Seeking guidance for Science Fair

I am in the 10th grade in IB chemistry and we are doing science fair this year (not limited to any particular area of science).
I already have a general idea of what i want to do. I want to perform a project where I dissolve Vitamin E in water and then use that solution to water Radish plants and see what effect Vitamin E has on growth of plants. I already know that the IV will be dosages of Vitamin E and the DV will be the growth and development of the plants. And I already know that I need constants like same watering per day and same environment. But I need help on my 5 levels of IV. I know one is a constant that has no vitamin e and just water. But i am stuck on how i should distribute Vitamin E through out the other 4. Should I use capsules and then just dilute them and then do 1, 2, 3, and 4 capsules? Please help. And thank you for reading.