Ebb and Flow Flood Cycle Timer Calculator
Calculate optimal flood and drain cycle timing for ebb and flow hydroponic systems by media and plant stage.
Ebb and flow (flood and drain) systems work by periodically flooding the grow tray with nutrient solution, then draining it back to the reservoir. Timing the flood cycles correctly ensures roots get nutrients and oxygen in the right balance.
Key Variables:
- Grow media type: different media retain water differently
- Plant growth stage: seedlings need less frequent flooding than fruiting plants
- Temperature and humidity: hot, dry conditions require more frequent cycles
- Light period: most flooding happens during lights-on; reduce or stop during lights-off
Media Water Retention:
| Media | Retention | Drain Time | Flood Frequency |
|---|---|---|---|
| Expanded clay (LECA) | Low | Fast (2–3 min) | Every 2–3 hours |
| Perlite | Low-medium | Fast (2–3 min) | Every 2–4 hours |
| Rockwool cubes | High | Slow (5–8 min) | Every 4–6 hours |
| Coconut coir | High | Medium (3–5 min) | Every 4–6 hours |
| Growstones | Medium | Fast (2–3 min) | Every 3–4 hours |
Growth Stage Multiplier:
- Seedling/Clone: ×0.5 (half frequency — roots are delicate)
- Vegetative: ×1.0 (standard frequency)
- Flowering/Fruiting: ×1.2 (slightly more frequent — higher demand)
Temperature Adjustment:
- Below 70°F (21°C): reduce frequency by 25%
- 70–80°F (21–27°C): standard frequency
- Above 80°F (27°C): increase frequency by 25%
Flood Duration: The tray should fill to 1–2 inches below the top of the media. Standard flood time is 10–15 minutes — enough for the solution to wick to the top, then drain completely.
Worked Example — LECA media, vegetative stage, 78°F:
- Base interval (LECA): 2.5 hours
- Stage multiplier (veg): ×1.0
- Temp adjustment: standard
- Flood every 2.5 hours during lights-on
- Flood duration: 15 minutes
- For 18-hour light period: 18 / 2.5 = 7 floods per day
- One optional flood 2 hours into dark period
Lights-Off Rule: During the dark period, reduce to 0–1 flood cycles. Roots need oxygen, and over-watering during dark hours promotes root rot.