pH And Nutrient Availability: What To Know

pH For Hydroponics


Before we get started, if you haven’t read my hydroponic nutrients guide, hop on over there now and educate yourself! OK, let’s talk about a crucial step in your hydroponics education – pH and nutrient availability.

We have already learned what plants need to survive:

  • Light
  • Water
  • Nutrients
  • Oxygen
  • Carbon dioxide

In this article, we’ll take a look at just two of these: water and nutrients.

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pH: What is it and Why Does it Matter?

You might remember pH from your high school chemistry classes. It is a measure of the acidity or basicity of a solution. It’s measured on a scale from 1-14. A pH of 1 is considered an extremely acidic solution, and a pH of 14 being a highly basic solution. Absolutely pure water is considered a 7.0 on the scale – otherwise known as pH neutral.

Without knowing the basics of pH, you’re likely to cause catastrophic problems for your hydroponic garden. Because you are forgoing the use of soil in hydroponics, it’s crucial to keep a watchful eye on the pH of your nutrient solution.

The optimal range for most plants is anywhere from 5.5-6.5. A pH in this range has a few advantages for us. First, we’re working with nutrients dissolved in water, not soil, so we can immediately discount the diseases and pests that plague traditional soil gardens. Additionally, with a slightly acidic pH, a lot of the waterborne algae varieties have a hard time growing. However, the most important reason to keep your pH between 5.5-6.5 is to avoid something called nutrient lockout.

Don’t Throw Your Nutrients in Jail

The pH of your nutrient reservoir affects how plants absorb nutrients. A pH that is too high or too low can completely shut down the ability of your plants’ roots to absorb nutrients. This is clearly bad – a well-balanced nutrient reservoir not only contains the right concentration of nutrients in relation to water, but the solution itself must also be within the correct range. Only then can you have a truly balanced nutrient reservoir.

pH and Nutrient Availability
Nutrients and the pH ranges that lock them out.

The chart above lists the most essential nutrients plants need for vigorous growth. Along with that list is a horizontal representation of the availability of each of these nutrients as you move along the pH scale. The thickness/thinness of each line of nutrients represents the ability of a plant to absorb that particular nutrient at a specific pH level.

As you can see, plants find almost every nutrient hard to absorb at the far ends of the pH scale. However, you don’t have to be too far off balance to hinder the growth of your plants. Take a look at pH 5.0. Here, our plants have trouble absorbing the three macronutrients as well as a handful of other nutrients. This is why maintaining a balanced pH is extremely important – small errors can hurt your plants. The “sweet spot” is generally considered to be around 6.2, although different plants require different pH levels.

Most liquid nutrients come with pH buffers. These ensure that your water is pH corrected within the 5.5-6.5 range, which is really handy for hydroponic growers. However, this doesn’t mean that you can completely forget about monitoring your pH. The uptake of nutrients and water by your plants will cause the pH to fluctuate. It’s very important to have a simple pH testing kit to keep track of your nutrient reservoir’s pH levels.

Well, there we have it. The basics of pH and nutrient availability for your hydroponic gardens! There’s more to the picture – there always is – but for now, this introductory guide will work just fine.

If you’re feeling excited, head on over to the next article in my Hydroponics From Scratch seriesHydroponic Growing Media.