EC Targets by Stage

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What EC actually measures

Electrical conductivity (EC) measures how well a solution conducts electricity, which scales with dissolved ionic salts — primarily the fertilizer ions you've added (nitrate, ammonium, potassium, calcium, magnesium, sulfate, phosphate) plus whatever was in your source water ^[1] Strong evidence.

EC is reported in millisiemens per centimeter (mS/cm) or microsiemens per centimeter (µS/cm). PPM (parts per million) is a conversion from EC using a scale factor — commonly 500 (NaCl/Hanna), 700 (KCl/European), or 640. The same solution reads as different PPM numbers on different meters, which is why serious growers quote EC, not PPM ^[2] Strong evidence.

EC tells you how much salt is in solution. It does not tell you which salts. A solution heavy in sodium from poor source water can read the same EC as a clean balanced feed, but the plant response is very different ^[1] Strong evidence.

Why growers use staged EC targets

Cannabis nutrient demand changes through its life. Seedlings have small root systems and are easily burned. Vegetative plants build leaf and stem mass and want more nitrogen and potassium. Flowering plants shift demand toward potassium and phosphorus and away from nitrogen. Matching feed strength to demand reduces two failure modes:

• Underfeeding: pale leaves, slow growth, premature senescence.
• Overfeeding (salt stress): tip burn, clawing, lockout, reduced water uptake, root damage ^[3] Strong evidence.

Staged EC targets are a practical heuristic for staying in the safe zone. They're not a yield-maximization protocol. Published EC schedules for cannabis come primarily from grower practice, commercial nutrient manufacturer guides, and adaptation of extension research from tomato and greenhouse vegetable production ^[4][5] Weak / limited. Controlled trials specifically optimizing EC schedules in cannabis are scarce.

Typical EC targets by stage

These ranges are widely used for soilless (coco, peat) and hydroponic systems, assuming reverse-osmosis or low-EC source water. Add your source water EC to these input targets if you're feeding tap.

These ranges derive from commercial nutrient guides and grower documentation ^[4][5] Weak / limited. No peer-reviewed consensus EC schedule exists for cannabis specifically. Treat the numbers as starting brackets, not fixed setpoints. Individual plants, light intensity, genetics, and root-zone temperature will shift the optimal point within or outside these ranges.

How to do it: step-by-step

1. Calibrate your meter. Use fresh two-point calibration solution (typically 1.413 mS/cm and either 0.0 or 12.88 mS/cm) every 1–2 weeks. An uncalibrated meter is worse than no meter Strong evidence.

2. Measure your source water EC. If it's above ~0.4 mS/cm, factor it into your input targets, or switch to reverse-osmosis. Hard tap water can push you over target before you add any nutrients.

3. Mix your nutrient solution to the input EC for the current stage. Add nutrients, stir, let temperature equilibrate to room temperature, then measure. Adjust pH after EC — pH adjusters change EC slightly but EC adjustments change pH significantly.

4. Feed and collect runoff. Aim for 10–20% runoff in coco and hydro to ensure you're feeding fresh solution and not recycling stale medium.

5. Read the runoff.

• Runoff EC ≈ input EC: plant is taking up water and nutrients in balance.
• Runoff EC > input EC (e.g., input 1.8, runoff 2.6): salts are accumulating in the medium. Lower input EC or increase runoff volume.
• Runoff EC < input EC: plant is eating faster than you're feeding, or the medium is buffering. Consider raising input EC slightly on the next feeding.

6. Watch the plant. Tip burn, clawed leaves, or dark glossy green foliage = reduce EC. Pale lower leaves with no other visible cause = increase EC. Visual symptoms are more reliable than any single meter reading Strong evidence.

7. Log everything. EC trends over time matter more than single readings. A simple spreadsheet showing input EC, runoff EC, and visual notes helps you see patterns and predict problems before they worsen.

Common mistakes

• Chasing a number instead of reading the plant. Two identical rooms with the same input EC can have wildly different outcomes due to light intensity, VPD (Vapor Pressure Deficit) Basics, root-zone temperature, and genetics. High-light rooms typically run higher EC because plants transpire and uptake more nutrients Weak / limited.
• Confusing PPM scales. A grower quoting "1000 ppm" on a 500-scale meter is at EC ~2.0; on a 700-scale meter that same EC reads ~1400 ppm. Always confirm the conversion scale ^[2] Strong evidence.
• Ignoring source water. Adding 1.6 mS/cm of nutrients to 0.6 mS/cm tap water gives a 2.2 mS/cm feed, not 1.6.
• Not calibrating regularly. Pen meters drift fast. Calibration solution is cheap insurance against false readings.
• Over-relying on runoff in organic or living soil. Runoff EC in actively amended soil reflects little about what's bioavailable to the plant. Meter readings tell you mostly about residual salts, not nutrient status.
• Over-flushing before harvest. Running plain water for weeks based on the belief it improves flavor or removes residuals is contested. Available evidence does not consistently support flushing as a quality-control measure Disputed.

Related techniques and interactions

• pH Management in Cannabis Cultivation — EC is meaningless without pH in the target range (5.5–6.5 for coco/hydro). Incorrect pH locks up nutrients even when EC is correct.
• VPD (Vapor Pressure Deficit) Basics and VPD by Growth Stage — Transpiration drives nutrient uptake. Higher VPD (drier air, warmer leaves) increases plant demand and water consumption, often requiring higher EC.
• PPFD Targets by Stage — Light intensity strongly influences nutrient demand and salt tolerance. Shadier gardens can run lower EC.
• Vegetative Stage Feeding — Details on nitrogen-rich ratios for veg growth.
• Coco Coir Growing — Coco-specific EC management and buffering properties.

Sources

How this page was made

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