Fast Plants affected by the temperatures at either end of the range in which they can grow (i.e. at the coldest and warmest ends of the temperature range)?
Experimental Design
Student groups grow one growing system that is their control (kept at ~72-82 degrees F, as recommended in the standard Fast Plants growing protocol given to all student groups by their teacher) and each group devises various ways to grow one growing system planted with Fast Plants in a particular temperature outside of the "ideal" temperatures prescribed in the standard protocol. (This would be guided by the teacher such that the class or a mix of classes has plants growing Fast Plants all along and just beyond the range of temperatures that Fast Plants can tolerate-- ~40-65 for the cold end and ~85-100 or more on the hot end of the spectrum.)
Controlling for light intensity and all other environmental variables as much as possible, student groups all grow their experimental plants in conditions that elevate or lower the temperatures (e.g. a bottle growing system is placed in a refrigerator with a clamp lamp rigged in place so that they have light but the temperature is low, or a lightbox is made with a curtain to retain the heat from the light, or a heat lamp is added to a light box, or some plants are grown in a cool closet or near a drafty window -- still with the addition of fluorescent light, so only the temperature (under the lights--where the plants are growing) is altered.
All students groups also grow their control plants in the same place where standard conditions are maintained.
Then, students each observe and record one control plant and one experimental plant in their group's growing systems throughout the time when the plants are grown. Those data they record are determined by the inquiry question(s) asked and the learning goals (data recorded might include plant height, cotyledon size, #days to flower, # seeds produced, etc.).
Growing system  Could be a 2 liter bottle growing system or a smaller, 16 oz bottle growing system, or a deli-container growing system, or something you've designed for your class.
Student group size = 4 students/group
# Plants / Growing System = Here's where knowing the number of students who are sharing a growing system can determine how many plants you want to have growing in each system.
If students are going to work in groups of 4, sharing a growing system, then having 4 plants in each growing system makes good sense. Then, each plant can be numbered or named with a marker or colored toothpick or some indicator that will make it possible for each student to record data on the same plant each time. This will be very important for their data to have meaning.
Planning for good group dynamics during data collection is important, too. It's really hard for four students to gather around one growing system to measure and carefully observe their own plant. However, if -- as in the design described above -- a group of 4 students are sharing 2 Bottle Growing Systems (one control and one experimental planting), then students can work in pairs to observe one and then the other growing system. This will minimize the number of times when one or more students in the group will be idle, waiting for one of their plants to observe.

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