Plants grown in a hydroponic system tend to be healthier due to the elimination of soil-borne diseases and pests. You can buy a hydroponic system, but these tend to be expensive, especially if you want a large system which can sustain many plants. With a few inexpensive materials, you can build a homemade hydroponic grower and adjust the size to suit your needs.
Level the ground in the area where you will be placing your hydroponic grower and remove any debris such as sticks or roots which could puncture your plastic liner.
Build a frame for your grower using 2-by-6 inch treated lumber; to keep from having to trim the Styrofoam sheets, build your frame 4 feet 1 inch wide by 8 feet 1 inch long. The size can be adjusted to fit your personal preferences; however; you'll need to trim the Styrofoam to fit.
Line the hydroponic grower frame with a polyethylene plastic sheet; attach one end and one side of the liner to the top edge of the frame by nailing a 2-inch-wide lattice strip to the frame with the plastic between.
Cut holes in the Styrofoam sheet to hold your plants. If you are using 3-inch net pots, you will need a 2 1/2-inch hole saw; if using 2 -inch net pots, your hole saw should cut a diameter of 1 3/4 inch. The holes in the Styrofoam should be small enough so that the bottoms of the net pots stay level with the underside of the Styrofoam sheet. This allows the roots to wick up water without being totally submerged.
Space the holes in the Styrofoam 6 inches from the sides and 12 inches apart; this should leave you with 32 planting holes.
Place your Styrofoam sheet into the lined frame and check that it has enough room around the edges to move up and down inside the grower. Remove the sheet while you mix the nutrients.
Add 20 gallons of water to the water garden to force the plastic sheeting to conform to the sides of the grower, then secure the other end and side of the liner to the frame.
Fill the hydroponic grower to a depth of at least 5 inches, keeping count of the number of gallons of water you add.
Mix water-soluble 20-20-20 fertilizer that includes micronutrients into the grower; add 2 tsp. fertilizer for each gallon of water.
Add 1 tsp. Epsom salts for each gallon of water and stir the nutrient solution with a soft broom to prevent damaging the liner.
Adjust the nutrient solution after a heavy rain which floods the grower; if you don't know the amount of water added to the grower, you will need to change the solution.
Place the Styrofoam sheet back into the filled hydroponic grower.
Transplant your seedlings into the net pots and place them into the holes in the Styrofoam sheet.
Add nutrient solution as needed to keep at least 5 inches of solution under the Styrofoam sheet.