Plants grown in hydroponic gardens can't spread their roots out to find the nutrients they need in the soil, so it's up to you to provide them. Many manufacturers make nutrient concentrates specifically for use in hydroponic systems, but it's also possible to make your own from regular fertilizer. Scott's Miracle-Gro fertilizer is a common fertilizer than can be adapted for use in hydroponics.
What Plants Need
Plants need some nutrients, such as carbon, phosphorous and nitrogen, in relatively large amounts, which is why these are known as macronutrients. They also need certain nutrients such as boron, copper, iron and zinc in trace amounts. The trace elements are also known as micronutrients. When creating a hydroponic fertilizer, it's important to make sure that all of the essential nutrients are supplied. If these are missing, plants will have problems such as stunted growth, discolored leaves and wilting.
Which Miracle-Gro to Use
Miracle-Gro is not a single product but is a line of fertilizers made by the Scotts Company. The various products are designed for specific purposes, such as feeding vegetables, azaleas or lawns. When choosing a Miracle-Gro fertilizer to use in a hydroponic system, select a product such as Miracle-Gro All Purpose Water Soluble Fertilizer with Micronutrients. This includes chemicals that many fertilizers don't have and provides the best range of nutrients for your hydroponic plants. Products without the micronutrients can't be used without supplementing them with other fertilizers.
Making the Solution
To make a hydroponic solution using Miracle-Gro, mix 2 teaspoons of the fertilizer with each gallon of water your system requires. Add 1 teaspoon of Epsom salts (magnesium sulfate) per gallon and mix until all of the solids dissolve. Only mix what you will use right away, since the solution will lose strength if you mix it up too far in advance. The water will be blue once you're done mixing.
Things to Consider
Hydroponic plants generally grow best when the pH of the water is anywhere from about 5.5 to 6.0, although many can live in water outside of this range. Test the pH after adding the fertilizer to make sure it falls into the correct range. If not, use a pH adjusting kit -- available at hydroponics supply stores -- to change it. Don't use hydroponic solutions made from Miracle-Gro or other dry fertilizers in drip or aeroponic systems, since even a tiny bit of solid matter can clog the nozzles.
- University of Guam College of Agriculture: Nutrient Concentration and Function in Plants
- Simply Hydroponics and Organics: pH
- Green Coast Hydroponics: FAQs -- Nutrient & pH & Reservoir Maintenance
- Scotts: Miracle-Gro All Purpose Water Soluble Fertilizer with Micronutrients
- University of Florida IFAS Extension: Building a Floating Hydroponic Garden
- Virginia Cooperative Extension: Home Hydroponics