|MadSci Network: Botany|
Hi Megan. What a good science project.
You will need to use only one type of plant.
Use the same type of pot or container and the same material to grow the plant in. I suggest that you use plain washed sand. You will probably find this in a pet store or plant nursery.
Sit each pot in a separate container with water part way up. The sand should stay moist all the time. You might like to plant corn or broad bean seeds.
Gray water will contain detergents [dish washing, shampoo, clothes washing]. It will also contain food scraps, soil, bacteria, chemicals.
You need to collect enough for the experiment.
You might have say 12 pots in pairs. Plant one seed in each pot.
In the first just have sand and seeds. In the second pair add a spoonful of gray water each day. In the third pair add two spoons full and the fourth three spoons full and the fifth 4 and the last 5 spoons.
Over the next couple of weeks take photos, and keep notes on what happens. Make a display. Good luck.
Try the links in the MadSci Library for more information on Botany.