The goal is to have the student test a hypothesis about seed germination and the phases of the moon by conducting a controlled experiment.
How does the phase of the moon affect moisture capillarity in garden soil?
The gravitational attraction between the Earth and the Moon produces two bulges in the ocean on opposite sides of the Earth. The water in the ocean on the side of the Earth closest to the moon experiences a larger gravitational attraction than the water on the opposite side. As a result the water on the near side is pulled away from the Earth while the water on the distant side is pulled toward the Earth. Any given point of the Earth’s surface experiences two high tides and tow low tides with each rotation.
According to gardening lore, seeds planted between the new moon and the full moon show better germination characteristics than those planted at other times of the month. The argument given is that the gravitational pull on the Earth’s water is greatest at this time, and that this causes water in the soil to come to the surface where it is available to the germinating seeds.
Upward movement of water in the soil (capillarity) occurs when lower soil layers contain more moisture than upper soil layers. The height that the water rises to depends on the soil pore size -- the smaller the pores, the more the capillary rise. This is the process that allows moisture to be absorbed by a plant’s roots.
- Commercial gardening soil
- Soil moisture sensor
Materials can be found at: Garden nursery or Internet
- Read about the effects of the moon on the Earth’s tides, and propose a hypothesis that predicts whether the moon will influence the growth rate of plant seedlings by drawing water to the ground’s surface.
- Consult a calendar for the dates of the new moon and full moon.
- On the day before the new moon, measure out and place a small amount of water in the bottom of a soup bowl.
- Cover the water in the bowl with about six inches of commercial garden soil. Pack the soil down firmly.
- Using a soil moisture indicator, measure and record the depth at which moisture is first detected.
The moisture should initially be detected near the bottom of the bowl. If this is not the case, empty the bowl and start over using less water.
- Measure and record the depth at which water is first detected on each successive day between the new moon and the full moon.
- On the day of the full moon -- after making the last measurement in the first part of the experiment, remove the soil from the bowl. Replace it with the same amounts of water and commercial soil used earlier. Pack the soil down firmly.
- Measure and record the depth at which moisture is first detected on each successive day until the next new moon.
- Compare the results for the two monitored periods.
- Evaluate your hypothesis in light of you data. If necessary revise it, and propose additional experiments.
Day 1 (New Moon)
Day 16 (Full Moon)
Day 16 (Full Moon)
Day 31 (New Moon)
Terms/Concepts:Gravitation; Tides; Capillarity