Hydroponic Plant Library: pH and EC Starting Points
This 12-crop library separates source-backed nutrient-solution ranges from fields that require cultivar-, growth-stage-, and system-specific validation. A blank or “source required” field is intentional: it prevents a generic number from being presented as an exact production target.
12-crop data matrix
| Crop | EC (mS/cm) | pH | Climate and stage note | Data status |
|---|---|---|---|---|
| Lettuce | 1.2-1.8 | 6.0-7.0 | Cool leafy crop; crop-stage temperature, water temperature, RH, VPD, PPFD and DLI require the selected lettuce system or cultivar source | EC/pH: OSU Extension |
| Basil | 1.0-1.6 | 5.5-6.0 | Warm herb; Penn State notes basil should not be kept below 50 F and gives general indoor-herb day/night guidance | EC/pH: OSU; climate context: Penn State |
| Cilantro | Crop-specific program required | Validate in system | Indoor-herb guidance is available, but no universal hydroponic EC/pH target is asserted here | Open field - do not copy another herb |
| Mint | Crop-specific program required | Validate in system | Indoor-herb guidance is available, but no universal hydroponic EC/pH target is asserted here | Open field - do not copy another herb |
| Kale | Crop-specific program required | Validate in system | Cool leafy crop; use the exact cultivar, fertilizer and production-system source | Open field - do not substitute cabbage values |
| Spinach | 1.8-2.3 | 6.0-7.0 | Cool leafy crop; refer to the Cornell CEA spinach resources for system design | EC/pH: OSU |
| Bok choy / Pak choi | 1.5-2.0 | 7.0 | Leafy brassica; cultivar and production system determine climate and light targets | EC/pH: OSU |
| Tomato | 2.0-4.0 | 6.0-6.5 | Fruiting crop; stage-specific EC, VPD and light targets must come from the selected greenhouse program | EC/pH: OSU |
| Pepper | 0.8-1.8 | 5.5-6.0 | Fruiting crop; cultivar and stage materially affect nutrient and climate targets | EC/pH: OSU |
| Cucumber | 1.7-2.0 | 5.0-5.5 | Fruiting vine; confirm climate, VPD, light and irrigation targets for the actual cultivar | EC/pH: OSU |
| Strawberry | 1.8-2.2 | 6.0 | Fruiting crop; propagation and production stages require different environmental programs | EC/pH: OSU |
| Microgreens | Varies by crop and harvest stage | Validate in system | “Microgreens” includes many species; use the seed, substrate and food-safety program for the exact crop | No universal target published |
Required profile fields
For every crop and growth stage, record: cultivar, propagation method, system type, fertilizer formula, source-water pH/EC/alkalinity, target pH, target EC, water temperature, air day/night temperature, RH, VPD, PPFD, photoperiod, DLI, CO2 practice, alarm limits, corrective action, source, reviewer and review date.
Action logic
- Unexpected pH: verify the probe, mixing, temperature, source water and alkalinity before adding an adjuster. OSU notes that high alkalinity can drive pH upward.
- Unexpected EC: verify units, source-water EC, reservoir volume, fertilizer mixing and plant stage. EC represents total ionic conductivity, not every nutrient concentration.
- TDS mismatch: compare EC first and confirm the conversion factor used by each instrument.
- Temperature or VPD alarm: confirm sensor height, airflow, direct radiation, humidifier or heater discharge, and crop-stage source before changing the environment.
- Food safety: sensor readings do not replace sanitation, source-water safety, crop handling or microbial controls.
Sources
- Oklahoma State University Extension - Electrical Conductivity and pH Guide for Hydroponics
- University of Minnesota Extension - Small-scale hydroponics
- Cornell Controlled Environment Agriculture - Greens resources
- Penn State Extension - Growing Herbs Indoors
- Purdue Extension - Microgreens
Database version 2.0. Reviewed August 1, 2026. EC/pH numbers are source-backed; unverified crop-stage fields remain explicitly open rather than estimated.