CO2: When Enrichment Actually Pays
Why cannabis is CO2-limited at ambient, the 1,000–1,500 ppm target, the ~1,200 ppm sweet spot, and the hard rule that CO2 only pays above ~800–900 PPFD.
8 min read
Cannabis is a C3 plant, which means at ambient ~400 ppm CO2, the enzyme RuBisCO is CO2-limited and roughly 25–30% of captured energy is lost to photorespiration — the plant burns fixed carbon back off instead of building tissue. Enriching the air to 1,000–1,500 ppm raises the photosynthetic rate ~40–50% and delivers reported dry-bud gains of ~20–43%. But — and this is the entire lesson — only if light and temperature are elevated to match.
| Parameter | Veg | Flower (CO2-enriched) |
|---|---|---|
| CO2 (lights-on only) | 800–1,200 ppm | 1,000–1,500 ppm (≈1,200 optimal) |
| Air temp | 24–28 °C (75–82 °F) | 28–30 °C (82–86 °F) canopy |
| Paired PPFD | 400–600 | 1,000–1,500 |
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