Short answer. Coco is hydroponics that looks like soil. Use buffered coco mixed about 70:30 with perlite, feed a complete mineral nutrient at every watering from day one at pH 5.8–6.2, and water to 10–20 % runoff before the pot dries out. Feed EC climbs from about 0.6–0.8 mS/cm for seedlings to 1.2–1.8 in veg and 1.6–2.2 in flower, fed right to harvest. Never let coco dry out completely.
Coco grows faster than soil because roots get more air, but it forgives less: there's no starter charge and little buffer. This guide follows one feminised photoperiod plant; for autos, sow straight into the final pot and follow the autoflower guide for timing. The why is in coco as a growing system.
What do you need for a coco grow?
A coco grow needs the basic tent kit (choosing your setup) plus:
- [ ] Washed and buffered coco coir, loose or as a compressed block (a 5 kg block makes roughly 60–70 L)
- [ ] Coarse perlite, about 30 % of the final volume
- [ ] A calcium/magnesium product or calcium nitrate plus magnesium sulfate for buffering (if the coco isn't pre-buffered) (Cal-Mag)
- [ ] A complete mineral nutrient made for coco or hydro, usually a two-part A+B
- [ ] 7–19 L (2–5 gal) pots with good drainage, raised on a tray or saucer you can empty
- [ ] pH meter, buffers, pH up and down (pH made simple)
- [ ] EC meter and 1.413 mS/cm calibration solution (meter calibration)
- [ ] A 10–20 L (3–5 gal) mixing bucket with a lid, measuring syringes and a stirring stick
- [ ] A measuring jug and a small cup to catch runoff for testing
- [ ] Optional: a pump-and-dripper kit and a timer for automatic watering later
How much runoff and EC does coco need, week by week?
Coco needs feed at every watering, with EC rising steadily and runoff checked a few times a week. Weeks count from the seedling breaking the surface; EC is the total of your water plus nutrients, in mS/cm (ppm500 = EC x 500).
| Week | Stage | Light (µmol/m²/s, hours) | Feed EC | pH | Waterings | Runoff target | Key jobs |
|---|---|---|---|---|---|---|---|
| 1 | Seedling | 150–250, 18/6 | 0.6–0.8 | 5.8–6.0 | Small ring, 50–150 mL, every 1–2 days | Little or none | Keep coco moist, never soaking |
| 2 | Seedling | 200–300 | 0.8–1.0 | 5.8–6.0 | 150–300 mL daily | A few drips | Watch for rust spots (Ca/Mg) |
| 3 | Early veg | 300–400 | 1.0–1.2 | 5.8–6.2 | 0.3–0.6 L daily | 10–20 % | Pot up from a cup if used |
| 4–5 | Veg | 400–550 | 1.2–1.5 | 5.8–6.2 | 0.5–1.5 L, once a day | 10–20 % | Start LST |
| 6–7 | Late veg | 500–600 | 1.4–1.8 | 5.8–6.2 | 1–2 L, 1–2 times a day | 10–20 % | Flip at half the final height you can fit |
| 8–9 | Transition (days 1–14 after the flip) | 600–750, 12/12 | 1.6–1.8 | 5.8–6.2 | 1.5–3 L, 1–3 times a day | 10–20 % | Stretch; tie down; sex check |
| 10–12 | Early flower | 700–900 | 1.6–2.0 | 5.8–6.2 | 2–4 L split over 2–3 waterings | 10–20 % | RH 45–55 %; tuck, don't pluck |
| 13–15 | Mid flower | 700–900 | 1.8–2.2 | 5.8–6.2 | 2–5 L split over 2–4 waterings | 15–20 % | Runoff EC check twice a week |
| 16–18 | Late flower, ripening | 700–900 | 1.6–2.0; taper only N if you mix salts | 5.8–6.2 | Same | 15–20 % | RH 40–50 %; trichome checks |
| 17–20 | Harvest | Feed to the end; no flush | Harvest by trichomes |
These are Grower practice steps that sit inside the published coco range of about EC 1.2–2.4 mS/cm with 10–20 % runoff (coco). The 10–14 day transition after the flip means "day 1 of flower" lands around week 9–10 here; see the grow calendar.
How do you run a coco grow, step by step?
Run a coco grow in these steps:
- Hydrate and rinse. Break up the block in a tub with warm water. Rinse with fresh water until runoff EC is below about 0.5 mS/cm, unless the bag says washed and a runoff test agrees [2].
- Buffer, unless pre-buffered. Soak the coco 8–24 hours in a calcium and magnesium solution at EC about 1.2–2.0 mS/cm and pH 5.8, mixing once or twice, then drain and rinse. Without this, raw coco pulls Ca and Mg out of your feed and releases potassium and sodium for the first few weeks [1][5] (buffering coco).
- Mix in perlite. About 70 % coco to 30 % coarse perlite by volume. Use more perlite (up to 50:50) for fine, dusty coco or small pots watered often; less for chunky coco.
- Fill and pre-wet with feed, not plain water: seedling-strength solution at EC 0.6–0.8 and pH 5.8–6.0 until it drips. Coco has no starter charge, so the seedling needs nutrients from day one [3].
- Plant. Sow root-down 0.5–1 cm (¼–½ in) deep (germinating seeds). Water a small ring around the stem.
- Mix every feed the same way. Fill the bucket with water, add part A, stir, then part B, stir (never mix concentrates together), add any Cal-Mag, measure EC, then adjust pH last.
- Water to runoff before it dries. When the pot has lost about 30–50 % of its water (it feels noticeably lighter, the top 1–2 cm is dry), water slowly until 10–20 % drains out. Never let coco dry right out: it turns water-repellent (watering).
- Empty the saucer within 30 minutes. Coco sitting in its own runoff wicks salts back up.
- Test runoff two or three times a week. Catch the first 50–100 mL of runoff and read EC and pH (runoff testing). If runoff EC is more than 0.5–1.0 mS/cm above input, water more volume or more often rather than lowering the feed.
- Water more often as roots fill the pot. By mid flower, a big plant in an 11 L (3 gal) pot may need two to four smaller waterings a day. That is normal coco behaviour and part of why coco can grow big plants in small pots (high-frequency fertigation).
- Raise EC by stage, not by guesswork. Step up about 0.2 mS/cm at a time when leaves are deep green with no burnt tips. Higher nutrient strength didn't raise yield or cannabinoids in a controlled trial [6] (feeding basics).
- Flip, then feed through to harvest. If you mix single salts, taper only nitrogen over the last 2–3 weeks while keeping the rest fed [7]. Do not flush.
- Harvest by trichomes (when to harvest), then dry and cure.
Should you flush coco before harvest?
No. Pre-harvest flushing is a Myth, and in coco it is especially harsh: with no nutrient reserve in the medium, plain water starves the plant within days, in the weeks when it is packing on most of its final weight and resin. A controlled study found no quality gain from flushing [8]; see the flush debate.
The valid use is a root-zone flush for salt build-up, at any stage: water 2–3 pot volumes of a light feed (EC about 0.4–0.8 mS/cm with Ca and Mg, pH 5.8–6.0), not plain water, then return to the normal feed.
How will you know it's working?
You'll know a coco grow is working when plants grow fast and evenly and the runoff numbers stay close to the input:
- Weeks 1–3: no rust spots or pale interveinal patches on new-ish leaves (the classic sign of unbuffered coco pulling Ca and Mg) (rust spots).
- Veg: a new node every 2–3 days, faster than soil, with mid to deep green leaves held flat.
- Pots: go from heavy to noticeably lighter within a day in veg; never bone dry.
- Runoff: pH 5.8–6.5, EC within 0.3–0.5 mS/cm of input in veg and within about 1.0 in flower, stable week on week.
- Flower: steady bud swell; oldest fan leaves fade slowly only in the last 2–3 weeks.
What mistakes do beginners make with coco?
Coco beginners usually treat it like soil:
- Plain-water waterings. Every watering carries feed in coco.
- Unbuffered coco and early Ca/Mg deficiency in weeks 1–3.
- Letting it dry out between waterings. Coco forgives overwatering better than soil but punishes drying.
- No runoff. Salts build up and the plant shows burnt tips and clawing while runoff EC climbs.
- Fixing high runoff EC by cutting feed strength instead of watering more volume.
- Too little perlite in fine coco: soggy pots, slow growth, fungus gnats.
- Mixing nutrient concentrates together or adjusting pH before adding nutrients.
- Flushing at the end.
Evidence
- Coir chemistry: variable, often high exchange capacity loaded with K and Na: Established [1]. Buffering protocols: Grower and industry practice [2].
- Ca and K interactions in cannabis nutrition: Supported [5].
- Feeding from early on in coir-based media: Supported [3]. Higher nutrient strength not increasing yield: Supported [6].
- Air-filled porosity and perlite in container media: Established [4].
- Nitrogen trade-off: Supported [7]. Pre-harvest flushing: Myth [8].
- Weekly EC, volumes and the 70:30 ratio: Grower practice.
Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.Perlite is a light, white, puffed volcanic glass added to growing mixes to increase drainage and air space; it is chemically inert and holds no nutrients.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm.The daily length of light versus dark; photoperiod cannabis flowers when nights grow long enough, rather than at a fixed age.Magnesium sulfate heptahydrate, sold as Epsom salt, is the common hydro magnesium source, supplying about 9.9% magnesium and 13% sulfur.Runoff EC is the conductivity of solution draining from the pot; compared with input EC, it shows whether salts are building up or being used up in the root zone.A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.Feeding only plain water for days or weeks before harvest to "clean" the plant; GenetixBay rates it a Myth that harms yield, unlike a root-zone salt flush.Cal-Mag is a supplement supplying calcium and magnesium, usually as nitrates; need depends on cultivar, water source (RO vs tap) and medium (coco), not on LED lighting.The wet-dry cycle is the alternation between watering a container and letting it dry back, which refreshes oxygen in the root zone between irrigations.A stock solution is a concentrated nutrient mix, often 100x or 200x final strength, diluted into the reservoir; calcium and sulfate/phosphate stocks must stay separate.Cation exchange capacity (CEC) is a medium's ability to hold positively charged nutrients such as calcium, magnesium and potassium on its surfaces and release them later.Air-filled porosity is the share of a container's volume that holds air rather than water after it has drained, a key factor in root oxygen and overwatering risk.
