What is EC in Hydroponics?

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Heroic Hydro

6 min readDec 21, 2021

EC stands for Electrical Conductivity. The units for EC are millisiemens/cm (m/cm). You will also see microsiemens/cm (μ/cm). 1 m/cm equals 1000 μ/cm.

Hydroponic gardeners measure the EC of their nutrient solution in order to help them understand how much fertilizer is in it. EC measures the concentration of nutrients in your hydroponic fertilizer solution. This is because nutrients in many commercial hydroponic fertilizers are actually “nutrient salts”.

I have added an EC chart at the end of this post that you can use in order to figure out what EC is likely to be appropriate for your plant.

Buying an EC Probe

You can use a probe to measure EC. I use this 5 in 1 Apera probe that also does pH and other measurements. If this is too expensive, you could try this Apera probe that only measures EC or this vivosun probe.

What are Nutrient Salts?

Fertilizers commonly contain nutrient salts. We always think about plants as needing nitrogen, phosphorus, and potassium. In hydroponic fertilizer however, these nutrients are delivered in the form of salts because they break up into ions when dissolved in water. The plant is able to consume these ions. This makes nutrient salts ideal for hydroponics.

The Role of Ion Concentration in Plant Growth

For each stage of a plants life, there is an ideal concentration of ions in the hydroponic nutrient solution that supports growth. At a high level, the mass of ions inside and outside of the plant serves two purposes:

providing building blocks for tissue development related processes
attracting water into the the plant through Osmosis

Bigger plants must have more nutrients and must retain more water. Smaller plants require less nutrients and must retain less water. Osmosis is the process through which plants pull water into themselves.

The concentration of nutrient salt ions inside of the plant must be higher than outside of the plant in order for it to retain water. There must also be enough ions inside of the plant in order to maintain the tissue that it has as well as develop more of it.

What Happens if EC is Too High?

If the EC of the hydroponic nutrient solution is too high for your plant, the power of Osmosis reverses the water flow. Water will flow out of your plant rather than into your plant. Your plant will wilt and may die.

In general you should stick to the conservative side of what you think is appropriate for your plants, in order to maintain inward water flow.

How Do I Fix High EC?

Take out some of the nutrient solution and replace it with plain water. You should try to reach an EC level that is appropriate for your plants at their given size. At full size, Arugula, a leafy and delicate plant with thin stems, will take about 1 m/cm. A tall plant with thick stems, like Swiss Chard, will take ~2 m/cm or even more at full size. A big Tomato plan could take ~3 m/cm. Seedlings with their first set of leaves take ~ 0.3 m/cm. By the end of the third week of growth, when plants have 4–6 true leaves and are 2–3 inches tall, I aim for all of my plants to have a 0.8 m/cm nutrient solution.

What Happens if EC is Too Low?

Conservative EC is good, because it will always maintain a certain level of inward water flow. When EC is too low however, you may see soft, floppy, pale leaves. This is because the plant has grown too large for the current rate of inward water flow. It actually needs a higher rate of water flow now in order to carry out the processes of life. The sign that we see visibly with our eye-balls is that the intra-cellular pressure is too low, which causes the plant leaves to wilt.

How Do I Fix Low EC?

If you’re not sure what EC to give your plant, bump up the current EC by 0.1 m/cm, or check out the chart at the end of this post for guidance.

What If My Water Has High EC Already?

According to the WHO, water across the world averages 0.192 m/cm. My water fluctuates between 0.05 m/cm and 0.1 m/cm. If you have a water filter in your house, that will remove some salts.

Theoretically, the existing ion concentrating in your water will affect inward water flow, while at the same time those ions might or might not be consumable by your plants. In the worst case scenario, your water’s ion concentration will be high and the ions will not be consumable by the plants, meaning that you will have to maintain lower nutrient levels in order to maintain water flow, but your plants’ growth will be stunted.

With my water, I have never had a big problem like that. I allow for an additional 0.05 m/cm on top of the amount of m/cm that corresponds to plant nutrition. If I want to give my plants 1.0 m/cm, I add 0.05 m/cm to what I ultimately give my them, so 1.05 m/cm.

How Do I Measure EC?

You need a probe! Here is the Apera probe that I use. It also does pH, TDS, and PPM. TDS and PPM are other ways to understand the contents of your nutrient solution. I stick to EC and get really good results.

The All Purpose EC Chart

the day that the seeds go into the system: 0 m/cm

the day that the seeds germinate: 0 m/cm

the day that the seedlings start to sprout their 1st set of true leaves (not the first leaves that come out of the seed at the start of life, but the ones after that): 0.3 m/cm

The following EC values are relative to the day of the 1st set of leaves

day 7: 0.6 m/cm

day 14: 0.8 m/cm

day 21: 0.9 m/cm

From here on out, your plants’ growth will start to differentiate based on what kind of plant you’re growing. Big plants like Swiss Chard or Kale will have started to develop thicker stems and waxier leaves, whereas small leafy plants like mesclun mix or Arugula will stay small. The EC increases will reflect this.

See my article on how to test your plants to see if they need more nutrients.

Smaller Plant EC Schedule

Every week, aim for only a 0.1 m/cm increase or maybe even none at all. Refer to this article for more guidance.

Bigger Plant EC Schedule

Depending on the size and bulkiness of your plant, your weekly EC increases can get bigger and bigger and become more frequent.

Aim for 0.1 m/cm weekly increases at first. Eventually you may notice signs that your plant is ready for even more nutrients. Then you can go for 0.2 m/cm weekly increases or maybe even more. Refer to this article for further guidance.

Thanks for Reading!

Let me know if this article was useful!

When I started my journey with hydroponics I had SO many questions and it seemed like I couldn’t get satisfying answers anywhere. Most info online is either too general or too specific. So, I learned most of this stuff through trial and error.

Hopefully this article provides a comprehensive view of what EC is and you have a good starting place for feeding your plants the appropriate amount of nutrients.