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EC meter for plants: how to measure fertiliser levels
An EC meter for plants tells you how much nutrient salt is in the soil or water. Here you’ll find the right EC for hydroponics and potting mix, how to measure accurately, and how to spot too much or too little fertiliser.
What does an EC meter for plants measure?
EC stands for electrical conductivity. Dissolved salts, such as nutrient salts from fertiliser, conduct electricity: the more salts, the higher the EC. So by measuring EC, you know how much nutrient is in the soil or water. However, an EC meter does not tell you which nutrient it is; for that you need an NPK test (USDA NRCS).
EC is usually given in mS/cm (millisiemens per centimetre). 1.0 mS/cm equals 1000 µS/cm and 1.0 dS/m (UMass Amherst). Some meters show ppm or TDS. That is a conversion of EC with a factor of 500 or 700, so EC 1.0 is 500 or 700 ppm, depending on the scale (Bluelab).
EC chart: hydroponics by crop
| Crop | EC (mS/cm) | pH |
|---|---|---|
| Tomato | 2.0 – 4.0 | 6.0 – 6.5 |
| Lettuce | 1.2 – 1.8 | 6.0 – 7.0 |
| Pepper | 0.8 – 1.8 | 5.5 – 6.0 |
| Cucumber | 1.7 – 2.0 | 5.0 – 5.5 |
EC of potting mix and garden soil
| What | Normal | Too high | Source |
|---|---|---|---|
| Potting mix, pour-through method | 2.6 – 4.6 | from 4.6 | UMass Amherst |
| Potting mix, 1:2 method (mix:water) | 0.76 – 1.25 | from 1.26 | UMass Amherst |
| Garden soil (saturated extract) | below 2.0 = non-saline | from 4 = saline | USDA NRCS |
If you use an EC meter for plants directly in the soil, the reading also depends on how wet and how warm the soil is. Wetter soil gives a higher EC, and EC drops by about 2 percent per degree colder (USDA NRCS). So measure at similar soil moisture and mainly watch the trend: does EC rise after each feed, or fall away?
How to use an EC meter for plants in 4 steps
- Calibrate the meter. Use calibration solution of 1.41 mS/cm (1413 µS/cm), stir and wait until the reading is stable (Oklahoma State University).
- Keep conditions the same. Always measure soil at about the same moisture, for example one day after watering. Also read how to measure soil moisture.
- Measure at root depth. Push the meter into the soil to where the roots are, or hold the EC meter in the water or nutrient solution. Measure in several spots and take the average.
- Write it down and compare. In hydroponics, measure every day at the same time, EC first and pH second (Oklahoma State University). For pot plants, measure before and after feeding to see what the fertiliser does.
EC meter for plants, NPK test kit or laboratory?
| EC meter | NPK test kit | Laboratory | |
|---|---|---|---|
| What it measures | Total nutrient salts | Nitrogen, phosphorus, potassium (and pH) | Each nutrient separately |
| Speed | Instant | Within an hour | Days to weeks |
| Accuracy | Good for trends, after calibration | Indication: low, medium, high | Most accurate, with fertiliser advice |
| Best for | Hydroponics, pot plants, tracking | Vegetable garden and lawn, what is missing | Large garden, doubts, liming advice |
| Example | EC soil meter, EC meter for liquids | Soil test kit N, P, K, pH | – |
An EC meter for plants is ideal for tracking whether there is enough nutrient in the soil or water. If you want to know which nutrient is missing, you need an NPK test. A soil test kit or the 10-in-1 soil tester quickly gives you a picture per nutrient. For full fertiliser advice, have the soil tested by a laboratory.
Spotting too much or too little fertiliser with an EC meter for plants
Too much fertiliser (EC too high)
With too much fertiliser you see brown roots and leaf tips, wilting, misshapen leaves and a white crust on the pot rim (University of Connecticut). In addition, a high EC can cause root injury, yellowing leaves and leaf margin burn (UMass Amherst). Flush the pot thoroughly with plenty of free-draining water, or repot into fresh potting mix (University of Connecticut). After that, feed less often and at a lower concentration (UMass Amherst).
Too little fertiliser (EC too low)
A low EC usually means a nutrient shortage and slower growth (Oklahoma State University). Feed a little more often or slightly stronger, and check again with your EC meter after a week.
When to fertilise?
Feed houseplants while they are growing, usually from March to October. In winter they hardly grow, so skip feeding then. A diluted dose more often is better than a full dose once a month, because it gives a steadier supply (University of Connecticut).
Our picks: EC meter for plants and nutrient testers
Frequently asked questions: EC meter for plants
Understanding EC
What is EC in plants?
EC stands for electrical conductivity. It shows how many dissolved salts, such as nutrient salts from fertiliser, are in the soil or water. The more salts, the higher the EC (USDA NRCS).
What is the difference between EC and ppm?
EC is the measured conductivity in mS/cm. Ppm or TDS is a conversion of it, with a factor of 500 or 700. EC 1.0 mS/cm is 500 ppm on the 500 scale or 700 ppm on the 700 scale (Bluelab). Preferably use EC, so you don’t need to know which scale your meter uses.
Does an EC meter show which nutrients are in the soil?
No. An EC meter measures total dissolved salts, not which nutrient it is (USDA NRCS). To find out whether nitrogen, phosphorus or potassium is missing, use an NPK test or have the soil tested by a laboratory.
What are the signs of over-fertilising plants?
Brown leaf tips and roots, wilting, misshapen leaves and a white crust on the pot rim (University of Connecticut). Yellowing leaves and leaf margin burn can also point to a high EC (UMass Amherst).
Right EC values
What is the ideal EC for hydroponics?
It depends on the crop. Lettuce does well at 1.2 to 1.8 mS/cm, pepper at 0.8 to 1.8, cucumber at 1.7 to 2.0 and tomato at 2.0 to 4.0 (Oklahoma State University).
What is a good EC for potting mix?
It depends on the test method. With the pour-through method 2.6 to 4.6 mS/cm is normal, with the 1:2 method 0.76 to 1.25 mS/cm (UMass Amherst). If you use a probe meter, mainly watch the trend after feeding.
What soil EC is too high?
Garden soil with an EC below 2 dS/m (equal to 2 mS/cm, measured in saturated extract) is non-saline. From 4 dS/m the soil is saline, and plants struggle to take up water (USDA NRCS).
Measuring and feeding
How do you calibrate an EC meter?
Hold the meter in calibration solution of 1.41 mS/cm (1413 µS/cm), stir and wait until the reading is stable. Then set the meter to this value (Oklahoma State University).
How do you fix over-fertilised plants?
Flush the pot thoroughly with plenty of free-draining water, or repot into fresh potting mix (University of Connecticut). After that, feed less often and at a lower concentration (UMass Amherst).
When should you fertilise houseplants?
While they are growing, usually from March to October. Don’t feed in winter. A diluted dose more often is better than a full dose once a month (University of Connecticut).
Measuring acidity too? Read how to test soil pH and how to test the pH of water. Read more about the EC of water and an NPK soil test. You can find the manuals for our meters under download manuals.
Not sure which meter suits you?
Tell us what you want to measure: pot plants, vegetable garden or hydroponics. We’ll help you choose the right EC meter or test kit, free of charge.
Sources
- Singh & Dunn, Electrical Conductivity and pH Guide for Hydroponics, Oklahoma State University: EC and pH by crop in hydroponics, adjusting EC
- Soluble Salts / Electrical Conductivity (EC) for Greenhouse Crops, UMass Amherst: EC standards for potting mix and soil by test method, symptoms
- Soil Electrical Conductivity, Soil Quality Indicators, USDA NRCS: what EC in soil tells you and what affects it
- Pettinelli, Fertilizing Houseplants, University of Connecticut: when to fertilise, signs of over-fertilising
- Soil test kits vs. laboratory tests (2019), Montana State University: test kits compared with the laboratory
- Bluelab, What are the different conductivity scales?: converting EC to ppm
Last updated: 9 November 2026