GrowAI tracks every environmental variable your cannabis plants depend on — VPD, temperature, humidity, CO₂, pH, EC, and DLI — in real time, by growth stage, with AI diagnosis and automated alerts.
Launching April 20, 2026 — 4/20
Vapour Pressure Deficit (VPD) is the single most important environmental metric for cannabis cultivation. VPD describes the difference between the amount of moisture the air can hold and how much it currently holds — essentially, how hard the air is pulling moisture from your plants' leaves.
Too low a VPD (high humidity, low temperature) slows transpiration and nutrient uptake, encourages mould, and causes soft, weak growth. Too high a VPD (low humidity, high temperature) stresses the plant, causes stomata to close, halts photosynthesis, and burns yield potential. Getting VPD dialled in by stage is the single biggest lever most home cannabis growers aren't pulling.
| Growth Stage | VPD Target (kPa) | Temp (°F) | RH % | Notes |
|---|---|---|---|---|
| Seedling (Days 1–7) | 0.4 – 0.8 | 72–78°F | 65–80% | Roots not established — plant absorbs water through leaves. High RH critical. |
| Clone / Propagation | 0.4 – 0.8 | 72–78°F | 70–80% | Under dome or humidity tent until roots form. Mist leaves twice daily. |
| Early Veg (Week 1–2) | 0.8 – 1.0 | 72–82°F | 55–70% | Begin ramping VPD as root zone develops. Increase EC gradually. |
| Late Veg (Week 3–5) | 0.9 – 1.2 | 74–84°F | 50–65% | Full veg range. Push temperatures for faster growth if RH allows. |
| Early Flower (Week 1–4) | 1.0 – 1.3 | 72–80°F | 45–60% | Drop RH gradually as buds develop. Begin lowering lights-off temp delta. |
| Late Flower (Week 5–harvest) | 1.2 – 1.5 | 68–78°F | 40–50% | Low RH critical to prevent bud rot. Keep below 1.6 to avoid stress. |
| Flush / Pre-Harvest | 1.0 – 1.4 | 65–75°F | 40–50% | Reduce EC to 0.0–0.4 mS/cm. Drop night temps 10°F to enhance colour. |
GrowAI calculates VPD live from your temperature and humidity sensors and displays it on your dashboard alongside the target range for your plant's current growth stage. When VPD drifts outside the target window, you get an instant alert — day or night.
pH and EC are the two most frequent causes of cannabis problems. pH outside the optimal window causes nutrient lockout — plants show deficiency symptoms even when nutrients are present in the reservoir. EC too high causes nutrient burn and salt buildup; too low causes deficiencies and slow growth.
| Stage | pH (Hydro/Coco) | pH (Soil) | EC Target (mS/cm) | Notes |
|---|---|---|---|---|
| Seedling | 5.8 – 6.0 | 6.0 – 6.5 | 0.4 – 0.8 | Plain water or very weak nutrient solution. Avoid overfeeding seedlings. |
| Clone | 5.8 – 6.0 | 6.0 – 6.5 | 0.6 – 1.0 | Cloning gel on cutting. No heavy nutrients until roots visible. |
| Early Veg | 5.8 – 6.2 | 6.0 – 6.8 | 1.0 – 1.4 | Begin nitrogen-heavy grow formula. Increase EC as leaves multiply. |
| Late Veg | 5.8 – 6.2 | 6.0 – 6.8 | 1.4 – 1.8 | Full vegetative feeding. Maintain consistent watering cycle. |
| Early Flower | 5.8 – 6.2 | 6.0 – 7.0 | 1.4 – 2.0 | Transition to bloom formula (lower N, higher P/K). Watch for deficiencies. |
| Late Flower | 5.8 – 6.2 | 6.0 – 7.0 | 1.4 – 1.8 | Reduce N further. Begin gradual EC taper toward harvest. |
| Flush | 5.8 – 6.0 | 6.0 – 6.5 | 0.0 – 0.4 | Plain water or flushing agent only. Drain salt buildup before harvest. |
CO₂ and light intensity (DLI) are the two most undermonitored variables in home cannabis grows. CO₂ is the raw material for photosynthesis — when CO₂ drops below ambient (400 ppm) because of poor air exchange, your plants slow down regardless of how good everything else is. With supplemental CO₂ (800–1500 ppm) and matching high-intensity lighting, yields can increase 20–40%.
DLI (Daily Light Integral) measures total photosynthetically active radiation over a full day. Cannabis in flower wants 35–65 mol/m²/day. A 600W HPS in a 4×4 tent delivers roughly 30–45 DLI at canopy. Modern 200–400W LEDs can push 40–60 DLI efficiently. GrowAI calculates running DLI from your live lux sensor so you always know the real number — not just your light's marketing claim.
| Growth Stage | CO₂ Target (ppm) | DLI Target (mol/m²/day) | Approx. Lux at Canopy |
|---|---|---|---|
| Seedling / Clone | 400 – 600 | 10 – 20 | 5,000 – 15,000 lux |
| Vegetative | 600 – 1000 | 20 – 40 | 25,000 – 60,000 lux |
| Early Flower | 800 – 1200 | 35 – 55 | 40,000 – 80,000 lux |
| Late Flower | 800 – 1500 | 40 – 65 | 50,000 – 100,000 lux |
| Flush / Pre-Harvest | 400 – 800 | 30 – 50 | 40,000 – 70,000 lux |
Legal Disclaimer: GrowAI is a grow environment monitoring tool for educational and informational purposes. Cannabis cultivation is subject to local, state/provincial, and federal laws. It is your sole responsibility to ensure compliance with all applicable laws in your jurisdiction before growing cannabis. GrowAI does not endorse illegal activity of any kind.