PPM (Parts Per Million) in Cannabis Growing
PPM, or Parts Per Million, is a measurement used to estimate the concentration of dissolved nutrients in water or nutrient solutions. In cannabis growing, PPM is commonly used to gauge feeding strength and monitor runoff.
PPM is a converted value, not a direct measurement.
What Does PPM Tell Growers?
PPM helps growers estimate:
- Overall nutrient concentration
- Whether plants are being underfed or overfed
- Changes in nutrient uptake over time
- Potential salt buildup in the growing medium
Higher PPM values indicate more dissolved solids in the solution.
PPM and Nutrient Feeding
PPM reflects total dissolved solids, not specific nutrients.
Different nutrient formulas can produce the same PPM while delivering very different nutrient ratios. PPM should be used as a general guide rather than a precise feeding rule.
PPM and Autoflower Cannabis
Autoflowers typically respond best to:
- Lower PPM ranges than photoperiod plants
- Gradual increases as plants mature
- Consistent feeding rather than aggressive spikes
Overfeeding at high PPM levels can quickly stress autoflowers.
PPM Scales and Confusion
PPM readings depend on conversion scales:
- 500 scale
- 700 scale
The same solution can show different PPM values depending on the meter. This is why EC is often preferred for consistency.
How PPM Is Measured
PPM is measured by:
- Using digital TDS or combo meters
- Testing nutrient solutions (input)
- Testing runoff (output)
Comparing input and runoff PPM can help diagnose root zone issues.
Common PPM Mistakes
- Mixing PPM targets from different scales
- Feeding solely based on numbers
- Ignoring plant response
- Applying photoperiod feeding charts to autoflowers
Plants should always guide feeding decisions.
Quick Summary
- PPM estimates nutrient concentration
- Converted from EC measurements
- Useful for monitoring feeding strength
- Autoflowers prefer lower PPM ranges
- Best used alongside visual plant cues