The pH level of a hydroponic nutrient solution dictates mineral availability (a plant’s ability to absorb essential nutrients). The quality of your water can have a huge impact on your garden. pH is the measure of how acidic or basic your water is. The basic scale range runs from 0 to 14, designating 7 as neutral. Below 7 is acidic and above 7 is basic or alkaline. Treated city water typically ranges from 6.5-7.5 and will need to be lowered. The ideal range for most plants is 5.5 to 6.5. When pH falls outside this window, essential elements bind together or drop out of the solution, causing nutrient lockout, slow growth, and/or root damage.
A simple color test is sufficient for small gardens. Using a Soil pH Test Kit (found on Amazon), follow the directions on the color card and test your water before adding nutrients as well as after. Compare the colors to the chart and adjust pH accordingly. After testing a few times, you will get an idea of what you will need to adjust your pH each time you add your water and nutrients.
An example of how to adjust this as follows: If the pH of the water is 7.0 or lower do not add acid. Mix the fertilizer as directed and run a cycle of fertilizer and check the pH at the emitters. If the pH is 7.6 or higher then add
Ideal pH Range
- Most crops (herbs, lettuce, tomatoes) thrive at a slight acid level of 5.5 to 6.5.
- A tighter sweet spot for maximum nutrient uptake is 5.8 to 6.2.
Effects of High pH (Above 6.5)
- Nutrient Lockout: Iron, manganese, boron, copper, and zinc become hard for roots to absorb.
- Plant Symptoms: New leaves turn yellow between the veins (iron deficiency), tips burn, and overall plant growth slows.
Effects of Low pH (Below 5.5)
- Nutrient Lockout: Calcium, magnesium, and phosphorus become unavailable to the plant.
- Root Toxicity: High amounts of free aluminum, iron, and copper become overly soluble, which can burn and damage root tissues.
- Plant Symptoms: Stunted roots, dark green older leaves with dead spots, and blossom end rot on fruiting plants.
Ideal pH Ranges for Common Hydroponic Plants
- Lettuce & Leafy Greens: 5.5 – 6.5
- Tomatoes: 5.5 – 6.5
- Cucumbers: 5.8 – 6.0
- Peppers (Bell & Hot): 6.0 – 6.5
- Strawberries: 5.0 – 5.5
- Basil & Herbs: 5.5 – 6.5
- Spinach: 5.5 – 6.6
Available Household Options
Natural Low pH Options
Citric Acid: A powder or liquid squeezed from citrus fruits that lowers pH quickly, but microbes and plants consume the citrate ions, causing the pH to rise again within 24 hours. To lower pH add citric acid - 1 tbsp per gallon, mix until dissolved test again. Test again the next day adjust as needed by tbsp.
Natural High pH Options 7.6 or Higher
Vinegar: To raise pH, add 1oz of vinegar per gallon, mix well and test again...then test the next day and adjust as needed in 1oz increments.
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