Common fertilizers are formulated with the assumption that plants will obtain some nutrients from the soil they are growing in. The absence of soil in a hydroponic system means that using common fertilizer may lead to less-than-desirable results, although it depends to some degree on the nutrient needs for the kind of plants you plan to grow. University extension Web sites tend to recommend a fertilizer specially formulated for hydroponics, but the University of Florida does suggest you can grow salad greens in a hydroponics solution containing common fertilizer.
Things You'll Need
20-20-20 fertilizer with micronutrients
Soft broom or stirring stick
Fill your hydroponic garden container with the amount of water needed. Keep track of the number of gallons you add.
Add 2 tsp. of 20-20-20 fertilizer with micronutrients for each gallon of water in your system. Also add 1 tsp. of Epsom salts, a form of magnesium sulfate, for each gallon of water. Stir the solution well until you have dissolved all traces of the granules.
Add water to the system once the plants have used up about half of the nutrient solution. Don't add additional nutrient solution because it could cause certain elements in the solution to become so concentrated that they could harm the plants.
Drain the solution every two weeks, and replace it with fresh batch of nutrient solution. This will ensure the plants have an adequate supply of the nutrients needed for proper growth.
You can water other plants with the used hydroponic solution.