How Deep Should Seeds Be Planted?

How does the depth at which seeds are planted affect their germination? What is the maximum depth from which seedlings are able to emerge from the ground? Data that shed some light on these questions can be obtained by planting the seeds along the sides of an aquarium. Start near the bottom and firm the soil with a straight edge or ruler so that it has a slant as shown in the diagram. Add additional layers of soil and continue upward to the surface. A different kind of seed could be planted on each side of the aquarium.

Caution should be exercised in drawing conclusions from this experiment. If the aquarium is kept indoors the temperature will be the same at all depths. Outdoors the temperature usually decreases with depth, especially in the spring.