01 · Direct answer.
Choose by the process the crop requires, not by the name. Natural (unwashed) measures 0.8 to 1.5 mS/cm (1:5) and suits tolerant crops, landscaping and substrate manufacturers who correct EC in their blend. Washed goes through 2 to 3 freshwater cycles, ends below 0.7 mS/cm and suits ornamentals, forestry seedlings and soilless vegetables. Buffered is washed and then soaked in calcium nitrate, ends below 0.5 mS/cm and is the grade for strawberry, tomato, flowers and seed sowing.[4] All three grades are for sale.
| Grade | Process | EC (1:5) | Suited crops |
|---|---|---|---|
| Natural | None: shredding and screening, no washing, no additives | 0.8-1.5 mS/cm | Coffee, clonal eucalyptus, citrus, landscaping, leafy vegetables |
| Washed | 2 to 3 cycles of freshwater immersion and drainage | < 0.7 mS/cm | Potted ornamentals, forestry seedlings, soilless vegetables |
| Buffered | Washed, then soaked in calcium nitrate and rinsed | < 0.5 mS/cm | Strawberry, tomato, flowers, orchids, seed sowing, organics |
Bands and crops as on Carve's public Coir Pith data sheet. EC measured per lot; grade defined in the contract.
02 · What washing removes and what it does not.
Dry coconut husk carries potassium (1.60 %), chlorine (1.80 %) and sodium (0.38 %) in its own structure, which is why raw EC ranges from 0.4 to 6.0 mS/cm according to EMBRAPA.[1] These salts are not all in the same place, and that is what separates the grades:
- Chlorine and the salts dissolved in the pore water leave with fresh water. Chlorine, according to Romero, is the easiest to wash out.[2]
- The sodium and potassium held in coir's organic complex do not leave with water: "water alone does not have the capacity to displace" these ions. Only calcium or magnesium does.[2]
- Romero describes four levels on the market: unwashed, washed, super-washed and treated with calcium or magnesium, and advises buying coir "with a first name and a surname": the first name is the particle size, the surname is the salt level.[2]
- The washing target cited by EMBRAPA for dry coconut husk is EC below 1.0 mS/cm.[1]
A lower starting point means fewer cycles. Carve's husk is dry mature husk, rain-aged inland and never retted in brackish water, and it is washed with artesian well water at 64 to 480 µS/cm. Low EC is reached in 2 to 3 freshwater cycles, against five or more documented for high-salt material in the literature.[6] EC bands by crop are detailed in Coir pith EC by crop.
03 · How Washed is made.
At Carve, the pith is washed after shredding and rotary screening.[4] The process, in order:
- The tank receives fresh water until the pith is covered. The well water is measured before it goes in.[5]
- Immersion with agitation, then drainage through a screen. The first water comes out dark, which is normal: it carries tannins and dissolved salts.[5]
- The EC of the drainage water is measured each cycle. With new fresh water the cycle repeats: 2 to 3 cycles in total, according to the reading.[4][5]
- The pith is pressed to remove excess water and dried to shipping moisture, 18 % at most.[4]
- Once dry, the lot is measured in the 1:5 extract. That is the value on the lot report, and the contracted limit decides whether the lot ships.[4]
04 · How Buffered is made.
- First the full wash, so that cheap water removes the soluble salts before calcium goes in.[5]
- Then immersion in a calcium nitrate solution at 12 to 18 kg per tonne of pith, with 24 hours of contact and agitation during the period.[4][5]
- Calcium, with a +2 charge, occupies the exchange sites and displaces potassium and sodium, which move into the solution.[2]
- Two rinses with fresh water carry away the displaced potassium and sodium. Without this rinse the salts would stay with the product.[5]
- Drainage, pressing, drying and the same 1:5 test as the lot report.[4]
Two points from Romero matter to anyone who fertigates: the treatment uses calcium or magnesium, not both, and the calcium held in place of sodium and potassium is not available to the plant, so it does not count in the nutrient solution.[2] David Cadena sums up the practical effect of well-prepared coir as a management buffer for EC and pH that synthetic substrates do not offer.[3]
05 · When Natural is the right choice.
- Landscaping, mulch and bed cover: high EC tolerance, direct use, any grade.[4]
- Substrate manufacturers: they set an EC ceiling in the contract and correct EC in the final formulation. The husk's natural potassium is why they cut potassium in the blend.[1][4]
- Coffee, clonal eucalyptus, citrus and leafy vegetables, with a limit in the contract.[4]
Whatever the grade, the lot report carries the same five tests. What changes is the contracted ceiling: see Coir pith lot report (COA). Company data are on Company facts.
06 · Frequently asked questions.
Is washed coir pith the same as buffered?
No. Washed goes through 2 to 3 freshwater cycles and ends below 0.7 mS/cm (1:5); Buffered is washed and then soaked in a calcium nitrate solution, which displaces the potassium and sodium held on coir's exchange sites, and ends below 0.5 mS/cm. Both lower EC, but only buffering removes the salt that water cannot reach.
How many wash cycles does coir pith get?
Two to three cycles of freshwater immersion and drainage. The EC of the drainage water is measured each cycle, and the lot moves on to pressing and drying when it reaches the target. Once dry, the lot is measured again in the 1:5 extract, and that is the value that goes on the lot report.
Does washing remove all the salt from coir pith?
No. Water removes chlorine and the salts dissolved in the pore water, but it does not displace the sodium and potassium held in coir's organic complex, according to Adalberto Romero. Only calcium or magnesium does that. This is why a washed lot can read a low EC and still hold a potassium reserve that appears weeks later, during fertigation.
Can I buy Natural coir pith and wash it myself?
Freshwater washing lowers EC, and the target cited by EMBRAPA is below 1.0 mS/cm. What washing on the farm does not do is buffering: without calcium or magnesium, the sodium and potassium held in the organic structure stay there. For landscaping, substrate manufacturers and tolerant crops that does not matter; for strawberry, flowers, orchids and seed sowing, the recommended grade is Buffered.
What changes on the lot report between Natural, Washed and Buffered?
The tests are the same (EC 1:5, pH, moisture, bulk density and particle size) and are run on every lot. What changes is the acceptance limit fixed in the contract: 0.8 to 1.5 mS/cm for Natural, below 0.7 for Washed and below 0.5 for Buffered. A lot outside the contracted limit does not ship.
07 · Sources.
- EMBRAPA Tabuleiros Costeiros, Comunicado Técnico 226 (COT-226-19): raw EC 0.4-6.0 mS/cm, washing target below 1.0 mS/cm, composition K 1.60 % / Cl 1.80 % / Na 0.38 % of dry husk.
- Ing. Adalberto Romero webinar (Science Fetti / El Semillero, Colombia, 2025): four salt levels, "first name and surname", water does not displace Na/K from the organic complex, Ca or Mg treatment (one of the two), bound calcium not available to the plant, chlorine as the easiest salt to wash out.
- Lic. David Cadena webinar (Mexico, hosted by Riego Rotoplas, 2026): coir as an EC and pH management buffer.
- Carve public specification: Coir Pith and Quality pages: process by grade, EC bands, calcium nitrate dose, maximum moisture 18 %, measurement per lot.
- Carve washing and buffering operating procedure: order of steps, drainage-water measurement, 24-hour contact, double rinse.
- Carve raw-material description on Import Coir from Brazil (dry inland husk, never retted; artesian well water at 64-480 µS/cm; 2-3 cycles); Raviv, M., Lieth, J.H. & Bar-Tal, A. (2019), Soilless Culture, 2nd ed., ch. 8 (five or more cycles for high-salt material).