Drip Frequency for Rockwool: Minutes Per Cycle

Drip frequency for rockwool is minutes per cycle set from a dryback target against an 80% field capacity: rockwool holds more water than coco (75%) or soil (45%), so the shot and the gap between events change with the medium, not the calendar. The timer formula divides substrate volume x dryback by delivery rate, scales by stage, VPD and root-zone temperature, then reads runoff, moisture and EC drift off the safety bands of dryback 10-30%, runoff 15-25% and moisture 50-75%.

How Irrigation Timer Calculator — Drip, Schedule & Dryback Blueprint Helps You Master This

1. Pick the medium and the stage: field capacity by substrate — coco 75%, rockwool 80%, soil 45%, perlite 35%, clay 50% — decides the water bank the dryback rolls against.
2. Set the dryback target: the percent of that bank you want transpired between events, 10–30% for the working band, higher with higher EC for generative steering.
3. Compute irrigation time: substrate litres × dryback ÷ (flow L/h ÷ 60 × emitters), scaled by stage (seedling 0.5, veg 0.8, flower 1.0, fruit 1.2), VPD factor and root heat (+2% per °C over 20).
4. Adjust events per day: base frequency × VPD × (1 + 0.05(T − 20)) — a dry hot room waters more often without a manual change.
5. Close the loop on runoff and moisture: runoff = (shot − substrate × (1 − dryback) × FC) ÷ shot; moisture = 100 − dryback actual — no drainage means every fed ion stays in the pot.
6. Read the safety band: dryback 10–30 %, runoff 15–25 %, moisture 50–75 % green; the red edges are dryback <5 or >45, runoff <10 or >35, moisture <40 or >85 — and the EC drift line tells you what no-runoff is really costing.

The Formula Behind the Result

• Irrigation timer minutes — the dryback shot divided by drip delivery → T = frac{V_s cdot d}{frac{q}{60} cdot n} cdot f_{stage} cdot f_{vpd} cdot f_{temp}
• Events per day — base frequency adjusted by VPD and root heat → f_d = f_b cdot f_{vpd} cdot left(1 + 0.05,(T_r - 20)right)
• Runoff — the drainage your shot actually produces → R = frac{V_{shot} - V_s(1 - d),FC}{V_{shot}} cdot 100
• Actual dryback — target corrected for how thirsty the air is → d_{act} = d cdot left(1 + (1 - f_{vpd}) cdot 0.2right)
• Water per day — shots summed across the day → V_{day} = frac{T}{60} cdot q cdot n cdot f_d
• Substrate moisture — what the sensor should read after dryback → M = 100 - d_{act}
• EC drift — the salt your runoff leaves behind → Delta EC = EC_{t} cdot left(1 - frac{R}{100}right) cdot 0.1
• Safety bands — dryback, runoff and moisture → d,10{-}30, R,15{-}25, M,50{-}75 text{ GREEN} text{vs} text{RED: } d<5 ,|, d>45 ,|, R<10 ,|, R>35 ,|, M<40 ,|, M>85

Target Ranges: What the Numbers Should Be

• Field capacity by substrate is the locked baseline: coco 75%, rockwool 80%, soil 45%, perlite 35%, clay 50% — the archived engine held a comparable per-medium water-holding table and sized shot volume off it.
• Irrigation time on the defaults — 10 L of coco, 20% dryback, ten 2 L/h emitters, flower stage — lands 6.0 minutes; flip the stage to seedling (0.5) and it halves to 3.0 minutes exactly, which is why the seedling line reads short.
• Honest runoff: a 6-minute shot pours 2.0 L into 10 L of dry coco that can hold back 6.0 L — the event never drains, so runoff real is 0% and the safety band trips red on the runoff edge. Hitting 15–25% drainage needs a shot near the storage (roughly 7–8 L), a proper water-on-water event, not a dry pulse.
• Dryback and moisture move together by construction: actual dryback = target × (1 + (1 − VPD) × 0.2); moisture = 100 − dryback actual. At the 20% target moisture reads 80%, a touch past the 75% top of the green band.
• EC drift is the honest consequence of zero runoff: ΔEC = EC target × (1 − runoff ÷ 100) × 0.1, so with no drainage at a 1.8 mS feed, salts accumulate ~0.18 mS/day — the runoften 15–25% keeps drift near zero and this panel shows exactly why you flush.

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Related guides

Rockwool slab: dryback to drip minutes

Slab: 10 L of rockwool at 80% field capacity, two 2 L/h emitters (4 L/h total), flower stage, 20% dryback target, VPD factor 1.0, root-zone at 22 C. Field capacity fixes the water bank; the dryback fixes how much of it the plant removes between events.

Frequently Asked Questions

References & Science

• USDA National Agricultural Library
• HortScience — hydroponic nutrient studies
• Cornell CALS — hydroponic research manual

Frequently asked questions

References

• ASTM D1125 — Standard Test Methods for Electrical Conductivity and Resistivity of Water
• APHA Standard Methods 4500-H — pH value (electrometric)
• Resh, H. M. — Hydroponic Food Production (7th ed.), CRC Press

Related resources

• All Water chemistry tools
• More Growing systems guides
• Open Water Quality Analyzer
• Open Ph Alkalinity Architect