Feeding for Real: EC and the Trend

What You Need to Know

Last lesson, pH decided whether food gets through the door. This lesson is about how much food to send — and the principle running through all of it is the one we’ve been building toward since Level 1: less is more. You can always add more. You can’t un-feed a plant.

The number that tells you how much food is in your water is EC — electrical conductivity. Dissolved nutrient salts conduct electricity, so the more nutrients in solution, the higher the EC reads. A higher EC means a stronger, more concentrated feed. That’s the whole concept: EC is a strength dial you can actually measure, instead of guessing from the cap on the bottle.

EC By Stage

Rough working bands — strain, medium and environment all shift them, so treat these as starting points, not commandments:

• Vegetative growth: EC 1.0–1.4. She’s building leaf and stem and eats steadily but not heavily. Start at the low end and let the plant earn the increases.
• Flowering: EC 1.4–2.0. Demand rises as buds form, but the ceiling is lower than the marketing on most bottles suggests.

Start every plant at half the label dose, watch for a week, and nudge up by 25% only if she’s clearly handling it — good colour, steady growth, no tip burn. The label is a guideline written for ideal conditions your tent doesn’t perfectly replicate, not a prescription.

The Trend Beats the Number

Here’s the part that turns a beginner into a grower: a single EC reading tells you very little. The trend in your runoff tells you almost everything.

Each feed, measure the EC going in and the EC coming out in the runoff. Then watch which way the runoff number moves over several feeds:

• Runoff EC climbing feed after feed: salts are accumulating in the root zone faster than the plant can use them. You’re overfeeding. The excess builds up, the EC in the root zone rises, and eventually it burns the leaf tips and starts locking nutrients out. Time to ease off and flush.
• Runoff EC falling well below input: the plant is eating everything you give it and could take a little more. Nudge the feed up.
• Runoff EC roughly tracking input: you’re in balance. Leave it alone.

One reading is a snapshot. The trend is the conversation.

When and Why to Flush

A flush is running a generous volume of plain pH’d water through the medium to wash out accumulated salts. You flush when the runoff EC has been climbing and the plant shows the strain — crispy tip burn, a rising root-zone EC, or symptoms that smell like salt lockout. It’s a reset, not a routine: flush when the trend tells you to, then resume feeding at reduced strength.

Seb’s Corner — the potassium the bottle oversells. A lot of “bloom booster” marketing leans on loading potassium into your flower feed. The evidence doesn’t back the hype. Bevan and colleagues (2021) ran a rigorous response-surface study on flowering cannabis in deep-water culture, varying nitrogen, phosphorus and potassium independently. Nitrogen and phosphorus drove yield — they found an optimal nitrogen around 194 mg/L and phosphorus around 59 mg/L, both with clear quadratic responses (too little hurts, too much hurts). Potassium, across a wide tested range of 60–340 mg/L, showed no significant effect on yield. Read that again: pushing K higher in flower, within normal ranges, didn’t buy more bud. So when you manage EC, you’re managing total dissolved salts — but the salts worth getting right are nitrogen and phosphorus. Chasing a high-K flower feed mostly buys you a higher EC, a faster salt buildup, and an earlier flush. We unpack this fully in the dedicated potassium-myth module; for now, let it stop you overspending your EC budget on the nutrient that doesn’t pay it back.

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How To Apply This

1. Get an EC/PPM meter and calibrate it like you do the pH pen. You measure feed strength the same way you measure pH — input and runoff.
2. Start at half label strength and at the low end of the stage band: EC 1.0 in early veg, building toward 1.4 as she fills out.
3. Measure input and runoff EC every feed and log both. The log is the point — it’s what makes the trend visible.
4. Read the trend over several feeds, not a single reading. Climbing runoff means back off; falling runoff means you’ve room to nudge up; matching means hold steady.
5. Flush when the trend and the plant agree there’s a salt buildup — generous plain pH’d water, then resume at reduced strength.
6. Spend your EC on N and P, not K. Don’t inflate your flower feed chasing potassium the plant won’t use. Run the numbers through the Nutrient Calculator rather than the bottle’s cap.

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Watch Out For

Feeding is where enthusiasm does the most damage.

The seven-bottle shelf. Base nutrients, CalMag, root stimulator, bloom booster, PK booster, carb supplement, microbial inoculant — all bought the same day, all used the same day, all at label dose. Tip burn within forty-eight hours. The plant needed the base nutrient at half strength and time. Add extras one at a time, with a reason you can name, once the base is dialled.

Treating EC as a target instead of a trend. A grower fixes on “hit 1.6” and feeds to that number regardless of what the runoff is doing. The runoff climbs, salts build, tips burn. The number going in matters far less than the direction the runoff is heading.

Flushing on a schedule. A flush is a reset for a specific problem — a salt buildup the trend has shown you. Flushing every week “to be safe” just disrupts a working root zone. Flush when the data calls for it.

Buying the high-K hype. The bloom booster promising massive potassium is selling you a higher EC and an earlier flush, not more yield. Put the budget into getting nitrogen and phosphorus right.

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Quiz

1. What does EC measure, and how does it relate to how strong your feed is?
2. Give the working EC band for the vegetative stage.
3. Your runoff EC has been climbing higher than your input for several feeds. What’s happening, and what does it call for?
4. According to Bevan et al. (2021), which two nutrients drove flowering yield, and what did they find about potassium?
5. Why is the trend in runoff EC more useful than any single EC reading?

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Sources

Bevan, L., Jones, M., & Zheng, Y. (2021). Optimisation of nitrogen, phosphorus, and potassium for soilless production of Cannabis sativa in the flowering stage using response surface analysis. Frontiers in Plant Science, 12, 764103. https://doi.org/10.3389/fpls.2021.764103. CC-BY 4.0. — optimal N (~194 mg/L) and P (~59 mg/L), and the finding that K had no significant yield effect across 60–340 mg/L.

Chapter 12, The Grower’s Guide (book draft) — EC bands by stage, half-strength feeding, runoff trend, and flush triggers. Ties into the GGB Nutrient Calculator and the potassium-myth module.

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Answer Key

1. EC measures electrical conductivity, which rises with the concentration of dissolved nutrient salts — so a higher EC means a stronger, more concentrated feed.
2. EC 1.0–1.4.
3. Salts are accumulating in the root zone faster than the plant uses them — you’re overfeeding. It calls for easing off the feed and, if the plant shows strain, a flush with plain pH’d water.
4. Nitrogen and phosphorus drove yield (optima around 194 mg/L N and 59 mg/L P). Potassium showed no significant effect on yield across the 60–340 mg/L range tested.
5. A single reading is a snapshot that can’t tell you whether the root zone is loading up or depleting; the trend across several feeds reveals the direction — climbing, falling, or steady — which is what actually tells you to back off, nudge up, or hold.

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Next lesson: Training I: Bend, Don’t Break — the plant’s fed and the air’s right; now we shape her, gently, so every bud site gets a fair share of the light you dialled in back at Lesson 2.1.