The most common source of error in indoor growing is not missing knowledge about plants — it is an incomplete system concept before the start. Whoever begins and then retrofits, always retrofits under time pressure. Whoever plans beforehand builds correctly once.
This article is not a step-by-step tutorial. It is a planning framework — the order of decisions that makes an indoor grow system viable.
Step 1 — understand the room before planning it
Four parameters determine everything else: temperature without light (baseline), temperature with light (under load), humidity baseline, and available room air for ventilation exchange. These values must be measured — not estimated.
A room at 19 °C in winter and 30 °C in summer has fundamentally different requirements than an air-conditioned basement at constant 21 °C. The ventilation concept, lamp distance and watering frequency depend on it.
| Room parameter | Measurement | Relevant for |
|---|---|---|
| Baseline temperature | Thermometer 24h without light | Ventilation sizing, light power |
| Temperature under load | Thermometer 24h with light | Exhaust requirement, VPD target reachability |
| Baseline humidity | Hygrometer 24h | Humidifier/dehumidifier requirement |
| Room volume (m³) | L × W × H | Ventilation sizing (air changes/h) |
| Power outlets | Count + check fuse capacity | Total load planning |
Step 2 — light: intensity before technology
The decision for a lamp does not begin with the technology (LED, HPS, CMH) but with the target PPFD on the cultivation area. For a 40 × 40 cm area (0.16 m²) a target PPFD of 800 µmol/m²/s means: 800 × 0.16 = 128 µmol/s total photon flux. With a lamp at 2.5 µmol/J efficiency: 128 / 2.5 = approximately 51 watts actual power consumption.
This explains why an efficient 50–80W LED setup is sufficient for a compact format — and why 300W "for beginners" in a 40 × 40 cm tent is a waste of money with overheating risk.
Step 3 — ventilation: negative pressure as basic principle
A correctly sized ventilation system creates slight negative pressure in the grow room: exhaust slightly exceeds intake. The result: air flows through defined paths, not through leaks. Odours do not escape. This is not a comfort feature — it is the prerequisite for controlled climate conditions.
The exhaust dimensioning depends on the room volume. Rule of thumb: the entire room volume should be exchanged 60× per hour. For a 140 × 40 × 40 cm system (0.224 m³): 0.224 × 60 = approximately 14 m³/h minimum exhaust. In practice, significantly more is installed (factor 2–3) to absorb filter resistance, heat load and peak load.
| Grow box format | Volume (m³) | Minimum exhaust | Recommended exhaust |
|---|---|---|---|
| 40 × 40 × 140 cm | 0.22 | 14 m³/h | 30–50 m³/h |
| 60 × 60 × 140 cm | 0.50 | 30 m³/h | 60–100 m³/h |
| 80 × 80 × 160 cm | 1.02 | 61 m³/h | 120–200 m³/h |
| 120 × 60 × 180 cm | 1.30 | 78 m³/h | 150–250 m³/h |
Step 4 — watering: manual or automatic?
Manual watering is the most common choice for beginners — no investment, immediately usable. The disadvantage: watering quality depends on consistency and attention. Holiday breaks are problematic. Night watering is impractical.
Automation makes economic sense for serious grow interest: a load cell system costs 30–60 euros in components and consistently delivers better results than manual watering by feel. The Growix OS controls the pump logic based on weight loss — the plant itself signals when it needs water.
Step 5 — sensors: what must be measured
Minimum equipment for a controlled grow:
- Temperature + humidity at canopy level — for VPD calculation and climate control
- pH meter — before each watering
- EC meter — when fertilising
Extended equipment for full control:
- Substrate weight (load cell) — watering control
- Infrared thermometer — leaf surface temperature for precise leaf VPD
- PAR meter (quantum sensor) — PPFD measurement at canopy height
Step 6 — plan light cycle and phase changes
The light cycle is the control of the entire grow. For photoperiod strains:
| Phase | Light cycle | Typical duration |
|---|---|---|
| Germination | 18–20h light | 3–7 days |
| Vegetative | 18h light / 6h dark | 3–8 weeks |
| Flower (flip) | 12h light / 12h dark | 7–12 weeks strain-dependent |
| Late flower / flush | 12h / 12h (unchanged) | 1–2 weeks |
The moment of the flip (switch to 12/12) is the most critical planning variable: most strains "stretch" by another 50–150% of their current height afterward. Whoever has 50 cm at the flip can stand at 75–125 cm at the end of the stretch phase — that must align with the room height concept.
The Growix Core concept
The Growix Core solves all six steps as a system: 140 × 40 × 40 cm room format with defined PPFD profile, integrated 3-channel ventilation system with negative pressure principle, load cell watering automation, SHT4x climate sensors at canopy level, and a Raspberry Pi OS that logs and controls all parameters. No retrofitting of components, no compromise at the start.