Short answer. In deep water culture (DWC) the roots hang in an aerated nutrient solution, so two things decide success: dissolved oxygen above about 6 mg/L (air running 24/7) and solution at 18–22 °C (64–72 °F). Run pH 5.6–6.0, letting it drift within 5.5–6.2. EC climbs from about 0.6–0.8 mS/cm for seedlings to 1.0–1.6 in veg and 1.4–2.0 in flower. Top off as plants drink and change the solution every 7–14 days. If the air stops, roots can be in trouble within hours.
DWC grows fast and is cheap to build, but it's the least forgiving of the common first-grow systems (choosing a system). The deep detail is in DWC as a system. This guide follows one feminised photoperiod plant in one bucket.
What do you need for a DWC grow?
A DWC grow needs the basic tent kit (choosing your setup) plus:
- [ ] One opaque 19–25 L (5–6.5 gal) bucket per plant, with a light-tight lid that holds a 15–20 cm (6–8 in) net pot
- [ ] Clay pebbles, rinsed until the water runs clear; a rockwool or foam starter plug
- [ ] An air pump sized at roughly 1–2 L/min per 10 L of solution for every bucket plus a margin, with a check valve, airline and an air stone on the bucket floor
- [ ] A spare air pump, and a battery-powered one if your power cuts out
- [ ] A complete hydroponic nutrient (two-part A+B) and a calcium/magnesium supplement if you use RO water
- [ ] pH meter, buffers, pH up and down; EC meter and calibration solution (meter calibration)
- [ ] A waterproof thermometer for the solution; a chiller or a cool room in summer
- [ ] Either a beneficial-microbe root inoculant, or a sterile-reservoir kit you'll commit to (see below)
- [ ] A spare bucket for solution changes, a siphon or small pump, a scrub brush
- [ ] An RCD/GFCI-protected outlet and drip loops on every cable (electrical and water safety)
What do EC, pH and water level look like, week by week?
A DWC grow raises EC gently, keeps pH in a band and lowers the water as roots grow, so roots get both water and air. Weeks count from the seedling breaking the surface of the plug.
| Week | Stage | Light (µmol/m²/s, hours) | EC (mS/cm) | pH band | Water level | Key jobs |
|---|---|---|---|---|---|---|
| 1 | Seedling in plug | 150–250, 18/6 | 0.4–0.6 | 5.8–6.0 | Touching the bottom of the net pot | Hand-water the top of the plug lightly until roots reach the water |
| 2 | Seedling, roots into water | 200–300 | 0.6–0.8 | 5.6–6.0 | Same | Air on 24/7; solution 18–22 °C |
| 3 | Early veg | 300–400 | 0.8–1.0 | 5.6–6.0 | Lower to 2–3 cm (1 in) below the net pot | First full solution change |
| 4–5 | Veg | 400–550 | 1.0–1.4 | 5.6–6.0 | 3–5 cm (1–2 in) air gap | Start LST; roots check weekly |
| 6 | Late veg | 500–600 | 1.2–1.6 | 5.6–6.0 | 3–5 cm gap | Flip at half the final height you can fit; DWC plants grow fast |
| 7–8 | Transition (days 1–14 after the flip) | 600–750, 12/12 | 1.4–1.6 | 5.6–6.0 | Same | Stretch; top off daily; sex check |
| 9–11 | Early flower | 700–900 | 1.4–1.8 | 5.6–6.0 | Same | RH 45–55 %; solution change every 7–10 days |
| 12–14 | Mid flower | 700–900 | 1.6–2.0 | 5.6–6.0 | Same | Plants can drink 2–4 L a day |
| 15–17 | Late flower, ripening | 700–900 | 1.4–1.8, taper only N if you mix salts | 5.6–6.0 | Same | RH 40–50 %; trichome checks |
| 16–19 | Harvest | Feed to the end; no flush | Harvest by trichomes |
DWC plants often veg a week faster than soil, so flip earlier rather than later. The 10–14 day transition still applies: count days since flip and days of flower (grow calendar).
How do you run a DWC grow, step by step?
Run a DWC grow in these steps:
- Set up and test the bucket empty. Fill with plain water, run the air pump for 24 h, and check for leaks, light leaks through the lid and solution temperature. It should stay 18–22 °C (64–72 °F) [1].
- Mix the first solution. Fill with water, add part A, stir, add part B, stir, add Cal-Mag if using RO, then check EC (0.4–0.6 mS/cm for a seedling) and adjust pH to 5.8–6.0 last.
- Plant. Germinate into a rockwool or foam plug (germinating seeds), seat it in the net pot surrounded by clay pebbles, and set the water so it just touches the bottom of the net pot.
- Hand-water the plug with a few millilitres of solution once or twice a day until roots reach the water, usually 5–10 days.
- Run air 24 hours a day. The air pump is life support: warm or still water favours Pythium, which turns roots brown and slimy [2][4]. Extension data from other hydroponic crops show growth inhibition below about 4 mg/L dissolved oxygen and failure below about 3 mg/L [3].
- Lower the water as roots grow. Once a thick mat of roots hangs in the solution, drop the level to leave a 3–5 cm (1–2 in) air gap under the net pot; the roots in that gap get extra oxygen.
- Check every day: solution temperature, the air pump running, water level, pH and EC. Write them down (grow journal).
- Top off between changes. If EC is rising as the level drops, the plant is drinking more than eating: top off with plain pH-adjusted water. If EC is falling, it's eating more: top off with quarter- to half-strength solution [7].
- Let pH drift within the band. A rise of a few tenths a day is normal in a healthy bucket [6] (pH drift). Adjust only when it leaves 5.5–6.2, by small additions.
- Change the solution every 7–14 days. Siphon it out, wipe any film off the walls, inspect the roots, refill at the stage EC and pH, and match the new solution's temperature to the old one.
- Look at the roots weekly. White and fuzzy is healthy; light tan from nutrients is normal; brown, slimy and smelling of swamp is root rot (root browning). Cool the water, raise aeration and act the same day (root rot).
- Feed through to harvest. If you mix single salts, taper only nitrogen over the last 2–3 weeks; otherwise keep the stage feed. Don't flush (below).
- Harvest by trichomes (when to harvest), then dry and cure.
Should the reservoir be sterile or living?
GenetixBay prefers a beneficial-microbe reservoir for DWC. Bacteria will turn up in any reservoir whatever you do, so you may as well have the good ones: add a beneficial root inoculant at each solution change, keep the water cool and aerated, and avoid oxidisers. A sterile reservoir is a valid choice, but only if you commit to it fully: a continuous oxidiser or UV treatment, clean top-up water and no organic additives. It's a personal choice; the half-way house is what fails, for example adding hydrogen peroxide on top of beneficial microbes, which kills the microbes and leaves the roots unprotected. Extension guidance on Pythium in hydroponics stresses temperature, sanitation and oxygen in both approaches [1][5].
Do you flush a DWC plant before harvest?
No. Pre-harvest flushing is a Myth, and in DWC plain water starves the plant almost immediately, in the weeks when it is building most of its final weight and resin. A controlled study found no quality benefit from flushing [8]; see the flush debate. A full solution change replaces old solution in hydro; that's maintenance, not a flush.
How will you know it's working?
You'll know a DWC grow is working when roots are white and the bucket's numbers move slowly and predictably:
- Roots: white or cream, fuzzy with root hairs, growing visibly every few days; no slime, no smell.
- Temperature: solution 18–22 °C (64–72 °F) every day, including the warmest afternoon.
- pH: rises slowly, a few tenths a day, and stays inside 5.5–6.2 with small corrections.
- EC: changes by no more than about 0.2–0.3 mS/cm a day between top-offs.
- Plant: very fast veg, often a node every 1–2 days; leaves held flat and green; no wilting while the water is full.
- Water use: rising steadily week on week; a sudden drop in drinking is an early warning of root trouble.
What mistakes do beginners make in DWC?
DWC beginners mostly lose plants to warm water and stopped air:
- Warm reservoir in summer. Above 24 °C (75 °F) is an alarm, not a target.
- One air pump and no spare. A failure overnight can brown roots by morning.
- Light getting into the bucket: algae, green roots and microbe blooms.
- Chasing pH 5.8 exactly several times a day instead of letting it drift within band.
- Mixing sterile and living methods: peroxide on top of beneficial microbes.
- Leaving the water too high once roots are established, so the root crown never gets air.
- Skipping solution changes and topping off with full-strength feed regardless of EC.
- Water and mains power together without RCD/GFCI protection or drip loops.
- Flushing at the end.
Evidence
- Cool solution and high dissolved oxygen protecting hydroponic roots from Pythium: Established in extension literature for other crops [1][2][3][5]; Pythium and Fusarium confirmed on hydroponic cannabis roots [4].
- pH drift from nitrate uptake and top-off rules by EC: Established hydroponic practice [6][7].
- Cannabis-specific DO and temperature targets and the 1–2 L/min per 10 L air rule: Grower practice.
- Beneficial-microbe reservoir preference: house position; sterile is valid when fully committed.
- Pre-harvest flushing: Myth [8].
