I think I accidentally discovered “CO2 starvation” on my plant shelf and now I can’t unsee it. Has anyone else seen this?
I’ve got a dense shelf in a small room with the door usually closed, bright LEDs (roughly 400-600 PPFD at leaf level) running 12 hours. I added a cheap NDIR CO2 sensor for curiosity and noticed CO2 drops from 700 ppm (morning with open window) down to low 400s and sometimes 300-350 ppm after a few hours of lights-on. Right around that time my prayer plant and philodendrons get a weird midday slump that looks like overlight/underwater, but water and VPD are fine and they perk back up when I crack the window or run a fan that brings in fresh room air for a few minutes. When I scheduled the fan to kick on 5 minutes every hour, the midday droop basically vanished and new growth sped up.
Now I’m wondering if dense, well-lit indoor setups can actually go mildly CO2-limited without active air exchange, especially in small, sealed rooms. A few questions for the hive mind:
- Have you measured CO2 around a packed plant shelf or grow cabinet? What levels do you see over the photoperiod, and did plant behavior track the drops?
- Any clever, plant-safe ways to keep CO2 near ambient without wrecking humidity or temperature? Timed fresh-air bursts? A small duct bringing filtered air from another room? Midday light siesta to let CO2 rebound?
- Do certain houseplants seem more sensitive to dips (I’m seeing it most on Maranta, Pilea, and vining philos)?
- Sensor tips: placement, models that don’t drift like crazy, and how often you calibrate?
- Could this explain some cases of “mystery midday wilt under great lights” that aren’t water or heat issues?
I’m excited because this feels like a missing piece for indoor setups: we obsess over PPFD and humidity, but maybe light without fresh air hits a ceiling. Curious what others have seen and how you’ve solved it!