The short answer: the standard pro-tray method for tomato, chilli, brinjal and brassicas fills 98-cell trays with washed coco peat, either on its own with neem cake and bio-inputs or as a 3:1:1 mix with vermiculite and perlite. Trays are stacked under polythene for 3 to 6 days until the seed sprouts, then moved to a shade-net house, fed, hardened and dispatched at roughly 21 to 30 days. Cucurbits go out sooner, in bigger cells.
The media: 3:1:1 and the alternatives
The mix most often quoted for pro trays is 3 parts coco peat, 1 part vermiculite, 1 part perlite by volume. That's 60 % coir, 20 % vermiculite, 20 % perlite. Coir holds the water, vermiculite adds a little more water and some nutrient-holding capacity, and perlite keeps the cell from going sour when someone overwaters.
Published trials of 3:1:1 against plain coir for vegetable plugs are hard to find. Treat it as a practical recipe, not a proven optimum. Two other mixes are better documented:
| Mix | Recipe | Notes |
|---|---|---|
| Coir with neem cake and bio-inputs | 300 kg sterilised coco peat + 5 kg neem cake + 1 kg each of Azospirillum and phosphobacteria | The university-recommended protray mix in Tamil Nadu. Enough for about 238 trays. |
| Coir with compost | Equal weights of coco peat and compost, plus 100 g each of Trichoderma and Pseudomonas fluorescens per 5 kg of coir | Used by village nursery entrepreneurs. Rest it in shade for a few hours before filling. |
| 3:1:1 coir, vermiculite, perlite | By volume | More open and more uniform. Costs more per tray because of the minerals. |
If you add compost, make it mature and screened. Some guides keep compost out of germination mixes altogether because it can carry damping-off organisms.
And one caution on coir itself. In a two-season shade-net trial in Punjab with brinjal and chilli in 98-cell trays, a vermiculite, perlite and coco peat mix at 1:1:2 gave the lowest germination of six media: about 60 % for brinjal and 40 % for chilli, against 71 % and 66 % for a vermiculite, perlite and vermicompost mix. Coir is not automatically the winner.
General blending rules are in coir, perlite and vermiculite mixes.
Trays and medium per hectare: the arithmetic
Work backwards from the farmer's plant population. These are the published figures for hybrids in paired-row planting, all in 98-cell trays:
| Crop | Spacing (cm) | Seedlings per ha | Trays per ha (98-cell) | Spare cells |
|---|---|---|---|---|
| Tomato | 90 x 60 x 60 | 23,334 | 238 | none (238 x 98 = 23,324) |
| Chilli | 90 x 60 x 45 | 29,000 | 300 | 400, about 1.4 % |
| Brinjal | 90 x 60 x 75 | 18,700 | 200 | 900, about 4.8 % |
| Cabbage | 60 x 45 x 45 | 28,333 | 290 (our arithmetic) | 87 |
The spare is thin. Plan sowing on what you actually get out of a tray, not on 98, and allow for the farmer who wants extras for gap-filling.
For medium, the figure quoted is about 1.2 kg per tray (1.25 kg in the cabbage guidance), and that is moist coco peat. The same programmes fill trays at 300 to 400 % moisture, so if that's on a dry-weight basis, 1.2 kg holds roughly 0.24 to 0.3 kg of dry coir. So for one hectare of chilli, budget around 360 kg of moist medium. Weigh a few of your own filled trays and use that number.
On labour, a dibbler-seeder built for 98-cell trays sowed 150 trays an hour in trials, against about 10 by hand.
Cell size by crop
| Crop | Usual tray | Why |
|---|---|---|
| Tomato, chilli, brinjal | 98-cell | Standard for solanaceous crops at 3 to 4 weeks |
| Cabbage, cauliflower | 98-cell (128-cell also works for cauliflower) | Small seed, compact plug |
| Bitter gourd, bottle gourd, watermelon | 50-cell | Cucurbits dislike crowding and root-bind fast |
| Cucumber, squash, melons | 48, 50 or 72-cell | Larger cells give more root and faster establishment |
Cucurbits grow fast and sulk if held. Trial results on watermelon cell size are mixed, so the safe rule is big cells and a short time in the tray.
Sowing and germination
- Fill loosely and tap. Fill cells with damp medium, tap the tray to settle it and strike off level. Don't press.
- Dibble and sow. Make a depression about 0.5 cm deep in the centre of each cell, sow one seed per cell and cover with a little coco peat.
- Don't water yet. Medium filled at 300 to 400 % moisture needs no irrigation until the seed sprouts.
- Stack and cover. Stack about 10 trays, cover the stack with polythene or a moist jute sack, and keep it in a shaded spot.
- Check daily and unstack on time. Chilli, tomato and cauliflower sprout in about 3 to 4 days. Bitter gourd takes 6 to 7. Pull each tray as soon as you see sprouting, or the seedlings stretch.
This is where new nurseries lose most. One first-season operator lost 5,000 seedlings at the germination stage alone.
With a germination chamber, tomato wants a media temperature of 21 to 27 °C and 100 % humidity until the root emerges, which takes 3 to 5 days. Trays usually need only 36 to 48 hours in a heated chamber. Take them out as soon as the radicle shows, because continuous heat makes leggy seedlings.
The shade-net house
After germination, trays go onto raised beds inside the net house. The standard setup is 50 % shade net overhead and 40 or 50 mesh insect-proof nylon net on the sides, to keep out the whiteflies and thrips that carry viruses into tomato and chilli. Give the floor about a 2 % slope so water doesn't pool under trays.
Once seedlings are up, drop humidity to normal ambient levels, roughly 50 to 80 %, and give them light.
Watering and feeding
Water daily with a fine rose can, adjusting to the weather. Sunny days during emergence may need two light waterings.
Coco peat carries almost no nitrogen, so feeding is not optional. The common nursery schedules use 19:19:19 water-soluble fertiliser:
| Schedule | Dose | Timing |
|---|---|---|
| Single drench | 0.5 % (5 g/L) | 18 days after sowing |
| Lighter drench | 0.3 % (3 g/L) | 18 days after sowing |
| Two sprays | 0.3 % (3 g/L) | 12 and 20 days after sowing |
Do the sum before you mix. 19:19:19 at 5 g/L carries about 950 ppm of nitrogen, and 3 g/L about 570 ppm. Extension guides for transplants suggest about 50 ppm N at the first true leaf, then 100 to 150 ppm weekly. A strong one-off drench works, but you can split the same fertiliser into lighter, more frequent feeds starting at the first true leaf, which keeps you closer to those extension rates. More on early feeding in our seed germination guide.
Seedling age at dispatch
| Crop | Indian pro-tray guidance | Extension guidance (cooler climates) |
|---|---|---|
| Tomato | 25 days, up to 30 | 5 to 7 weeks |
| Chilli | 21 to 30 days | 5 to 7 weeks (8 to 10 also quoted) |
| Brinjal | 21 to 30 days | – |
| Cabbage | 25 days in trays (30 to 45 days quoted for bed nurseries) | 5 to 7 weeks |
| Cauliflower | 25 days in trays (40 days also quoted) | 5 to 7 weeks |
| Cucumber | – | 2 to 3 weeks |
| Squash, watermelon | – | 3 to 4 weeks |
Warm net houses grow plugs faster than cold-country spring greenhouses. What matters is the plug: roots should fill the cell from top to bottom so it pulls out whole, and the plant shouldn't be root-bound or stretched.
Hardening
Before dispatch, cut water and cut shade. The brassica guidance is to withhold irrigation for 4 to 6 days before planting. Other guides harden gradually over 5 to 10 days. In practice: out from under the 50 % net for the last week, and water only when plugs begin to lighten.
Where nurseries lose trays
Damping-off. Caused by Pythium, Rhizoctonia and Fusarium, and favoured by cool, wet, badly drained conditions. Before emergence it looks like poor germination, after it like a stem lesion and collapse. Use clean seed and clean water, keep hose ends off the floor, avoid splashing from tray to tray, and drop humidity after emergence. Don't reuse trays that held a diseased batch. Small cells are hard to disinfect.
Fungus gnats. Larvae feed on young roots and open wounds for Pythium and Fusarium, and adults can carry spores between trays. Lay yellow sticky cards flat at medium level and change them weekly. The fix is drier production. More on that in mould, algae and fungus gnats in coco coir.
Transport and handover
Water trays thoroughly before they leave the yard. Don't keep seedlings in a closed vehicle or shed for more than a day or two. Tomato plugs can be held for up to two weeks if they must be, but keep them above 10 °C, raised off the ground, and feed them if planting slips beyond 5 to 7 days. Tell farmers to plant early in the morning or late in the evening to cut transplant shock.
What to specify when buying coco peat
Batch-to-batch consistency matters more than any single number. Ask for:
- Washed, low-EC coir, with EC and pH reported and the test method named.
- Buffered or unbuffered, stated clearly. Either can work for nurseries. See buffered vs unbuffered for the trade-offs.
- A fine grade with little long fibre, so 98-cell trays fill evenly and the dibbler doesn't drag. Our guide to particle size grades shows how to check this with a sieve.
- The format: 5 kg blocks for volume, 650 g briquettes for small nurseries without a hydration tank.
- A sample first. Sow two or three trays of your main crop next to your current medium before you commit to a season's stock.
CVM Fiber and Industries makes coco peat in Kanyakumari, Tamil Nadu, India, from husk sourced across several districts. It comes as 5 kg blocks, 650 g briquettes and custom blends. It's washed with water to bring EC down, with no calcium nitrate or other chemicals, and is not buffered. If you run a seedling nursery and want to trial it in your trays, get in touch.
FAQ
What is the best cocopeat mix for pro tray nurseries?
Washed coco peat with neem cake and bio-inputs, or a 3:1:1 mix of coco peat, vermiculite and perlite by volume, are the usual choices. The quality of the coir batch and your feeding schedule matter more than the exact ratio.
How much cocopeat does one 98-cell pro tray need?
About 1.2 to 1.25 kg of moist coco peat per tray. Weigh a few of your own filled trays, because fill density varies.
How many pro trays do I need for one hectare of chilli or tomato?
About 300 trays of 98 cells for 29,000 chilli seedlings, and about 238 trays for 23,334 tomato seedlings in paired rows. Sow extra trays to cover empty cells and culls.
How long should pro trays be stacked after sowing?
Usually 3 to 6 days under polythene or a damp jute sack, depending on the crop. Check daily and move each tray to the net house as soon as it sprouts, or the seedlings stretch.
At what age are pro tray seedlings ready for sale?
In warm net houses, tomato, chilli, brinjal, cabbage and cauliflower are usually ready at 21 to 30 days. Cucurbits are ready sooner. The plug is ready when roots hold the medium together from top to bottom.
Should I add vermicompost or compost to cocopeat for seedlings?
Many nurseries do, for nutrients and biology. Compost can also carry damping-off organisms, so use only mature, screened material and keep feeding.
Why are my seedlings dying at the base in pro trays?
That's almost always damping-off, helped by wet medium, high humidity and splashing. Water less, lower humidity after emergence, use clean water and throw out affected trays.
Can I use unbuffered cocopeat for a vegetable nursery?
Yes, if it has been washed well and tests low in EC. Feed from the first true leaf with a fertiliser that includes calcium and magnesium, and test a few trays of each new batch first.