pH - Why It's Important

The pH scale, from 1 to 14, measures acid-to-alkaline balance. The number 1 is the most acidic, 7 is neutral, and 14 most alkaline. Every full-point change in pH signifies a ten-fold increase or decrease in acidity or alkalinity. For example, soil or water with a pH of 5 is ten times more acidic than water or soil with a pH of 6. Water with a pH of 5 is one hundred times more acidic than water with a pH of 7. With a ten-fold difference between each point on the scale, accurate measurement and control is essential to a strong, healthy garden.

Most plants grow best in soil with a pH from 6.5 to 7. Within this range plants can properly absorb and process available nutrients most efficiently. If the pH is too low (acidic), acid salts chemically blind nutrients, and the roots are unable to absorb them. An alkaline soil with a high pH causes nutrients to become unavailable. Toxic salt buildup that limits water intake by roots also becomes a problem. Hydroponic solutions perform the best in a pH range a little lower than for soil. The ideal pH range for hydroponics is from 5.8 to 6.8. Some gardeners run the pH at lower levels and report no problems with nutrient uptake. The pH of organic soil mixes is very important because it dictates the ability of specific pH-sensitive bacteria.

Measure the pH with a meter, monitor or waterproof tester (find our full selection here). When testing pH, take two or three samples and follow instructions supplied by the manufacturer. Soil test kits measure soil pH and primary nutrient content by mixing soil with a chemical solution and comparing the color of the solution to a chart. Most of these kits are difficult for novice gardeners to achieve accurate measurements. Comparing the color of the soil/chemical mix to the color of the chart is often confusing.

A measurement conversion chart is a useful tool for all hydroponic growers. It allows you to convert between common units of measure when testing your nutrient solution. Bluelab has a great chart.