Plants that grow in stressful conditions often produce large seeds. In contrast, a large number of small seeds are common when there is adequate water and light. Let elementary school children arrange seeds according to size; do not show the picture of the plant. Plant seeds, such as tomato, lettuce, sweet pea and broad bean, in pots of the same size. Let the students guess which seed is going to grow into which plant.
You can find seeds inside pods or in hard shells. Bean seeds are large and can be slit open to display the tiny baby plant inside. Soak bean seeds in water for a day or two. A soft outside covering will appear, which you can remove. Open the bean seed along the slit. The bean will separate into two oval shaped halves. You can see the leaves of the new bean plant at one end and the roots at the other end. Let elementary school students use magnifying glass to examine the baby plant. Plant bean seeds in various directions in the dirt. Explain to the students that gravity will make the roots to grow downwards.
An engaging seed planting experiment is to examine if music and talking to the plants influence the growth. Use five pots of the same size. Sprinkle radish seeds on moist soil in the pots. Mark the pots and treat the pots differently. Ignore one pot. Let students say "Hello" in a grumpy voice to the second pot and say "Hello" in a friendly voice and smile to the plant in the third pot. The fourth pot gets a lot of attention, and students can talk to the plant and stroke the leaves. Ask them to tell the plants that they look beautiful. Play soft music a couple of times a day to the plant in the fifth pot. The plants that receive positive attention may grow quicker. Observe the plant size and leaf color.
Planting material and soil temperature affect the growth. Plant winter lettuce in pots and vary the growing conditions. Sprinkle some seeds over sand, garden compost and soil. Plant two sets of each soil material. Put one set of pots outdoors or in cooler conditions, and the matching half in warmer conditions. Lettuce seeds are fine and they grow best in finer soil. The best soil temperature is between 40 to 70 F. The lettuce in the warmer conditions will grow faster, but the soil type may influence the result.