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Size vs. Depth: The Relationship Between the Size of a Seed and Its Ideal Planting Depth

Time Required Very Long (1+ months)
Material Availability Readily available
Cost Low ($20 - $50)


Plants have evolved many clever mechanisms to ensure that their seeds will wait for appropriate conditions before sprouting. Some may only germinate after a fire, others only after going through a cold spell. This project explores one important variable among many that determine the ideal conditions for seed germination.


The purpose of this project is to find if the size of the seed determines the ideal planting depth.

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Last edit date: 2013-01-10


You may think planting seeds is as simple as putting them in the ground and giving them water. But did you realize that there are a number of different types of seeds that require different conditions to grow? Some seeds may need light to grow, some may need darkness, and some may even need to be charred by fire. So with all these variations in the ideal conditions to stimulate seed germination how does seed size impact the process of germination? Do certain size seeds need special conditions?

Terms and Concepts

To understand the relationship between planting depth and seed size, you should have solid understanding of the seed germination process, the structure of a seed, and the factors that break dormancy for different size seeds.


Some sources for information on germination and seed structure:

Materials and Equipment

  • Seeds. We recommend using the following sedds for this project:
    • Garden pea
    • Supersweet corn
    • Onion
    • Lima bean
    • White pinto bean
    • Radish
    • Lettuce
  • Scale (for recording weight)
  • Ruler (for measuring seed size, plant growth, and planting depth)
  • Pots
  • Potting soil
  • Tape or popsicle sticks to mark each of the pots with the type of plant and planting depth

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Experimental Procedure

  • Select the types of legume seeds you will be using for the experiment.
  • For each seed type, record the weight, size, and recommended planting depth
  • For each seed type, determine the planting depths that you will use for this experiment. Here is a recommendation for determining the different depths:
    • Depth 1: recommended planting depth
    • Depth 2: surface
    • Depth 3: two times the recommended planting depth (this will be your deepest seed)
    • Depth 4: half way between the surface and the recommended planting depth
    • Depth 5: half way between the recommended planting depth and the deepest seed (which is twice the recommended planting depth)
  • For each seed type, plant the seed in a pot at each of the depths. (So if you are using 6 different types of seeds, you will have 30 pots, one for each seed type at each depth)
  • You should repeat this experiment at least twice to ensure you get enough data for each seed type at each of the depths.
  • After about 17 days, measure and record the heights of each of the plants.

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Is there a relationship between seed size and the amount of light needed to germinate seeds?

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