pH & EC: The Complete Guide
Master the key measurements for healthy plants. Learn optimal ranges for soil, hydroponics, and greenhouse — and when to adjust.
Optimal pH Range
5.5 - 6.5
For most hydroponic plants
Typical EC Range
1.0 - 2.5
Varies by plant and stage
What is pH?
pH measures how acidic or alkaline a solution is, on a scale of 0-14. In hydroponics, pH determines which nutrients your plants can actually absorb.
Optimal pH by Plant Type
While most plants thrive in 5.5-6.5, some have specific preferences:
| Plant | pH Range | Optimal |
|---|---|---|
| Most vegetables | 5.5 - 6.5 | 6.0 |
| Leafy greens | 5.5 - 6.5 | 6.0 |
| Herbs | 5.5 - 6.5 | 6.0 |
| Tomatoes | 5.5 - 6.5 | 6.0 |
| Strawberries | 5.5 - 6.2 | 5.8 |
| Peppers | 5.5 - 6.5 | 6.0 |
| Blueberries | 4.5 - 5.5 | 5.0 |
| Cannabis | 5.5 - 6.5 | 6.0 |
Adjusting pH
pH naturally drifts over time - usually upward as plants consume acidic nutrients. Here's how to correct it:
Use pH Down (phosphoric acid)
- • Add a few drops at a time
- • Stir and wait 15 minutes
- • Re-test before adding more
- • A little goes a long way!
Use pH Up (potassium hydroxide)
- • Add a few drops at a time
- • Mix thoroughly
- • Wait and re-test
- • Less common issue
What is EC?
EC (Electrical Conductivity) measures how many dissolved salts (nutrients) are in your solution. Higher EC = more nutrients. It's measured in mS/cm (millisiemens per centimeter).
You might also see TDS (Total Dissolved Solids) in ppm. To convert: EC × 500 = TDS (ppm)
0.5-1.0
Seedlings
Light feeding
1.2-2.0
Vegetative
Standard feeding
1.8-2.5
Flowering
Heavy feeding
Optimal EC by Plant Type
| Plant | EC Range | Notes |
|---|---|---|
| Lettuce | 0.8 - 1.2 | All stages |
| Basil | 1.0 - 1.6 | All stages |
| Tomatoes | 2.0 - 5.0 | Fruiting |
| Peppers | 1.8 - 2.8 | Fruiting |
| Strawberries | 1.0 - 1.4 | Fruiting |
| Cannabis | 1.2 - 2.4 | Varies by stage |
| Cucumbers | 1.7 - 2.5 | Fruiting |
Measurement Equipment
Accurate measurements require decent equipment. Here's what to look for:
- ✓ Digital pen-style is easiest
- ✓ ATC (Auto Temperature Compensation)
- ✓ Budget: $15-50 works fine
- ✓ Calibrate weekly with buffer solutions
Popular: Apera pH20, Bluelab pH Pen
- ✓ Digital pen-style
- ✓ ATC built-in
- ✓ EC or TDS (or both)
- ✓ Budget: $15-40
Popular: HM Digital, Bluelab Truncheon
Daily Monitoring Routine
- 1
Check pH first thing
Same time daily for consistency
- 2
Record the reading
Track trends over time
- 3
Check EC
Note if rising or falling
- 4
Adjust if needed
pH outside 5.5-6.5? Add pH Up/Down
- 5
Top up reservoir
Use pH-adjusted water
- 6
Check water level
Never let roots dry out
Track Your Plants
Use Truleaf's plant diary to log pH and EC readings, track trends, and catch problems early.