Spike's Grow School
How to Buffer Coco Coir
Plant into fresh coco without buffering and the first few weeks can go sideways: yellowing leaves and a calcium-magnesium deficiency that seems to come from nowhere. It isn't your feed, it's the coir quietly stripping cal-mag before your plants get a look in. Buffering fixes that before you ever plant.
This is the hands-on companion to our coco coir guide, one piece of our wider guide to hydroponic growing media. We'll keep the science short (it lives in the coco coir guide, linked, if you want the full story) and spend our time on the doing: the two methods that actually work, the numbers worth trusting, and how to know when it's done. Prickly business, buffering. Let's make it simple.
First, what buffering actually does
Coco's fibres hold a mild negative charge, so they cling to positively charged nutrients. Fresh coir comes with those sites loaded up with sodium and potassium. The problem is that coco much prefers calcium and magnesium (they carry a double positive charge), so the moment you feed, the coir grabs the calcium and magnesium out of your solution and lets its sodium and potassium go in exchange. Your plants go hungry for calcium and magnesium even though you're feeding them.
Buffering fixes this by soaking the coir in a calcium-rich (usually calcium-and-magnesium) solution first, so those exchange sites are satisfied before your plant ever arrives. This is well-established substrate science: the Dutch researcher Verhagen, whose work underpins the RHP substrate standard (RHP, short for Regeling Handelspotgronden or 'Potting Soil Trade Regulation', is the Dutch benchmark quality scheme for growing media), showed that raw coir carries high exchangeable potassium and sodium, and that calcium and magnesium from your feed get fixed onto the coir while potassium and sodium release, unless the coir is buffered first.
One distinction that trips people up: rinsing is not buffering. Rinsing washes out the loose, dissolved salts and lowers the EC. Buffering swaps the cations actually held on the exchange sites. Washing changes the EC but not what's clinging to the coir, so you need both: rinse to clear the loose salts, buffer to charge the sites.
Do you even need to buffer?
Not always. Here's the honest breakdown:
- Pre-buffered, reputable coco (ideally RHP-certified): usually no. Rehydrate, check the EC, and plant. Just don't confuse "washed" with "buffered": washing lowers the salts but doesn't charge the exchange sites, so "washed" coco still needs buffering.
- Raw or compressed bricks, cheap or unlabelled coco: assume yes.
- Reused coco: yes. As coco breaks down it exposes fresh exchange sites, so it needs re-buffering (more in our reusing and sterilising media guide).
The need is greatest in pure-coco hydroponic and container grows, and for young seedlings, which are the most sensitive to getting it wrong. When in doubt, buffer. It's cheap insurance against a frustrating deficiency later.
What you'll need
- Two containers: one with drainage holes sitting inside a solid one (fabric pots over a tray work too).
- Calcium nitrate and magnesium sulfate (Epsom salts), or a commercial cal-mag supplement.
- An EC/TDS meter and a pH meter. These are the real judges of when you're done.
- A pH adjuster (pH down), and clean water (see the water section).
- Gloves, a stirrer, and a bit of space, this is a wet job.
Method 1: the calcium nitrate method (the professional standard)
This is how commercial producers and the RHP standard prepare coir: wash it, charge the exchange sites with calcium (and magnesium), then wash it again. It's cheap in bulk and thorough.
- Rehydrate. Expand your brick in clean water (the pack will tell you the finished volume; a 5 kg brick makes roughly 60 to 75 litres). Break it up so it's evenly fluffy.
- Rinse. Flush the hydrated coir with plain, pH-adjusted water (around 5.8 to 6.0) and let it drain freely. This knocks down the loose salts before you buffer.
- Mix the buffering solution. Calcium nitrate at roughly 2 to 4 grams per litre of water is a sound starting point: a 2016 Sri Lankan study buffered coir pith at about 4 g/L, and commercial protocols sit in the same range. Add magnesium sulfate (Epsom salts) too, since calcium nitrate supplies no magnesium. There's no official ratio for buffering the two (it's calcium-led by design), and because calcium, magnesium and potassium compete with one another for uptake, you don't want to swamp one with the others (Currey, 2021). As a practical guideline rather than a hard rule, a cal-mag balance of roughly 3:1 to 4:1 calcium to magnesium is a sensible target, which is about where most commercial cal-mag products sit. Keep calcium the clear majority and you're in good shape.
- Soak. Saturate the coir completely and leave it in contact with the solution for a good stretch, commonly around 24 hours. The professional approach trickles treated water through slowly over about a day; at home, a long soak does the same job.
- Double-buffer (optional). For reused or lower-grade coir, drain and repeat with fresh solution. It's belt-and-braces, but it helps.
- Final rinse. Flush with plain, pH-adjusted water until the runoff EC drops into a safe range (see below). The buffering solution is deliberately high in EC, so this rinse is what protects your seedlings.
- Verify. Check the EC and pH of the runoff before you plant.
A note on the two salts: don't pre-mix calcium nitrate and magnesium sulfate as strong concentrated stocks, as they can react and cloud. At the dilute strengths used for buffering, mixing them in the bucket is fine.
Method 2: the cal-mag method (the easy way)
Most home growers use this one, and there's nothing wrong with it. A commercial cal-mag gives you calcium and magnesium together in a single bottle.
- Rehydrate and rinse exactly as above.
- Mix cal-mag at about 1.5 times your normal feed rate, then pH it to around 5.8 to 6.2. The solution will read a high EC, which is what you want.
- Soak the coir for 8 hours or more, overnight is ideal.
- Double-soak (optional) with fresh solution for thoroughness.
- Rinse with plain, pH-adjusted water until the runoff EC is in range.
- Verify EC and pH.
The trade-offs: cal-mag is simpler and gives you both nutrients at once, but it costs more per buffer than raw salts, and some cal-mag products carry a fair bit of nitrogen, so check the label if you're fussy about your ratios.
How to know it worked
Your meters are the honest judge, not the recipe.
- EC. Rinse until the runoff EC sits in a safe range. As a guide, most growing media should read under about 1.0 mS/cm (hydroponic systems can run a little higher), and well-buffered commercial coco can come in as low as 0.5. RHP's professional advice is to start a coir crop around EC 0.75 on their lab extract. For seedlings, aim lower rather than higher.
- pH. Aim for a runoff pH around 5.8 to 6.2.
- If the EC is still high, keep rinsing. Do not plant into high-EC coir, seedlings in particular will burn.
For the curious: the professional standard goes further than an EC meter. Dutch labs measure the exchangeable sodium and potassium directly, and the RHP benchmark for buffered coir looks for very low sodium (under about 1 mmol) and low potassium (under about 2 mmol). You don't need a lab at home; a good rinse and an EC meter get you there. That's just the bar the pros are hitting.
Water quality matters
- RO or soft water starts low in calcium and magnesium, so buffering and ongoing cal-mag matter more.
- Hard tap water already carries some calcium and magnesium, which reduces (but doesn't eliminate) what you need to add. Know your water; your local supply report or a cheap test tells you a lot.
- Use clean water to rinse, too. Verhagen found that the quality of the wash water changes how many salts are left on the coir, so it's not a step to do with dirty water.
After buffering: keep feeding cal-mag
Buffering is a strong start, not a whole-grow fix. Coco keeps a mild appetite for calcium and magnesium, and it exposes fresh exchange sites as it slowly breaks down, so most growers run a cal-mag supplement right through the grow (see the feeding section of the coco coir guide). The exception is a base nutrient formulated specifically for coco that already carries enough.
Spike's Tip: The recipe gets you in the ballpark; the EC meter tells you the truth. Buffer, then rinse, and don't plant until the runoff reads in range. Nearly every "I buffered and still got a deficiency" story ends with someone who trusted a number on a page instead of the meter in their hand.
Common mistakes
- Rinsing but not buffering. The classic. Washing drops the EC but leaves the exchange sites loaded with sodium and potassium.
- Assuming "washed" or "ready to use" means "buffered." It usually doesn't. Buffered coco says so on the bag.
- Planting straight after buffering. The buffering solution is high-EC; rinse it down first or you'll burn young roots.
- Forgetting magnesium. Calcium nitrate adds none, so pair it with Epsom salts, or use a cal-mag.
- Going overboard on calcium nitrate. A stronger solution doesn't buffer "harder"; the sites saturate at a sensible concentration, and too much just wastes product and nudges your pH around.
- Not verifying with meters. The whole method rests on that final EC and pH check.
A note on safe handling
Calcium nitrate and Epsom salts are fertiliser salts, so treat them sensibly: dissolve them fully, wear gloves, avoid breathing the dust, and store them dry, sealed, and away from kids and pets. Calcium nitrate is an oxidiser, so keep it clear of incompatible chemicals and follow the label. Give your buckets a quick sanitise (a weak bleach or hydrogen peroxide rinse, then rinse clean) before you start, so you're not seeding fresh media with old pathogens.
Frequently asked questions
Can I use cal-mag instead of calcium nitrate to buffer coco?
Yes. Cal-mag is the easy route and covers both calcium and magnesium in one bottle. Calcium nitrate (paired with Epsom salts for the magnesium) is the traditional, commercial method and works out cheaper in bulk. Both do the job.
Do I need to buffer "washed" or pre-buffered coco?
Washed coco, yes: washing lowers the loose salts but doesn't charge the exchange sites. Genuinely pre-buffered coco from a reputable, ideally RHP-certified brand, usually not, just rehydrate, check the EC and plant.
How long should I soak it?
For the cal-mag method, 8 hours or more (overnight is ideal). For the calcium nitrate method, commonly around 24 hours. The longer the contact, the more complete the exchange.
Do I still need cal-mag after buffering?
Usually yes, because coco keeps drawing a little calcium and magnesium throughout the grow. The exception is a coco-specific base nutrient that already includes enough.
Can I buffer coco after I've planted in it?
No. Buffer before planting. A high-EC calcium soak is no environment for live roots, so it's a before-you-plant job every time.
How do I re-buffer coco I'm reusing?
The same way, after you've cleared out the old roots and rinsed it. We cover the full reuse process in our reusing and sterilising media guide.
Everything you need to buffer, on one shelf
We stock coco, cal-mag (like our Green Planet Pro Cal), calcium nitrate, and the EC and pH meters that make buffering foolproof. Come and pick our brains in person at our Youngtown shop, or browse our growing media online. Found it cheaper elsewhere? Our Price Beat Guarantee has you covered, and orders placed in time go out with same-day dispatch.
References
- Verhagen, J. B. G. M. (1999). CEC and the saturation of the adsorption complex of coir dust. Acta Horticulturae, 481, 151-155. https://doi.org/10.17660/ActaHortic.1999.481.14
- Poulter, R. (2014). Quantifying differences between treated and untreated coir substrate. Acta Horticulturae, 1018, 557-564.
- 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
- RHP Horticulture. (n.d.). RHP advice: coir substrate. RHP. https://www.rhp.nl/
- Coir Board of India. (n.d.). Coir pith. Coir Board, Ministry of Micro, Small & Medium Enterprises, Government of India. https://coirboard.gov.in
- Kumarasinghe, H. K. M. S., Subasinghe, S., & Ransimala, D. (2016). Effect of coco peat particle size for the optimum growth of nursery plant of greenhouse vegetables. Tropical Agricultural Research and Extension, 18(1), 40-46. https://doi.org/10.4038/tare.v18i1.5324
- Currey, C. J. (2021). Nutrient antagonisms: The potassium, calcium and magnesium relationship (e-GRO Alert E614). e-GRO. https://www.e-gro.org/pdf/E614.pdf