Plants that grow in soil receive the nutrients they need from the soil itself, including both the macronutrient nitrogen (N), phosphorus (PO) and potassium (K), as well as the micronutrients needed in smaller amounts. Hydroponic plants grow in a nutrient solution instead of soil. The nutrient solution supplies plants the nutrition they need through a mixture of minerals and water. Building a hydroponic system to grow a plant does not require expensive equipment or a great knowledge of chemistry.
Cut holes into the foam board using the foam cups as a guide, using your knife so that the cups protrude through the board 2 inches. Space the cups far enough apart so that they have ample room for a mature plant, depending on the variety (for example lettuce requires 8 to 10 inches form the center of one cup to another).
Poke 1 hole into the bottom and 4 holes into the sides of the cup using a pencil.
Fill the cup partially with a garden growing medium, also called substrate, that does not contain soil. The Alabama Cooperative Extension recommends perlite, coarse sand, vermiculite or rock wool.
Mix the nutrient solution according to the instructions on the packaging. Test the solution using your pH test to determine whether it is at the correct pH level, between 5.0 and 6.0.
Place your seedling into the foam cup partially filled with perlite or substrate and cover the roots. Moisten the substrate with the hydroponic solution.
Fill the plastic container with the rest of the nutrient solution so that it touches the bottom of the cups when the foam board is placed on top. Rest the foam board in place.
Let the nutrient solution drop to 1 to 2 inches below the cups as roots protrude from the bottom. As the nutrient solution lowers, perform regular pH tests to determine whether the pH level is correct. Add water to balance out the acidity as nutrients condense.