Plants need to absorb nutrients to support growth whether they are grown using hydroponics techniques or they are grown in soil using conventional cultivation methods. But even with the best nutrients available to them, plants may fail to grow and whither away if a factor known as pH is too high or too low. pH is important because plants can absorb nutrients only if the pH of the nutrient solution is within a range of values that support effective absorption of the nutrients. If the pH of the solution is not what it should be, the absorption process does not proceed normally depriving the plants of nutrients vital for growth.

Macronutrients and Micronutrients

Plants need two types of nutrients, namely macronutrients and micronutrients. When grown outdoors, plants are able to obtain both macronutrients and micronutrients from the soil, but when grown indoors these have to be supplied in the right amounts. There are two types of macronutrients- primary macronutrients namely nitrogen, phosphorus and potassium which are required in large amounts, and secondary macronutrients – sulfur, calcium and magnesium that are required in smaller amounts. The micronutrients iron, manganese, zinc, copper, chlorine, boron and molybdenum are required in even smaller amounts, but are still essential for growth. Each of these macro and micronutrients serves specific purposes for the plants and can be absorbed only when the pH of the solution is conducive to the absorption process. If the pH levels are too high or too low some nutrients become available only at potentially toxic levels, while others simply become completely unavailable.

Understanding pH

pH levels are basically indicative of the acidity or alkalinity of a substance and range from 0 (acid) to 14 (base). A pH of 7 is considered neutral and one that best supports absorption of macro and micronutrients. But for all practical purposes, taking into account other factors like the differences between plants, it is generally accepted that for best results the pH of nutrients solutions should be between 5.5 and 6.8.

The pH scale is structured to represent acidity and alkalinity differentials by a factor of 10. For example, a solution with a pH of 5 is 10 times more acidic than a solution with a pH of 6. Similarly a solution with a pH of 4 is a hundred times more acidic than a solution with a pH of 6. The same applies to alkalinity, though in the reverse order. A solution with a pH of 9 is 10 times more alkaline than a solution with pH of 8.

Monitoring pH

It is known that plants will grow best when the pH of the nutrient solution is between 5.5 and 6.8; obviously therefore, frequent monitoring of pH levels makes sense and several simple methods are available to keep track and make necessary adjustments. Hand held pH meters featuring glass probes offer an easy way to track the pH of nutrient solutions.
These display the pH values on a digital readout when the probes are dipped in the nutrient solution. If the pH is high or low, this can be corrected using suitable pH Up or pH Down liquids. Some of the commonly used pH lowering solutions are nitric acid, phosphoric acid, citric acid and vinegar. Potassium hydroxide is used for raising the pH.

One source of problems that should be taken care of at the outset is the water that is used in the nutrient solution. Before using the water it is good practice take its pH reading and adjust it as needed. Also it is best to avoid using hot water when mixing hydroponics nutrient, because hot water pipes are prone to scaling, and the calcium from the scales can raise pH levels which can be difficult to lower. Finally, indoor growers using rock wool as growing medium need to take measures to offset the inherent alkalinity of the medium. One solution is to use nutrient formulations specifically designed for use with rockwool.

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