# Coco first grow, week by week

> 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.

- Canonical: https://genetixbay.com/knowledge/guides/coco-first-grow-week-by-week.html
- Category: Start here · Level: Beginner
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Stage: Seedling, Veg, Transition, Flower, Ripening, Harvest · Systems: Coco
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Do I need to feed [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) every time I water?** Yes. Coco coir has almost no nutrients of its own, so feed a complete mineral nutrient at every watering from the first day: about [EC](https://genetixbay.com/knowledge/glossary/ec.md) 0.6–0.8 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) for seedlings, 1.2–1.8 in veg and 1.6–2.2 in flower, at [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.8–6.2. Plain-water waterings in coco starve the plant and swing root-zone EC. Water to 10–20 % [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) so salts don't build up.

**What is the best coco to [perlite](https://genetixbay.com/knowledge/glossary/perlite.md) ratio?** A coco-to-perlite ratio of about 70:30 by volume is the common beginner choice: airy enough to forgive a heavy hand with water, while still holding plenty. Fine, dense coco benefits from more perlite, up to 50:50 for small pots watered often; chunky coco with coarse chips can run at 80:20 or even straight. Mix the perlite into pre-moistened, buffered coco.

**Why do I need to buffer coco?** Raw coco coir holds potassium and sodium on its exchange sites and grabs calcium and magnesium from your feed in exchange, so seedlings can show Ca/Mg deficiency in the first 2–3 weeks. Buffering soaks washed coco in a calcium and magnesium solution (EC about 1.2–2.0 mS/cm, pH 5.8) for 8–24 hours so those sites fill first. Pre-buffered bags can skip it; test runoff anyway.

**How much runoff should I get in coco?** Aim for about 10–20 % runoff per day in coco: for every 1 L you pour in, 100–200 mL should drain out. Runoff carries away excess salts so the root zone stays near your feed EC. If runoff EC rises more than about 0.5–1.0 mS/cm above input, increase the volume or frequency of watering rather than cutting the feed strength.

**How often should I water coco?** Water coco when the pot has lost about 30–50 % of its available water, before it dries out: usually once a day in veg in an 11 L (3 gal) pot, and two to four times a day in flower for big plants in small pots. Coco that dries out completely turns water-repellent and roots suffer. Lift the pot; it should never feel fully light.

**What pH and EC should runoff be in coco?** Coco runoff should usually read pH 5.8–6.5 and an EC within about 0.3–0.5 mS/cm of what you fed in veg, up to about 1.0 above in flower. [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md) climbing week on week means salts are building up: water more volume. Runoff pH falling below 5.5 or rising above 6.8 means adjust your input pH by 0.1–0.2 and check your water.

**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](https://genetixbay.com/knowledge/glossary/photoperiod.md); for autos, sow straight into the final pot and follow the [autoflower guide](https://genetixbay.com/knowledge/guides/autoflower-first-grow-week-by-week.md) for timing. The why is in [coco as a growing system](https://genetixbay.com/knowledge/systems/coco.md).

## What do you need for a coco grow?

A coco grow needs the basic tent kit ([choosing your setup](https://genetixbay.com/knowledge/guides/choosing-your-setup.md)) plus:

- [ ] Washed and buffered [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md), loose or as a compressed block (a 5 kg block makes roughly 60–70 L)
- [ ] Coarse [perlite](https://genetixbay.com/knowledge/glossary/perlite.md), about 30 % of the final volume
- [ ] A calcium/magnesium product or calcium nitrate plus [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md) for buffering (if the coco isn't pre-buffered) ([Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md))
- [ ] A complete mineral nutrient made for coco or hydro, usually a two-part [A+B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md)
- [ ] 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](https://genetixbay.com/knowledge/guides/ph-made-simple.md))
- [ ] EC meter and 1.413 mS/cm calibration solution ([meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md))
- [ ] 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](https://genetixbay.com/knowledge/guides/training-basics.md) |
| 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](https://genetixbay.com/knowledge/glossary/trichome.md) checks |
| 17–20 | Harvest | | Feed to the end; **no [flush](https://genetixbay.com/knowledge/glossary/flushing.md)** | | | | 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](https://genetixbay.com/knowledge/systems/coco.md)). The 10–14 day transition after the flip means "day 1 of flower" lands around week 9–10 here; see the [grow calendar](https://genetixbay.com/knowledge/guides/photoperiod-grow-calendar.md).

## How do you run a coco grow, step by step?

Run a coco grow in these steps:

1. **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].
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](https://genetixbay.com/knowledge/ph-ec/buffering-coco.md)).
3. **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.
4. **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].
5. **Plant.** Sow root-down 0.5–1 cm (¼–½ in) deep ([germinating seeds](https://genetixbay.com/knowledge/guides/germinating-seeds-step-by-step.md)). Water a small ring around the stem.
6. **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](https://genetixbay.com/knowledge/glossary/cal-mag.md), measure EC, then adjust pH last.
7. **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](https://genetixbay.com/knowledge/guides/watering-how-much-how-often.md)).
8. **Empty the saucer** within 30 minutes. Coco sitting in its own runoff wicks salts back up.
9. **Test runoff two or three times a week.** Catch the first 50–100 mL of runoff and read EC and pH ([runoff testing](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)). 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.
10. **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](https://genetixbay.com/knowledge/glossary/high-frequency-fertigation.md)).
11. **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](https://genetixbay.com/knowledge/guides/feeding-basics.md)).
12. **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.
13. **Harvest by trichomes** ([when to harvest](https://genetixbay.com/knowledge/guides/when-to-harvest.md)), then [dry](https://genetixbay.com/knowledge/guides/drying-step-by-step.md) and [cure](https://genetixbay.com/knowledge/guides/curing-step-by-step.md).

## 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](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md).

The valid use is a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) for [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md), 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](https://genetixbay.com/knowledge/diagnosis/rust-spots.md)).
- **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](https://genetixbay.com/knowledge/glossary/wet-dry-cycle.md)** 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](https://genetixbay.com/knowledge/glossary/stock-solution.md) together** or adjusting pH before adding nutrients.
- **Flushing at the end.**

## Evidence

- Coir chemistry: variable, often high [exchange capacity](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) 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](https://genetixbay.com/knowledge/glossary/air-filled-porosity.md) 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*.

## Sources

1. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V, 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241–245. https://doi.org/10.1016/S0960-8524(01)00189-4
2. Greenhouse Grower, 2023. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860
3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. https://doi.org/10.21273/HORTSCI12401-17
4. Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier. https://doi.org/10.1016/C2015-0-01807-5
5. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369
6. Hershkowitz JA, Westmoreland FM, Bugbee B. 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985
7. Saloner A, Bernstein N. 2021. Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.). Industrial Crops and Products 167:113516. https://doi.org/10.1016/j.indcrop.2021.113516
8. Alden MJ, Faust JE. 2025. Exploring the legacy practice of flushing in controlled-environment production of high-CBD cannabis. HortScience 60(10):1818-1825. https://doi.org/10.21273/HORTSCI18752-25