What Is EC?
EC stands for Electrical Conductivity — a measure of how many dissolved salts (nutrients) are in your water. Pure water barely conducts electricity; the more nutrient salts you add, the better it conducts. EC is measured in mS/cm (millisiemens per centimeter).
In practice, EC answers one question: how strong is this feed? Two growers can use completely different nutrient brands, but if both mix to EC 1.4, their plants receive a comparable overall salt load. That is why EC — not milliliters per liter from a bottle label — is the number worth tracking.
EC vs. ppm — the Conversion Trap
Some meters display ppm (parts per million) instead of EC. The catch: there are two competing conversion scales, and meters don't always tell you which one they use.
| EC (mS/cm) | ppm — 500 scale (US, TDS) | ppm — 700 scale (EU/AU) |
|---|---|---|
| 0.5 | 250 | 350 |
| 1.0 | 500 | 700 |
| 1.5 | 750 | 1050 |
| 2.0 | 1000 | 1400 |
Recommendation: Work in EC directly. It is scale-free, every serious feeding chart uses it, and GrowVPD Pro displays all targets in mS/cm.
Target EC by Growth Stage
Feed strength ramps up from a gentle seedling feed to a peak in mid-flower, then tapers off and ends with a plain-water flush. These are the baseline targets for coco and hydro (direct fertigation):
| Stage | Coco / Hydro (mS/cm) | Soil (mS/cm) |
|---|---|---|
| Seedling / Clone | 0.4 – 0.8 | 0.3 – 0.6 |
| Early Veg | 0.8 – 1.2 | 0.6 – 0.8 |
| Late Veg | 1.2 – 1.6 | 0.8 – 1.1 |
| Pre-Flower | 1.4 – 1.8 | 1.0 – 1.3 |
| Early & Mid Flower | 1.6 – 2.0 | 1.1 – 1.4 |
| Late Flower | 1.4 – 1.8 | 1.0 – 1.3 |
| Flush | 0.0 – 0.4 | 0.0 – 0.3 |
Why is the soil column ~30% lower? Because soil already holds and releases nutrients on its own. Feeding soil at full coco strength stacks salt on top of what the substrate provides, which is the fastest route to nutrient burn.
Living soil is the exception: a living / super-soil bed is fed by top-dressing and its biology self-regulates pH and availability. Don't chase EC or pH numbers in the watering can — water plain, feed the soil, and let the microbes do the chemistry. GrowVPD Pro deliberately hides pH/EC targets for living-soil grows.
pH Belongs to the Medium, Not the Bottle
EC says how strong the feed is; pH decides whether the plant can actually absorb it. The correct pH window depends on your medium:
| Medium | Target pH | Note |
|---|---|---|
| Soil | 6.0 – 6.8 | Soil buffers — small drift is fine. |
| Coco (veg) | 5.8 – 6.0 | The classic coco sweet spot. |
| Coco (flower) | 6.0 – 6.2 | Riding the top of the window improves P/Ca availability late. |
| Hydro / DWC | 5.5 – 6.0 | Let it drift within the window — a slow sweep is healthy. |
| Living soil | — | Self-regulating; don't adjust the water. |
When you lower pH, the acid you choose matters too: nitric acid adds nitrogen (a fit for veg), phosphoric acid adds phosphorus (a fit for flower). Citric acid is unstable in reservoirs — microbes eat it within hours. The GrowVPD Pro nutrient calculator shows how many ppm of N or P your pH-down dose actually adds.
Measure Input AND Runoff
Input EC tells you what you gave; runoff EC tells you what is happening in the pot. Collect the last bit of runoff and compare:
- Runoff ≈ input (±0.3): healthy balance — the plant is eating roughly what you feed.
- Runoff much higher than input (+0.5 or more): salt is accumulating in the substrate. Back off feed strength or give a plain-water irrigation with ~20% runoff to reset.
- Runoff lower than input: the plant is consuming aggressively — it can usually handle a slightly stronger feed.
Adjusting EC in Practice
EC Too High (tip burn, dark clawing leaves)
- Dilute the reservoir with plain water to target.
- Irrigate to generous runoff to wash accumulated salt out of the root zone.
- Rebuild the feed ~0.2 mS/cm below the old level and watch runoff.
EC Too Low (pale, slow, hungry plants)
- Step feed strength up in ~0.2 mS/cm increments, not big jumps.
- Verify your base water first: tap water often starts at 0.2–0.5 EC that contributes no useful nutrition.
How GrowVPD Pro Puts This on Autopilot
- Grow templates show a pH · EC chip for every week — values written by the template author always win; otherwise they derive from your week's position in the schedule.
- Feeding plans display the full target line per week: pH · EC · °C · %RH · VPD · PPFD.
- The diary logs your measured pH/EC next to the target, so drift is visible week over week.
- The nutrient calculator converts your pH-down dose into real added N/P ppm.