Plants require 16 different nutrients for health and growth. In a hydroponic system, no soil is present, so all of these nutrients (except carbon) must be present in the nutrient solution. Hydroponic nutrient solution formulas vary in the amounts of each nutrient, especially formulas designed for different phases of plant life. These nutrients can be supplied from natural organic sources or from food grade or fertilizer grade chemicals.
Carbon, Hydrogen and Oxygen
Carbon is the only required nutrient not taken from the nutrient solution. Plants take carbon from carbon dioxide and release oxygen, recycling the air for human consumption. Hydrogen and oxygen are taken from the water in the nutrient solution for plant use. The other 13 nutrients are added to the water to make up the nutrient solution.
Plants need nitrogen (N), phosphorus (P) and potassium (K) in large amounts. Common recipes for hydroponic nutrient solutions differ in the ratios of nitrogen, potassium and phosphorus. The required amounts of these nutrients change during different periods in the plants life. During heavy vegetative growth phases, plants require more nitrogen. Potassium is required for photosynthesis and plant cell growth. Phosphorus helps seeds germinate and grow. It is important in vegetable and flower crops because it stimulates the plant to bloom and set fruit.
When formulating a nutrient solution from pure chemicals, use ammonium sulfate, calcium nitrate, potassium nitrate, sodium nitrate, urea, or Nitro phoska to supply nitrogen for the plants. Nitro phoska also supplies phosphorus. Monopotassium phosphate supplies potassium and phosphorus. Monocalcium phosphate and monoammonium phosphate supply phosphorus as well. Potassium sulfate and potassium chloride are also used to provide adequate potassium in nutrient solutions.
Secondary nutrients needed by plants in small amounts are calcium, magnesium and sulfur. Magnesium and calcium are found in dolomitic lime and in many fertilizer formulas. The addition of calcium sulfate and magnesium sulfate supply calcium, magnesium and sulfur to the nutrient solution. Additional sulfur can be added in the form of other sulfate nutrients or by adding elemental sulfur.
Plants require Iron, manganese, zinc, copper, boron and molybdenum in very small amounts. The addition of ferrous iron sulfate or chelated iron, manganese sulfate, zinc sulfate, copper sulfate, boric acid, and sodium molybdate provides these nutrients.
Mixing Homemade Nutrient Solutions
Homemade nutrient solutions can be made following Hoagland's, Cooper's, Johnson’s, Larsen's or Jensen’s recipe or your own variation. Adjust the pH of the water to between 5.5 and 5.8 with acid or base, add the nutrients to the water and mix well after each addition. Check the pH again after mixing.
If making a concentrate, you need to make separate solutions that are mixed together to form the final nutrient solution. Mix the primary nutrients, along with the magnesium sulfate in one concentrate. Make a second concentrated solution containing the iron and a third containing the remaining nutrients.
Mix each concentrate solution into pH adjusted water individually, mixing well after each addition.
Commercial Nutrient Solutions
Commercial nutrient solutions contain all of these essential nutrients. Some nutrient solutions are supplied in two-part formulas or three-part formulas. Some of the chemical components interfere with others and are not soluble in high concentrations. Diluting them before mixing solves this problem. Always follow package directions, mixing well after each addition, to make sure all of your nutrients are available to the plants.