Why measuring pH matters for healthy plants
If pH (potential of Hydrogen) is out of range, plant nutrient uptake drops, even with the right nutrients in your solution.
View pH tools
If pH (potential of Hydrogen) is out of range, plant nutrient uptake drops, even with the right nutrients in your solution.
View pH toolspH measures how acidic or basic your nutrient solution or growing media is. Crops perform best within a specific pH range; outside of it, nutrient availability and uptake can drop, even when nutrients are present. Regularly measuring and adjusting pH helps keep plants in the optimal up take zone and prevents common issues like nutrient lockout.
All plants need a balanced diet of nutrients (food) so that they can reach their full potential. pH (potential of Hydrogen) uses a 0-14 scale to determine the acidity (<7) or basicity (>7) of a sample with pH 7 being neutral.
When you take a pH measurement, the number you see is based on the concentration of hydrogen ions (H+). The more hydrogen ions the more acidic, the fewer the more alkaline.
Whether you’re looking for the best pH meter for hydroponics or need to test soil pH, we have a pH meter that will help you accurately measure your pH levels. Our products include handheld pH Pens, automated pH Controllers and wall-mounted Monitors.
| Grow Medium | Ideal Range |
|---|---|
| Hydroponics | 5.5 – 6.3 |
| Soil | 6.2 – 7.2 |
Check pH daily and whenever changes to nutrient solutions are made. When using soil and soilless media (peat, bark mixes, coco coir) test media pH using the pour-through method, soil slurry test, or direct measurement in the root zone bi-weekly or monthly. Testing frequency will depend on growing methods, plants, and critical factors such as changing fertilisers, deficiency symptoms, growth stages, etc.
pH is more critical in hydroponics than in soil because hydroponic systems lack the natural buffering capacity that soil provides. In soil, organic matter and microbial activity can help stabilise pH levels, making it less susceptible to fluctuations. In hydroponics, however, the nutrient solution is more directly influenced by the addition of fertilisers, which can cause rapid changes in pH. Maintaining the correct pH range (5.5-6.3) in hydroponics is essential for ensuring that nutrients remain soluble and available for plant uptake, preventing nutrient lockout and promoting optimal plant health. Regular monitoring and adjustment of pH are therefore crucial in hydroponic systems.
pH readings will drift in low-ionic-strength water like distilled, deionised, or RO. pH sensors rely on ions in the solution to produce a stable, reproducible reading, so pure water often gives erratic results even after calibration. CO2 absorption and small contamination can also shift the pH easily. To improve accuracy, measure a small sample, limit air exposure, keep the probe clean and hydrated, or add a small amount of calmag or high-purity KCl to increase ionic strength.
No two pH Probes behave exactly the same. This difference between the theoretical and actual behaviour of a pH Probe must be compensated for. A calibration is required to match the pH meter to the current characteristics of the pH Probe. These characteristics constantly change throughout a pH Probe's life, so, Bluelab recommends calibrating at least every 30 days. However, the more a pH Probe ages, the more frequent a calibration will be required.
Yes, temperature affects the actual pH of a solution, this is caused by changes in the dissociation constants of acids and bases. Meaning that the pH of a solution changes when temperature changes. During calibration, Bluelab meters use Automatic Temperature Compensation (ATC) to measure pH buffer temperature and add a correction factor to future pH readings. This reduces errors and eliminates the need to calibrate and test at the same temperature. ATC does not adjust the measured value of pH at different temperatures.
Clean your Bluelab pH Pen or pH Probe about once a month, or whenever readings look wrong, fluctuate, or an error appears, because salts and oils can build up and affect accuracy. Remove the cap correctly for your model, then swirl the probe tip in a small plastic container of clean tap water with a little Bluelab pH Probe Cleaner (or mild dishwashing liquid), rinse well under fresh running water, and if there’s heavy buildup, gently brush the glass bulb and junction with a soft toothbrush and a few drops of cleaner before rinsing again. Calibrate after every clean, then refit the cap and store the probe properly using the correct storage solution.
| Common crops | Optimal pH range |
|---|---|
| African Violet | 6.0 – 7.0 |
| Asparagus | 6.0 – 8.0 |
| Basil | 5.5 – 6.5 |
| Beans | 6.0 – 7.5 |
| Begonia | 5.5 – 7.5 |
| Blueberry | 4.5 – 5.5 |
| Broccoli | 6.5 – 7.5 |
| Brussel Sprouts | 6.0 – 7.5 |
| Cabbage | 6.0 – 7.5 |
| Carrot | 5.5 – 7.0 |
| Cauliflower | 5.5 – 7.5 |
| Celery | 6.0 – 7.0 |
| Chilis | 6.0 – 6.5 |
| Cucumber | 5.5 – 7.5 |
| Cyclamen | 6.0 – 7.0 |
| Eggplant | 5.5 – 7.0 |
| Geranium | 5.0 – 6.0 |
| Lettuce | 6.0 – 7.0 |
| Melon | 5.5 – 6.5 |
| Onion | 6.0 – 7.0 |
| Orchid | 4.5 – 5.5 |
| Pea | 6.0 – 7.0 |
| Pepper | 6.0 – 7.5 |
| Pumpkin | 5.5 – 7.5 |
| Spinach | 6.0 – 7.5 |
| Strawberries | 5.0 – 7.5 |
| Tomatoes | 5.5 – 6.5 |
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