# Buffering coco coir: why it matters and how to do it

> Coco coir has a high cation exchange capacity that arrives loaded with potassium and sodium. Unbuffered, it grabs calcium and magnesium from your feed and releases K and Na, causing early Ca/Mg deficiency. Buffering means soaking washed coco in a calcium (and usually magnesium) nitrate solution so the exchange sites are filled with Ca and Mg before planting, then rinsing. It is standard grower and industry practice with sound chemistry behind it, though controlled studies on cannabis are lacking.

- Canonical: https://genetixbay.com/knowledge/ph-ec/buffering-coco.html
- Category: pH and EC · Level: Intermediate
- Evidence: Grower practice · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Seedling, Veg · 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 buffer [coco coir](https://genetixbay.com/knowledge/glossary/coco-coir.md)?** Yes, you should buffer coco coir unless a runoff test confirms a 'pre-buffered' bag is ready. Coco has a high cation exchange capacity, about 32–130 cmol/kg, that arrives loaded with potassium and sodium, and unbuffered coco pulls calcium and magnesium from your feed for the first few weeks. The chemistry is established; the cannabis benefit is grower practice without controlled trials.

**How do I buffer coco with [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) or [calcium nitrate](https://genetixbay.com/knowledge/glossary/calcium-nitrate.md)?** To buffer coco, start with washed coco, then soak it in calcium nitrate plus a magnesium salt, or a strong Cal-Mag product, at roughly 150–300 mg/L calcium and 50–100 mg/L magnesium, [EC](https://genetixbay.com/knowledge/glossary/ec.md) about 1.2–2.0 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), adjusted to [pH](https://genetixbay.com/knowledge/glossary/ph.md) 5.8–6.0. Soak 8–24 hours, drain, rinse with low-EC water, and test runoff for EC below about 0.6–1.0 mS/cm. These strengths are grower practice.

**Why does my plant get calcium deficiency in new coco?** Cannabis plants often show calcium deficiency in new coco because unbuffered coir's exchange sites grab calcium and magnesium from the feed and release potassium and sodium in exchange. The extra potassium then competes further with calcium and magnesium uptake. Buffering beforehand, and feeding slightly more calcium and magnesium for the first 2–3 weeks, prevents it.

**What is the difference between washed and buffered coco?** Washed coco has been rinsed with fresh water to remove soluble salts and lower its EC, but washing cannot fully clear the potassium and sodium held on the coir's exchange sites. Buffered coco has also been soaked in a calcium and usually magnesium solution, so divalent calcium displaces those monovalent ions, which are then rinsed away. Buffering needs washed coco first.

**How long should I soak coco to buffer it?** Coco coir is usually soaked for 8–24 hours to buffer it, mixed once or twice so it saturates evenly; one retailer protocol uses about 45 g of calcium nitrate in 7 L of water for a 600 g block over 12 hours. Very high-potassium or high-sodium coco may need a second soak. Confirm the result by testing runoff EC and pH afterwards.

**Can I reuse coco without buffering?** Yes, reused coco usually does not need full re-buffering, because its exchange sites are already loaded with your previous feed's calcium and magnesium. Rinse it well, check that runoff EC has come down, and remove old roots before replanting. This is grower practice rather than a tested protocol, so a runoff check is the best guide.

**Short answer.** Coco coir has a high cation exchange capacity (CEC) that comes loaded with potassium and sodium from the coconut and from salt water used in processing [1][2]. Unbuffered, it pulls calcium and magnesium out of your feed and releases K and Na, so young plants show Ca/[Mg deficiency](https://genetixbay.com/knowledge/glossary/magnesium.md) in the first weeks. **Buffering** means soaking washed coco in a calcium (usually plus magnesium) nitrate solution so the exchange sites fill with Ca and Mg before planting, then rinsing [3]. The chemistry is sound; cannabis-specific trials are lacking, so the method is *grower practice*.

## What's happening

Coir particles carry negative charges that hold cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and swap them with the solution. Reported coir properties vary widely by source: CEC about 32–130 cmol/kg, pH 4.9–6.9, total K about 0.4–2.4% of [dry weight](https://genetixbay.com/knowledge/glossary/dry-weight.md), with large source-to-source differences in Na and Cl [2]. Abad et al. found commercial coir dusts suitable as peat substitutes but chemically variable, with high K and Na in some lots [1].

- **Washing** (with fresh water) removes soluble salts, lowering EC, but cannot fully clear ions held on exchange sites [3].
- **Buffering** uses mass action: flood the coco with Ca²⁺ (and Mg²⁺). Divalent Ca is held more strongly than K⁺ and Na⁺; each Ca²⁺ adsorbed displaces two monovalent ions, which you then rinse away [3].

If you skip it, the coco buffers itself using *your feed*, for the first few weeks: Ca and Mg disappear onto the coco, K and Na come out, and high K competes further with Ca and Mg uptake [4][5].

## Numbers that matter

| Parameter | Value | Notes |
|---|---|---|
| Coir CEC | ~32–130 cmol(+)/kg dry | [2]; varies by source and age |
| Coir pH | ~4.9–6.9 | [2] |
| Coir total K | ~0.4–2.4% dry weight | [2] |
| Rough Ca needed to load 1 kg dry coco | ~10–25 g Ca (≈50–130 g calcium nitrate) | Back-of-envelope from CEC 50–130 cmol/kg assuming full exchange; real exchange is partial. |
| Example supplier protocol | ~45 g calcium nitrate in 7 L for a 600 g block, 12 h | One retailer guide [6]; equals ~75 g per kg dry coco |
| Buffering solution, home practice | Ca 150–300 mg/L + Mg 50–100 mg/L, EC ~1.2–2.0 mS/cm | *Grower practice*; often a Cal-Mag product at strong rate. |
| Target runoff after buffering | EC <0.6–1.0 mS/cm, pH 5.8–6.5 | *Grower practice* |

## How to buffer coco

1. **Start with washed coco.** If the bag says "unwashed", rinse with fresh water until runoff EC is below about 0.5 mS/cm.
2. **Mix the buffer solution**: calcium nitrate (plus [magnesium sulfate](https://genetixbay.com/knowledge/glossary/magnesium-sulfate.md) or [magnesium nitrate](https://genetixbay.com/knowledge/glossary/magnesium-nitrate.md)) in water, or a Cal-Mag product, to the strength above. Adjust to pH 5.8–6.0.
3. **Soak** the coco fully for 8–24 hours, mixing once or twice so it saturates evenly.
4. **Drain**, then **rinse** with plain or low-EC water to remove the released K and Na.
5. **Test runoff** EC and pH. Optional but useful: one lab test of runoff for K, Na and Ca on a new coco supplier.
6. **Optional second soak** for very high-K/Na coco.
7. **Plant, and feed with a full nutrient solution from day one,** slightly higher in Ca and Mg for the first 2–3 weeks.

Reused coco: it has been loaded with your feed's cations already; rinse well, check runoff EC, and remove old roots. It usually does not need full re-buffering. *Grower practice.*

## Common mistakes

- Treating "pre-buffered" bags as guaranteed. Test runoff anyway.
- Buffering with plain water and calling it done.
- Planting into buffered coco and then giving plain water for a week; the [seedlings](https://genetixbay.com/knowledge/glossary/seedling.md) still need Ca and Mg.
- Using salty [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) to rinse, undoing the job (see [sodium](https://genetixbay.com/knowledge/nutrients/sodium.md)).

## Evidence

- Coir has a variable, often high CEC and variable K, Na and Cl: *Established* [1][2].
- Calcium-loading displaces K and Na from exchange sites: *Established* chemistry [5]; practical protocols are *grower and industry practice* [3].
- Buffering improves cannabis outcomes: *Grower practice*; no controlled cannabis study found.

## 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. Minnesota Pollution Control Agency. Chemical and physical properties of coir. https://stormwater.pca.state.mn.us/Chemical_and_physical_properties_of_coir
3. Greenhouse Grower. Washed, low-EC, or buffered? How to specify coco substrate for your crop. https://www.greenhousegrower.com/?p=180860
4. Saloner A, Sacks MM, Bernstein N. 2019. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369
5. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9
6. Living Seeds. Washed coco coir block: buffering instructions (retailer guide). https://www.livingseeds.co.za/600g-cocopeat-block