pHrustrated? Get the pHacts on Nutrients and pH

You may have some idea that pH is important, but you may not know why. If the pH of your nutrient solution is too high or too low, your plants won't be able to take in nutrients as well as they should.

What Plants Need

Because plants need nitrogen, phosphorus, and potassium in large amounts, these elements are known as primary macronutrients. Plants need smaller amounts of the secondary macronutrients-sulfur, calcium, and magnesium . Iron, manganese, zinc, copper, chlorine, boron, and molybdenum are still essential for growth but are required in even smaller amounts. They are often referred to as micronutrients or trace elements. Each of these macro- and micronutrients serves specific purposes for our plants, and, for plants grown indoors, it's up to us to make sure we supply them. If pH levels climb too high or fall too low, some nutrients become available to your plants at toxic levels while others become completely unavailable.

pH Basics

Ranging from 0 (acid) to 14 (base), the pH scale is used to determine the acidity or alkalinity of a substance. Plants growing in hydroponics solutions which are either too acidic or too basic have trouble absorbing what they need for steady growth. A pH of 7 is considered neutral, and, for optimal nutrient uptake, the pH of your nutrient solution should be between 5.5 and 6.8 depending on the types of plants you'll be growing.

Every full point change along the pH scale represents an increase or decrease in acidity or alkalinity by a factor of 10. For instance, a solution with a pH of 5 is 10 times more acid than one with a pH of 6. If you were to step down to a pH of 4, the solution would be 100 times more acid than a solution measuring pH 6.

Tracking and Adjusting pH

You know your plants will flourish when their nutrient solution is between 5.5 and 6.8, but how can you ensure that conditions will be just right? Many different variables such as evaporation, temperature, and amount of light can affect pH levels. As such, frequent monitoring of nutrient solution pH levels is a good idea.

If you aren't using a pH monitor that remains directly in the nutrient bath to offer continuous readings, you'll need to measure the pH of your nutrient solution at least twice a week with a hand-held pH meter. Hand-held meters feature delicate glass probe tips which are dipped into nutrient solution for periodic testing, and they offer easy-to-read digital results right away.

If you find that your solution is too acidic or too alkaline, you can make incremental changes in pH with PH Up or pH Down liquids as needed. Some solutions commonly used to lower pH include nitric acid, phosphoric acid, citric acid, and vinegar. Potassium hydroxide is typically used to raise pH.

Before You Mix . . .

Finally, to prevent possible problems, take a pH reading of the water you will be using and adjust it as needed before mixing your nutrient solution, and never use hot water when mixing hydroponics nutrient. (The 'scale' that you see on the inside of hot water pipes is a form of calcium that will raise your pH to irritating levels which cannot easily be reduced.)

Also, indoor growers using rockwool may need to compensate for the growing medium's inherent alkalinity which can cause pH shifts. In addition to pre-soaking your rockwool over a 24-hour period, you can use a nutrient which is specifically formulated for use with rockwool.