Coco peat works well as the base of a container medium for forest and agroforestry seedlings, as long as you treat it as a low-nutrient, low-buffer substrate and feed accordingly. It fills root trainers and Hiko-type cells quickly, weighs a fraction of soil, holds together as a plug at lifting, and it doesn't carry the damping-off fungi and weed seed that come with topsoil. The trade-off is that seedlings on unfed coir finish smaller than on peat, and nitrogen and calcium are the two nutrients you'll be short of.
This article covers the container side. For the raw-material questions (EC, buffering, washing) see buffered vs unbuffered coco peat.
Why forestry nurseries moved from soil to coir-based media
Field surveys across tropical Africa, Asia and Latin America kept finding the same thing: seedlings that looked fine in the nursery grew badly after planting, and the cause traced back to poor root development in soil-filled containers. Clay-rich soils compact in a polybag, drain slowly and settle into an airless layer at the bottom. The standard advice now is an organic-based medium (compost, peat or coir), with soil, if used at all, kept to 10 to 30 percent of the mix.
| Property | Topsoil in a polybag | Coco peat based medium |
|---|---|---|
| Weight per cavity | High, and polybags run 1.5 litres and up | Low (coir bulk density is around 0.10 to 0.11 g/cm3 dry) |
| Drainage and air | Poor once compacted, airless base layer | Good, free draining, rewets easily |
| Uniformity | Varies by pit and season | Consistent within a graded batch |
| Weeds and pathogens | Present | Absent in clean, washed material |
| Root form | Spiralling, tap root at the bag base | Fibrous, trainable by ribs and air pruning |
| Nutrients | Variable, often locked up in clay | Low, you supply everything |
One Indonesian comparison put root trainer seedlings in a peat-based medium at about 20 percent more to produce than polybag seedlings in topsoil, with the gap closed by lower transport cost and better field survival. Coir plays the same role as peat in that sum, and it's local across most of the tropics.
What the trials say: coir versus peat and soil
The published record is thinner than for vegetables. Here is what exists.
| Species group | Set-up | Outcome on coir |
|---|---|---|
| Douglas-fir (North America) | 66 cm3 Styroblock cavities, 21 weeks, 2:1:1 coir:vermiculite:perlite against 2:1:1 peat:vermiculite:perlite, 150 ppm N weekly | Seedlings on 100 percent coir media were significantly smaller, with lower foliar nitrogen and calcium. Coir had pH 5.3 to 5.5 against 4.4 for peat, 45 to 200 times the potassium, and a CEC of 73 to 89 meq/100 g against 130. |
| Oaks (Mediterranean, three species) | Pure coir against peat, standard, potassium-enriched or phosphorus-enriched feed | Coir seedlings were smaller but still met the standard stocktype size. Root systems were proportionally larger and more fibrous. Extra potassium improved growth on both media. |
| Eucalyptus pellita (Southeast Asia) | Polytubes, 34 weeks, cocopeat, burnt rice hull and raw rice hull in 15 mixes | Cocopeat with burnt rice hull at 1:1 gave the best height, diameter and dry weight and the best root-medium cohesion when the plug was pulled. |
| Teak (South India) | 12 x 15 cm containers, soil:coir pith:vermicompost 2:1:1, 5 months | Five-month survival ranged from 68 to 100 percent across container types, with 90 percent in the polybag check. Height ranged from 17 to 32 cm, driven by container type rather than the medium. |
| Acacia, neem, Pongamia (Central India) | Hiko-type cells of 90, 150 and 300 cm3 | 90 cm3 was too small for a four-month crop. 150 cm3 was adequate for Acacia catechu and Pongamia, neem wanted 300 cm3. |
Coir alone, fed like peat, grows a smaller seedling. Coir fed for coir (more nitrogen, some calcium, less potassium) grows an acceptable seedling with a better root system. Blends with compost, vermicompost or burnt rice hull close most of the gap without changing the feed.
Coir alone or coir in a blend?
Pure coco peat in a small cell is a fast-draining, low-nutrient plug. Fine with fertigation. For a hand-watered agroforestry nursery, blend.
| Blend (by volume) | Where it fits | Notes |
|---|---|---|
| 100 percent coco peat | Fertigated conifer and eucalypt lines, miniplugs | Add nitrogen and calcium from sowing. Watch potassium build-up. |
| 3 coir : 1 compost or vermicompost | Broadleaf tropical species, hand-watered nurseries | Compost adds nutrients, buffering and CEC. Screen it and test its EC first. |
| 2 coir : 1 soil : 1 sand | Where a heavier plug is wanted for windy sites | Keeps soil under 25 percent. Weight goes up fast. |
| 2 coir : 1 vermiculite : 1 perlite | Direct peat replacement in temperate container lines | Same physical recipe as the standard peat mix. See coir with perlite and vermiculite. |
| 1 cocopeat : 1 burnt rice hull | Southeast Asian eucalypt and acacia nurseries | Rice hull char raises air porosity and pH, helps plug cohesion. |
Whatever you blend, aim for 60 to 80 percent total porosity and 20 to 35 percent air-filled porosity (some greenhouse recommendations go to 45 to 50). Fine pith alone can miss the air target in a short cell, so a coarser grade helps. See particle size grades.
Cavity volumes and how much coir you need
Cavity volume decides your medium order and your bench density.
| Container type | Typical cavity volume | Seedlings per m2 (approx.) |
|---|---|---|
| Miniplug trays | 10 to 25 ml | - |
| Hiko-type trays (V93 is the common Indian size) | 90 to 150 ml, up to about 530 ml | 575 at 90 ml, 225 at 150 ml |
| Root trainers (book and sleeve type) | 55 to 1,100 ml, with 150 and 300 ml common | 144 at 300 ml |
| Ray Leach style cells | 49 to 164 ml | - |
| Styroblock cavities (conifer trade) | 40 to 490 ml, with 57 and 65 ml the classic reforestation sizes | - |
| Polybags | 1,500 to 15,000 ml | - |
To size the order, multiply cavity volume by the number of cavities and add 15 to 20 percent for settling and spillage. A 5 kg block is usually quoted at 60 to 80 litres of loose medium depending on compression and moisture, which fills 400 to 500 cells of 150 ml. The same block fills only 40 to 50 polybags, which is why the move to small cells and to coir tends to happen together. See the blocks page for formats and coir for container nursery stock for larger pots.
Fill moist, not wet. Fluff the hydrated coir, fill level, tap the tray and top up. Don't press it in. A compacted plug loses the air porosity that was the point of switching.
Fertigation and EC for seedlings
Coir has low CEC, so there's little buffer between feeds. Check EC of the medium, not just the tank.
| Growth phase | Nitrogen in fertigation | Irrigation trigger | Notes |
|---|---|---|---|
| Establishment (germination to first true leaves) | 25 to 75 ppm N | Keep surface moist | Low feed, high salt sensitivity, damping-off risk rises with high N |
| Rapid growth | 100 to 150 ppm N, ammonium acceptable | Water at about 85 percent of saturated tray weight | Highest feed, watch shoot stretch |
| Hardening | 25 to 50 ppm N, nitrate form, calcium nitrate ideal | Water at about 70 percent of saturated tray weight | Raise potassium relative to N |
For the medium itself, EC guidelines for soilless media run: under 1.2 mS/cm low, 1.2 to 2.5 normal, 2.5 to 3.0 high, 3.0 to 4.0 excessive and above 4.0 lethal. Seedlings in small cells should sit at the low end of normal. Irrigation water should be under 0.5 mS/cm, with sodium below 50 ppm and chloride below 70 ppm. Salt in the plug doubles when the medium dries from 50 to 25 percent moisture, so EC problems show up first in the driest trays on the bench edge.
Two coir-specific points. Coir carries a lot of potassium, so the feed can carry less K than a peat programme. It is low in calcium and nitrogen, so calcium nitrate does double duty. Where coir seedlings came out small in trials, low foliar N and Ca were the reason. In-crop management is covered in pH and EC management.
Hardening and moisture before outplanting
Start hardening at 75 to 80 percent of target height. For tropical species it runs 4 to 12 weeks, timed to the rains. The tools are the same as for peat-grown stock: fewer irrigations, less nitrogen, nitrate instead of ammonium, shade off, and trays allowed to dry to about 70 percent of saturated weight.
Coir rewets without the hydrophobic sulk of dried peat, so a tray that dried too far on a hot afternoon recovers at the next irrigation. It is also easy to overdo, because coir looks dry on top while the root zone is still moist. Weigh a marked tray rather than judging by eye.
A quality check used in Indian root trainer nurseries is the sturdiness quotient: height in cm divided by collar diameter in mm. Lower is sturdier. Pair it with a look for a lignified brown stem and leaves over the top three quarters of the shoot.
Root plug integrity at lifting
A plug that falls apart at extraction is the main objection to pure coir in small cells. It is fixable.
- Irrigate one to two days before lifting so the plug is at container capacity, not saturated. A waterlogged plug is heavy and smears.
- Don't lift early. A coir plug holds together because roots bind it. In a 150 ml cell that usually means the full four-month crop Indian root trainer nurseries run between March and the monsoon.
- Use cells with vertical ribs and an open base so roots air-prune instead of circling.
- Pull test: lift a few seedlings per tray by the stem. If more than a handful drop medium from the lower third, the batch isn't ready.
- Fine roots dry out first. Keep lifted plugs shaded and moist, never saturated, through transport.
A coarser grade or a compost fraction binds a plug faster than fine pith alone. If the monsoon fixes your lifting date, that's an argument for a blend.
Specification for a nursery tender
A tender that asks for "cocopeat, good quality" gets the cheapest unwashed dust in the district. Write it like this.
| Item | Specification | Why |
|---|---|---|
| Material | Coco peat (coir pith), screened, free of long fibre, stones and plastic | Fibre bridges in the filler, debris blocks cavities |
| Washing | Water washed, EC of 1:1.5 volume extract below 1.0 mS/cm, stated per lot | Removes sodium and chloride that stunt seedlings |
| pH | 5.5 to 6.5 | Range for container tree nurseries |
| Particle size | Mostly 0.5 to 3 mm for cells under 150 ml, coarser fraction allowed for larger cells | Air porosity in shallow cells |
| Condition on delivery | Compressed blocks, dry to the touch, no visible mould, wrapped | Storage and hydration behaviour |
| Expansion | Litres of loose medium per block, stated, with a sample to check | Converts to cells per block |
| Chemical additives | None, or buffered with calcium nitrate, stated either way | Decides your calcium and K programme |
| Documentation | EC, pH and moisture per lot, batch code on every block | Traceability across a multi-year planting programme |
Ask for samples from the production lot and run your own EC and expansion check before the crop.
CVM Fiber and Industries manufactures coco peat blocks, briquettes and husk chips in Kanyakumari, Tamil Nadu, India. Our coco peat is washed with water to reduce EC, with no calcium nitrate or other chemicals, so it is unbuffered and you set the calcium programme yourself. If you're writing a specification for a forestry or agroforestry nursery, or need a custom blend with chips for larger cells, contact us with your cavity sizes and seedling numbers.
FAQ
Can I grow forest seedlings in 100 percent coco peat?
Yes, if you fertigate. Trials on conifers and oaks show seedlings on pure coir finish smaller than on peat when fed the same programme, mainly because coir is low in nitrogen and calcium and has a lower cation exchange capacity. With a coir-specific feed the size is acceptable and the root system is more fibrous. Hand-watered nurseries without fertigation should blend with compost or vermicompost.
What ratio of coco peat to vermicompost should a root trainer nursery use?
Around 3 parts coco peat to 1 part screened compost or vermicompost by volume is a workable starting point, and teak nurseries in Kerala have used soil, coir pith and vermicompost at 2:1:1. Test the EC of the compost first, since manure-based vermicompost can push a small plug over 2.5 mS/cm. Adjust after one crop rather than copying a ratio blind.
How much coco peat do I need per root trainer cell?
Take the cavity volume and add 15 to 20 percent for settling. A 150 ml cell therefore takes about 175 ml of loose, hydrated medium, so a 40-cell tray needs around 7 litres. A 5 kg block yields roughly 60 to 80 litres, which fills 8 to 11 such trays.
Which cavity volume is right for tropical broadleaf seedlings?
Indian trials with Acacia catechu, Pongamia and neem found 90 ml too small for a four-month crop. 150 ml gave good quality stock for the first two, and neem needed 300 ml. Conifers and eucalypts tolerate smaller cells than large-leaved broadleaves because they intercept less light and water per plant.
What EC should the medium be for tree seedlings in coir?
For soilless media, 1.2 to 2.5 mS/cm is the normal range, under 1.2 is low and above 3.0 is excessive. Small seedlings in small cells should sit at the low end of normal. Check the driest trays, because salt concentration in the plug roughly doubles as the medium dries from 50 to 25 percent moisture.
Why does my coir plug fall apart when I lift the seedling?
Usually the seedling is too young and roots haven't bound the medium, or the coir is very fine pith with no structure, or the plug is either bone dry or waterlogged. Irrigate one to two days before lifting, wait until roots show at the drainage slot, and consider a coarser grade or a compost fraction. Ribbed cells with an open base help roots fill the whole plug.
Do I still need to harden seedlings grown in coco peat?
Yes. Hardening is about the plant, not the medium. Begin at 75 to 80 percent of target height, run 4 to 12 weeks for tropical species, cut nitrogen to 25 to 50 ppm in nitrate form, remove shade and let trays dry to about 70 percent of saturated weight between irrigations. Coir rewets easily after a dry-down, which makes the process more forgiving than peat.
Is coco peat cheaper than soil for a forestry nursery?
Per litre it costs more than dug topsoil. Per seedling delivered to the planting site it often costs less, because coir goes into small cells instead of 1.5 litre polybags, trays weigh a fraction of bagged soil on the truck, and survival after planting is better.