Teacher resources and professional development across the curriculum

Teacher professional development and classroom resources across the curriculum

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Life Science: Field Population System

Building Your Field Population System

One Field Population System requires a “Bottle Growing System” plus the appropriate seeds. If you follow “Assessing Variation” with “Selective Herbivory,” you can use the same Bottle Growing Systems. Both of these activities require Fast Plant, turnip, and lettuce seeds and the latter requires cabbage white butterfly eggs. In addition, you’ll need a Brassica Nursery* to rear the butterflies to the larval stage, a Light House* to grow all of the plants, and a Bee Stick* for pollination. “Salt of the Earth” can use any seeds — we recommend Fast Plants because of their rapid life cycle.

*Note: The instructions for the Brassica Nursery, Light House, and Bee Stick are provided as part of the Brassica & Butterfly System.

field population system

Materials Needed

For Building Bottle Growing Systems

  • One one-liter plastic bottle (provides a top unit and deep base unit)
  • One bottle cap (for deep base unit)
  • One 10-cm length of nylon craft cord (for wick)
  • China or non-permanent marker (for making marks)
  • Safety razor or utility knife (for starting bottle cuts)
  • Scissors (for finishing bottle cuts)
  • Soldering iron or drill (for making wick hole in bottle cap)

Assessing Variation” requires at least one Bottle Growing System — you’ll want to prepare three if you follow it with “Selective Herbivory.” “Selective Herbivory” requires three Bottle Growing Systems. “Salt of the Earth” also requires three.

For Stocking and Maintaining (Assessing Variation and Selective Herbivory)

  • One package of Fast Plant (Brassica rapa) seeds
  • One package of purple top white globe turnip seeds
  • One package of lettuce seeds
  • Cabbage White Butterfly eggs
  • Potting soil mix (Jiffy-Mix©, Scott’s Redi-Earth©, or 1:1 peat moss and vermiculite)
  • Fertilizer solution (Peters Professional TM Fertilizer or Miracle Gro)


  • “Salt of the Earth” requires only Fast Plant seeds.
  • Each Field Population System for “Assessing Variation” and “Selective Herbivory” requires 10 - 15 seeds of each type. Be sure to order enough Fast Plant seeds for all of the activities you plan to do.
  • Fast Plant seeds and butterfly eggs can be ordered from Carolina Biological Supply Company (1-800-334-5551) or www.carolinabiological.com. They can also be ordered from www.bottlebiology.com.

Building Instructions

  1. Follow the instructions for making cuts, in “Bottle Basics,” to make a top unit and a deep base with each bottle.
  2. Melt or drill a hole in the bottle caps and screw onto each top unit.
  3. Insert wick through hole in bottle cap with approximately 5 cm on either side.
  4. Invert the top unit over the deep base.

Stocking Instructions

For Assessing Variation and Selective Herbivory

  1. Moisten the potting mix.
  2. Fill the top unit with potting mix to about 5cm from the rim.
  3. Apply water gently to the mix until dripping from the wick below.
  4. Add more potting mix until settled but be careful not to pack too heavily.
  5. Mix equal numbers of each seed together (10 - 15 seeds for each system).
  6. Scatter the seeds in the system, taking care to distribute them as evenly as possible.
  7. Cover the seeds lightly with a thin layer of potting mix.
  8. Fill the deep base about 3/4 full with fertilizer solution (follow instructions on fertilizer container)
  9. Place in Light House, elevating so that the plants will sprout about 10cm from the light.


For “Salt Of the Earth,” use only Fast Plant seeds. Sow 20 – 25 seeds in each system.

Maintenance Instructions

  1. Keep deep bases supplied with fertilizer solution.
  2. Thin seedlings as needed so that only single plants are growing from the same place.
  3. Adjust plants as they grow to maintain approximately 10cm distance to light.
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