Why Your Plant Can Starve in a Pot Full of Food: pH and EC, Explained

You fed your plant on schedule. The bottle promised everything it needs: nitrogen, phosphorus, potassium, calcium, magnesium. And yet the new leaves are coming in pale, the older ones are spotting, and the whole plant looks hungry. Adding more food seems like the obvious fix. Often, it makes things worse.

The problem usually isn’t what’s in the pot. It’s whether the roots can get to it. Two numbers decide that: pH and EC.

pH: The Lock on the Pantry

pH measures how acidic or alkaline the water around the roots is, on a scale from 0 to 14. It matters because every nutrient is only easy to absorb inside a certain pH range. Push the pH too high and iron and manganese become hard to take up. Let it drop too low and calcium and magnesium suffer. Outside the sweet spot, the nutrients are still sitting in the medium, but in a form the roots can’t use. Growers call this nutrient lockout.

In soil, most growers aim for a pH of roughly 6.0 to 7.0. In soilless media like coco coir, the usual target is lower, around 5.8 to 6.2. Small swings inside that window are normal, and even helpful, because different nutrients are easiest to absorb at slightly different points. Big, lasting drift is what causes trouble.

The tricky part is that lockout looks exactly like a deficiency. The grower sees yellowing, adds more nutrients, and pushes the root zone even further out of balance.

EC: How Much Food Is in the Water

EC (electrical conductivity) measures how much dissolved fertilizer is in the water. Pure water barely conducts electricity. The more nutrient salts you dissolve in it, the higher the reading.

Too low, and the plant goes hungry. Too high, and the root zone gets so salty that it starts pulling water away from the roots instead of letting them drink. The first sign is usually burnt, crispy leaf tips. A seedling needs a very light feed, while a plant in full flower can handle far more. There’s no single right EC, only the right EC for this plant at this stage.

Why the Runoff Tells the Real Story

Here’s what most first-time growers miss: measuring what goes into the pot only tells you half the story. The water that drains out of the bottom, the runoff, has passed through the roots and the medium. It carries a report of what happened down there.

Compare the runoff with the feed, and patterns start to appear:

1. Runoff EC well above the feed. The plant is drinking water faster than it uses nutrients, and salts are building up in the medium.
2. Runoff EC well below the feed. The plant is feeding hungrily and may want a stronger mix.
3. Runoff pH far from the feed pH. The root zone has drifted, and lockout may be on its way.

Commercial growers check this routinely. At home, it usually means pen meters, calibration fluids, a notebook and doing the math yourself, which is exactly why most hobby growers skip it until something goes wrong.

How We Solved It for Sunday

When we designed Sunday alongside expert growers, we wanted pH and EC off the owner’s to-do list entirely. Sunday mixes every irrigation batch itself, in a dedicated mixing tank, automatically dosing nutrients and adjusting pH and EC to your plant’s current stage. You never mix anything. You just pour fresh water into the water tank.

Sunday measures pH and EC with its own wireless pH & EC sensor, so the mix is checked, not guessed. And because Sunday is a drain-to-waste system, the excess water from every irrigation drains into a separate runoff container, so old water never goes back to the roots. That gave us the chance to close the loop. If you want to squeeze even more out of your plant, you can also use the sensor to measure the runoff and fine-tune the mix to what your plant is actually absorbing. It’s optional, and it’s the same feedback commercial growers use to push their yields, without the notebook.

Sensors drift over time, so we made calibration simple too. Your first grow kit includes pH and EC calibration solutions, the sensor is wireless, so it’s easy to calibrate, and every so often the app asks you to recalibrate and walks you through each step.

The Takeaway

If your plant looks hungry, don’t reach for the nutrient bottle first. Check the pH, check the EC and, if you can, check the runoff. More often than not, the answer is already in there.