(Level of difficulty **)
Question: Is growth of plants affected by how crowded they are?
Materials you will need:
•4 empty rinsed plastic yogurt containers or single-use cups (any size, preferably 3-10 oz)
• Larger plastic or Styrofoam tray(s) or bowl(s)
•An awl
•Soil (dirt from outside should work)
•Seeds (bean, pea, cucumber, tomato, sunflower, corn, pumpkin or squash)
•Water (tap water is fine)
Directions:
•Poke small holes (1-3 per container) on the bottom of yogurt containers or cups using an awl (have an adult help you with that!)
•Fill containers with soil and place them in a larger bowl/tray (to capture spills and leaks)
•Pour some water onto the soil to make it moist, but do not overwater (stop watering as soon as you see excess water coming out from the holes onto the tray)
•Put the seeds in soil (add 1, 3, 10 and 20 seeds to the four different pots) and cover them with a little bit of soil (finger-thick layer or less)
•Put all 4 containers next to the source of light (a windowsill).
•Wait for 3-14 days for the seeds to germinate
•Observe plant growth over time
Helpful hints and suggestions:
•Don’t forget to label the containers (for example “1” , “3”, “10”, and “20”), so after your experiment is done you will not get confused which pot is which (is this necessary here?).
•Dependent on what kind of seeds you planted and how fresh they are, it may take a very different amount of time for the seeds to germinate and grow.
•Don’t forget to water your plants! The easiest way to water the plants is to add water to the dish/tray your pots are sitting in: the soil and the plant roots will take up the water through the hole that you drilled!
Expected results:
•Seeds should germinate in all pots at about the same time.
•At the beginning, seedlings in all pots will look about the same, but over time the more crowded plants will lag behind in growth
Follow-up questions:
•Why do you think germination of seedlings is not dramatically affected by the seed number?
•Why do you think overcrowded seedlings will grow smaller than the less crowded ones?
•Which resources (such as water, nutrients, light, air) do you think the plants would need to grow and what may be limiting their growth in the overcrowded pots?
•Do you think the results of this experiment would be different if you did the experiment in the dark?
•If you were to repeat the experiment, would you get the same results?
•What would happen if you used another kind of seeds?