💧 Dry Back Calculator
Calculate target substrate VWC% at dry back based on peak field capacity and desired dry back percentage.
Inputs
%
%
Dry Back VWC% Goal
60% × (1 − 0.40) = 60% × 0.60
36%
Dry Back Range Context
Your dry back:
40% — Moderate
Wetter (veg)
Drier (gen)
🔥 Generative
30–50%
Dry back
🌿 Vegetative
10–25%
Dry back
At 40% dry back, you're in generative territory — steering the plant toward fruiting and reproductive growth.
Dry Back Curve Visualization
📖 What is Dry Back?
Dry back is the intentional reduction of substrate VWC% (volumetric water content) between irrigation events. After reaching peak VWC at field capacity, the crop is allowed to transpire and deplete moisture to a target level before the next irrigation cycle.
Managing dry back gives you direct control over plant stress response, root development, and generative vs vegetative growth balance.
⚖️ Generative vs Vegetative
- Generative Higher dry back (30–50%+) — triggers stress response, promotes flowering, fruiting, and root zone development. Less water = reproductive signal.
- Vegetative Lower dry back (10–25%) — keeps substrate wetter, promotes shoot growth, canopy expansion, and vigorous vegetative development.
- Transition timing and magnitude determine how aggressively you steer the crop.
📐 How to Use This Calculator
- Set Target Peak VWC% to the water content at the top of your irrigation cycle (field capacity for your substrate).
- Set Dry Back % to how much you want to reduce from peak.
- The Dry Back VWC% Goal is the substrate reading where you trigger the next irrigation.
- Monitor your substrate sensors and irrigate when VWC hits the goal.
🔗 Resources
- Athena crop steering protocols vary by cultivar, growth stage, and environment. Calibrate with your local data.
- Dry back targets interact with EC strategy — a heavier dry back often pairs with lower frequency, higher EC shots.
- Sensor placement matters: measure at mid-slab, not edges.