"Set the timer to 4 times a day — the system waters itself." But a drip system on autopilot is a timer that has no idea whether the substrate dried out between irrigations, whether water was still sitting in the pot from the last cycle, or whether drainage EC has crept up to 4.5 from salt accumulation. The irrigation schedule in a drip system depends on crop, substrate, lighting, temperature, and growth stage — and "4 times a day" may be correct on Monday and catastrophically too little or too much on Friday when light intensity or temperature has shifted.
Quick Glossary
- Dripper — a device that delivers solution in drops or a small flow; available as pressure-compensated (constant output regardless of pressure) or non-compensated (pressure-dependent)
- Irrigation schedule — the frequency and volume of each irrigation event; determines substrate moisture level and salt accumulation between irrigations
- Drainage EC — the electrical conductivity of solution exiting the substrate; the key indicator of whether the irrigation schedule is correctly set
Dripper Types and Where Each One Fits
Pressure-compensated drippers — stable output (e.g. 2 L/hr) regardless of system pressure within the 0.5–4 bar range. Every plant receives the same volume regardless of distance from the pump or substrate height. Mandatory for systems with more than 10–15 plants or on uneven surfaces where pressure difference between near and far drippers is significant.
Non-compensated drippers — output depends on pressure. Plants closest to the pump receive more solution; those furthest away receive less. Acceptable for small systems (3–5 pots) with level placement. In uneven systems, plants at the end of lines are chronically under- or over-irrigated.
Dripper vs. stake — the stake form factor for pots and containers allows solution to be directed precisely to the root zone. Without a stake, the dripper delivers solution to the substrate surface and achieves even wetting only with the right substrate — works well with coco and peat, but on coarse LECA the solution may run down the sides.
Irrigation Schedule: How to Calculate Instead of Guess
The correct irrigation schedule is defined by one criterion: the substrate should remain "moist but not wet" between irrigations — and each irrigation event should produce 10–20% drainage relative to the volume delivered.
"10–20% drainage" is the critical number. Below 10% drainage, salts accumulate in the substrate between irrigations and root zone EC rises. Above 30–40% drainage, too much solution runs out unused, fertiliser consumption is high, and there is a risk of waterlogging in the lower substrate layer.
How to set it up: run one irrigation cycle and measure the drainage volume. No drainage — increase volume or frequency. Drainage above 30% — reduce irrigation volume. Once dialled in, measure drainage EC and compare it to input solution EC.
Irrigation frequency depends on DLI — at higher DLI the plant transpires more and the substrate dries faster. A practical rule: at 200 µmol/m²/s LED and 16 hr/day with coco in a 10-litre pot — 4–6 irrigations per day at 200–300 mL each. At higher light levels or smaller pots, irrigate more frequently.
Salt Accumulation and Drainage EC
Drip irrigation is the most common setup where salt accumulation goes unnoticed. The mechanism: between irrigations the plant absorbs water more actively than nutrients, and the solution remaining in the substrate concentrates. With insufficient drainage (<10%), the concentrated residue from the previous irrigation mixes with the new one and EC gradually climbs.
How to track it: measure drainage EC once a week. If drainage EC exceeds input EC by 1.5 or more:
- Increase single-irrigation volume to produce 20–25% drainage, or
- Perform a flush — run 2–3 substrate volumes of plain water or a weak solution (EC 0.4–0.6) until drainage EC equalises
Three Mistakes That Cost the Most
Setting the timer once and never revisiting it when conditions change. The irrigation schedule for tomatoes in September at 14 hours of light and 22°C is not the same as in July at 18 hours and 28°C. Transpiration and water consumption change significantly. Review irrigation frequency when the season changes, growth stage shifts, or light intensity is adjusted.
Not checking output uniformity across drippers. Accumulated slime, calcium deposits, or physical damage to a dripper — and one plant receives 50 mL instead of 200 mL. Check each dripper's output every 2–4 weeks by collecting its flow in a measuring cup.
Ignoring drainage EC in a drip system. A drip system where drainage EC is never measured is a system where salt accumulation is only discovered once osmotic stress symptoms appear. Early drainage EC monitoring prevents the problem rather than reacting to it.
How to Know the Drip System Is Set Up Correctly
- Each dripper delivers the same volume when checked
- Drainage after irrigation is 15–20% of the delivered volume
- Drainage EC is consistently 0.3–0.5 above input EC and is not rising week to week
- Substrate between irrigations feels "springy and moist" when squeezed — not wet and not dry
- Plants are uniform in size and development — a sign of even solution delivery