Check and Adjust pH
Lesson 7 of 14
pH tells you how acidic the solution is. It controls whether the plant can actually absorb the nutrients you just mixed in, so it is worth two minutes of checking.
The range to aim for
UF/IFAS recommends a pH of about 5.5 to 6.0 for Kratky growing. Oklahoma State University Extension lists crop ranges that mostly fall between 5.5 and 6.5. Aim for 5.5 to 6.0 and you will suit almost every beginner crop.
Why it matters
Nutrients are most available to plants in this slightly acidic range (Oklahoma State University Extension). When pH runs high, iron and other micronutrients become harder to absorb, and the newest leaves turn pale (Greenhouse Grower, with Neil Mattson).
How to test
- Test strips: dip and compare the color with the chart.
- Liquid drops: add drops to a small sample and compare. Often easier to read than strips.
- A pH meter: the most precise, but it needs calibrating with buffer solutions.
Adjusting
- Always adjust pH after the nutrients are mixed in, because nutrients change pH (Oklahoma State University Extension).
- To lower pH, add pH down a few drops at a time. White vinegar also works; UF/IFAS notes it typically takes around 2 teaspoons per gallon, depending on your water.
- Stir, wait a few minutes and test again.
- If you go too low, raise it with a very small amount of pH up.
Do you need to keep checking?
In a well-mixed Kratky container you rarely need to adjust pH again (UF/IFAS). Check it at mixing time, and again only if the plant shows a problem.
Your task for this lesson
Practise once with plain tap water: test it, add a little pH down, and test again. Then you will know how your water behaves before the real batch.
Sources
- University of Florida IFAS Extension. Set It and Forget It Hydroponics (HS1488).
- Dunn, B. and Singh, H. Oklahoma State University Extension. Electrical Conductivity and pH Guide for Hydroponics (HLA-6722).
- Greenhouse Grower, with Neil Mattson (Cornell University). Tips to Avoid Nutrient Issues in Greenhouse Lettuce.