The short answer: coco coir works as a crate and bed substrate for forcing tulips, lilies and other cut-flower bulbs, provided it's washed to a low EC and you treat it like any other soilless mix: 5 to 8 cm under the bulb, a damp but draining profile, a rooting room that steps down from 9 °C, and clean crates every batch. Most Dutch tulips are now forced on water, so coir's place is the substrate-forced share: lilies, hyacinths, iris and the tulip growers who want the brighter colour and longer stems a solid medium still gives.
Key figures
- Tulips forced on water in the Netherlands: quoted at 85 to 90% of the crop.
- Tulip crate: 60 bulbs of 12/+ in ten rows of six, up to 100–105 bulbs of 11/12. About 7.5 cm of substrate under the bulb, 5–8 cm over it, tips showing.
- Rooting room: start at 9 °C (or 5 °C), step down 2 °C at a time to 0 °C, never below −2 °C. Total cold 12–18 weeks depending on cultivar.
- Tulip feed: EC 1–1.5 mS/cm (1:2 extract), pH 5.5–6.8 depending on the guide. Water-forced tulips are filled at EC 1.7–2.0 and run at 1.5.
- Salt: tulips tolerate up to 5 mmol/l sodium chloride without quality loss. The Dutch reuse limit is 5 mmol Na/l for tulip and 3 mmol Na/l for lily and iris.
- Lily pH: 6–7 for Asiatic and longiflorum, 5.5–6.5 for Oriental, 6.8–7.2 where fluoride scorch is a risk. Avoid perlite and superphosphate.
Water or substrate? Where coir fits
Tulip forcing on water started at scale in the Netherlands in 1993 and has taken most of the crop since. You'll see 85% quoted by bulb exporters and 90% in trade reporting. The reasons were never about flower quality. A filled water tray weighs about 7 kg against 20 kg for a soil crate, needs roughly half the cooling space, can be used two or three times in a season, and avoids buying and disposing of peat. Energy per ten-stem bunch has been put at 7.97 MJ in soil, 7.03 MJ on standing water and 5.80 MJ in ebb-and-flood.
Substrate forcing still has a case, and it's the one coir has to make:
| On water | In substrate (peat or coir) | |
|---|---|---|
| Colour | Slightly duller | Brighter, in growers' experience |
| Stem length | Shorter, stems stretch more in the vase | Longer, firmer stems |
| Bulb size | 10–12 cm preferred. Bulbs over 14–15 cm get Pythium and grow too soft | Any size, including the big 12/+ that cut-flower growers want |
| Disease | Less Fusarium. Pythium if bulbs are damaged at planting | Fusarium and basal rots if the crate isn't clean |
| Greenhouse temperature | About 17 °C, 1–2 °C cooler than soil | 18–19 °C |
| Time in greenhouse | 3–3.5 weeks | 3–3.5 weeks |
| Vase life | Same | Same |
| Rooting time before the greenhouse | 2–6 weeks at 7–9 °C | Planted at least 6 weeks before forcing, often the whole 12–18 weeks |
| Labour | Lighter, cleaner. Weekly planting | Heavy crates, autumn planting peak |
Cut lilies are grown in greenhouse soil or in crates of substrate, and crates have gained because soil needs steaming or chemical disinfection every year. Hyacinths and Dutch iris go both ways: in hyacinth trials water forcing finished 1 to 5 days earlier but the substrate-forced stems were longer. Compared with roses and gerbera on coir slabs, bulbs are simple. One short crop, then the substrate comes out.
Setting up a tulip crate in coir
Root formation depends on what's under the bulb, not on how deep it's buried. That's the one rule to carry from peat to coir.
| Step | Figure |
|---|---|
| Crate | Short tulip crate, not the taller lily crate. Line the base with paper so fine coir doesn't fall through |
| Substrate under the bulb | About 7.5 cm (3 in), pre-moistened to a wrung-out sponge |
| Bulb count | 60 of 12/+ in ten rows of six. 60–70 is the usual range. Up to 100–105 of 11/12 |
| Spacing | Almost touching, like eggs in a carton |
| Cover | 5–8 cm, or leave the top third exposed. Tips visible after watering |
| Watering in | Heavy, then keep moist. Top crates in a stack dry first |
| Mix pH | 5.5–6.5 from one grower guide, 6.2–6.8 from an extension service. Fresh washed coir sits inside both ranges |
| Mix temperature at planting | If the mix was heat-treated, cool it to 13 °C or lower before planting |
Dutch forcers plant into peat and top the crate with coarse sand. With coir, a coarser grade on top does the same job: it holds the bulbs upright when crates are moved and drains fast so the nose of the bulb stays dry. Grades are explained in coco peat particle size grades. Bed planting follows the same depth: 2–5 cm of cover, about 250 bulbs per m² for 5 °C-treated bulbs, soil at 9 °C or lower at planting, and at least six weeks of cold in the ground before the house is warmed.
Tulips are light feeders and extra nitrogen shortens them. Start feeding once shoots are 5–6 cm, with a 2:1 calcium nitrate to potassium nitrate mix, or 200–250 ppm N by injection, and keep the extract EC between 1 and 1.5 mS/cm. Bed growers apply 50 g calcium nitrate per m² once roots have formed.
The rooting room
Bulbs only register cold if the medium is moist, and dry peat in a crate is the classic sign of uneven cooling. Coir rewets more easily than dry peat, a point in its favour in a stack that's sat for 14 weeks, but it also drains more freely, so check the bottom of the crate, not the top.
| Stage | Temperature | Notes |
|---|---|---|
| Planting and rooting | 9 °C, sometimes 5 °C. US guides give 4–9 °C for 2–3 weeks in the dark | RH 90–95% in the rooting cell. Dry bulbs in store want about 80% to stop Penicillium |
| Step-down | Drop 2 °C at a time to 0 °C | Holds shoot stretch so sprouts don't jam against the crate above |
| Cold storage | 0 to 1 °C, never below −2 °C | Total cold 12–18 weeks by cultivar. Unplanted dry storage no more than 8 weeks or roots lift the bulbs |
| Into the house | 14–18 °C. 60 °F gives flowers in about 4 weeks | Above 20 °C the risk of topple rises |
Ethylene in the cold store should stay at or below 0.1 ppm. One rotting bulb produces it, so stacked crates get checked, not just the outer rows.
Lilies in coir crates and beds
Lilies are planted year-round, root at warmer temperatures than tulips, and grow the stem roots that feed the plant in the top layer of the medium a few weeks after planting. That top layer has to stay moist without going sour.
Pre-rooting is standard. Open the crate for up to seven days at 9–14 °C so roots start before the bulbs go into warm soil, or plant into crates and root them in a cold room at 8–14 °C, dropping to 5 °C in autumn. Frozen bulbs defrost for a week at 8–10 °C. Cover with 6–8 cm in winter and 8–10 cm in summer. Keep soil temperature at 15 °C or below in warm months and the house at 15–20 °C, not above 20–25 °C.
Densities by hybrid group and bulb size:
| Bulb size | Asiatic / m² | Oriental / m² | Oriental per crate | OT per crate | LA / m² | Longiflorum / m² |
|---|---|---|---|---|---|---|
| 10/12 | 60–70 | – | – | – | – | 55–65 |
| 12/14 | 55–65 | 55–65 | 15 | – | 50–60 | 45–55 |
| 14/16 | 50–60 | 45–55 | 12 | 12 | 40–50 | 40–50 |
| 16/18 | 40–50 | 40–50 | 10 | 10 | 40–50 | 35–45 |
| 18/20 | – | 35–45 | 8 | 8 | – | – |
| 20/22 | – | 30–40 | 6 | 6 | – | – |
| 22/+ | – | 25–35 | 5 | 5 | – | – |
The crate counts are for a standard 60 × 40 cm bulb crate, which is how the per-m² and per-crate columns reconcile.
Coir and lilies have been trialled directly. LA hybrids forced in 60 × 40 × 15 cm crates holding 20 litres of medium gave 99.8 cm stems in pure coco peat against 84.6 cm in garden soil, 5.4 buds per stem against 3.9, and stem roots more than twice as long. The coco peat had 57% porosity against 25% for the soil. Lily stem roots want air. A 1:1 coir and sand mix came in between.
pH, EC and the fluoride question
Lily pH targets depend on the group: 6–7 for Asiatic and longiflorum hybrids, 5.5–6.5 for Orientals and speciosum. Above pH 7 lilies go chlorotic between the veins from iron lock-out, and a chelated iron drench or spray fixes it. Fresh coir at pH 5.5–6.5 lands in range without lime for Orientals and needs a little lime for Asiatics.
Some lily cultivars scorch from fluoride. The advice for those is a pH of 6.8–7.2, plenty of calcium, and no superphosphate or perlite in the mix, since both carry fluoride. Lily fertilisers are chosen to be low in fluorine for the same reason. A coir and husk-chip mix sidesteps the perlite problem, which is one reason forcers ask about it.
Lilies are also more salt-sensitive than tulips. Dutch water-reuse rules allow drain water up to 5 mmol sodium per litre for tulips, but the limit for lily and iris was lowered to 3 mmol/l after flower quality dropped at 5. That's the number to hold a coir supplier to. Salty coir has to be flushed with low-sodium water before bulbs go in, and on a weekly planting schedule nobody has time for that. Whether bulb forcers need washed or calcium-buffered coir is covered in buffered vs unbuffered coco peat.
Watering and drainage in crates
Overwatering kills bulbs through oxygen deficiency, and Pythium follows. Underwatering dries the top layer where the stem roots are forming. The working rule is that medium just under the bulb should form a compact ball in the hand. Water early in the day with cold water. Once the canopy closes and humidity is high, apply water at the substrate surface rather than over the leaves to keep Botrytis off, and hold greenhouse humidity below 80%.
A crate of fine, wet coir can go anaerobic in the middle of a pallet stack. The fix is physical: a coarser grade or a coir and husk-chip blend, and a lined but not sealed crate base. Tulips in substrate need little water early in the greenhouse and almost daily water in the last week.
Disease and hygiene
The pathogens are the same whatever the medium: Pythium and Phytophthora root rots, Fusarium basal rot, Rhizoctonia, Penicillium in store and Botrytis (tulip fire) in the house. The difference is where the inoculum comes from.
- Steam greenhouse soil to 70–80 °C for 30 minutes before replanting, or solarise under plastic for 4–6 weeks in summer. Coir arrives clean rather than sterile, which is the point of using it in crates instead. What that means in practice is in is coco coir sterile.
- Wash and disinfect crates between batches. Rhizoctonia and Pythium carry over on the plastic. Water-forcing trays get hydrogen peroxide for the same reason.
- Disinfect bulbs against Fusarium, Botrytis and Pythium before planting, peel the brown tunic off tulips so the root plate isn't scorched, and don't bruise bulbs. Damaged bulbs are where Pythium starts.
- Rogue out any bulb that hasn't emerged when the crop is 5–10 cm tall. It's rotting and gassing its neighbours.
- Tools: 10% household bleach or 70% alcohol between lots.
- Keep water forcing and substrate forcing in separate houses.
A very dense root mat is more prone to Trichoderma than an open one, another argument for a coarser grade than you'd use for seedlings.
Reusing the substrate
Dutch tulip forcers used to compost and reuse their soil because peat is imported and expensive, and they paid for it in fungicide. The advice from forcers who don't have to is blunt: spent crate contents, bulbs, roots and all, make fine garden compost and should not go back into bulb forcing. Each batch brings its own Fusarium and Pythium, and a 14-week crate cycle gives them time to build. Coir's structure would survive two or three crops, so the limit is hygiene, not the fibre. If you reuse it, follow reusing coco coir and put it under a non-bulb crop.
What forcers specify when they buy coir
| Spec | What bulb forcers ask for | Why |
|---|---|---|
| EC | Low, washed. Ask for the test method (1:1.5 or 1:5 extract) | Tulips tolerate salt, lilies and iris don't. Reuse limit 3 mmol Na/l for lily |
| Sodium and chloride | Low, with figures | Calcium uptake falls as sodium rises, and that's what causes leaf topple in tulips |
| pH | 5.5–6.5 out of the bag | Lands in range for Orientals and tulips, easy to lime for Asiatics |
| Grade | Medium to coarse, or a coir and chip blend. Fines for the base layer only | Air for stem roots, drainage in stacked crates |
| Buffering | Usually not required | One short crop, calcium nitrate in the feed anyway |
| Moisture and form | Compressed blocks or briquettes that expand predictably | Crates are filled by machine at 60 per pallet |
| Cleanliness | Free of weed seed and soil, pasteurised if the buyer's protocol demands it | Replaces steamed soil |
CVM Fiber and Industries makes coco peat in Kanyakumari, Tamil Nadu, India, from husk sourced across several districts. It's washed with water to reduce EC, with no calcium nitrate or other chemicals added, so it's unbuffered. Blocks, briquettes, husk chips and custom blends can be matched to a crate protocol. If you want to trial coir against your current mix, tell us the crop, crate and cold schedule and we'll suggest a grade.
FAQ
Can you force tulips in coco coir instead of peat?
Yes. Tulips are forced in any clean, well-drained soilless mix, and washed coir at pH 5.5–6.5 meets the published targets. Use about 7.5 cm under the bulb, cover 5–8 cm with a coarser grade on top, and keep the crate moist through the whole cold period. Water forcing is now the bigger share in the Netherlands, but substrate-forced tulips still give longer stems and brighter colour.
How many tulip bulbs fit in a forcing crate?
Sixty bulbs of 12/+ size in ten rows of six is the standard layout, and 60–70 is the usual range. Smaller 11/12 bulbs can go to 100–105 per crate. Place them almost touching, like eggs in a carton, and keep the tips visible after watering.
What temperature should the rooting room be?
Start at 9 °C, or 5 °C for pre-cooled bulbs, and drop 2 °C at a time to 0 °C once roots have formed. Never go below −2 °C. US guides give 4–9 °C for two to three weeks of rooting, then 1 °C for the rest of a 14–18 week cold period. Humidity around the crates should be 90–95%.
What EC and pH do forced bulbs need?
Tulips: extract EC of 1–1.5 mS/cm and pH 5.5–6.8 depending on the guide. Water-forced tulips are filled at EC 1.7–2.0 with calcium nitrate and run at 1.5. Lilies: pH 6–7 for Asiatics and longiflorum, 5.5–6.5 for Orientals, and 6.8–7.2 where fluoride scorch is a risk. Lilies are more salt-sensitive than tulips, with a sodium reuse limit of 3 mmol/l against 5 for tulip.
Why do lily growers avoid perlite?
Perlite and superphosphate both carry fluoride, and some lily cultivars develop leaf scorch from it. The advice for sensitive cultivars is to keep pH at 6.8–7.2, keep calcium up, and leave both out of the mix. Coir blended with husk chips gives the same aeration without the fluoride source.
Can the coir be reused for the next batch of bulbs?
Forcers advise against it. Each batch brings its own Fusarium and Pythium, and a 12–18 week crate cycle gives them time to build up. Dutch growers who reused composted soil relied on heavy fungicide use to get away with it. Compost the spent crate contents or use them on a non-bulb crop, and start each bulb batch in fresh medium and disinfected crates.
Is forcing in substrate slower than on water?
No. Both take about 3 to 3.5 weeks in the greenhouse at the right temperature. Water-forced tulips are run 1–2 °C cooler, at about 17 °C against 18–19 °C, and if you give them the same temperature they finish two days earlier but with lower quality. In hyacinths, water forcing was 1 to 5 days faster but substrate gave longer stems.