The short answer: roses and gerbera grow well on coco coir, and most of the large cut-flower farms that have left the soil in Kenya, Colombia and the Netherlands now use coir or a coir blend. Roses go on long slabs or bags at about 2.5 to 4 litres of substrate per plant, 6 to 7.5 plants per m², feed EC around 1.0 to 1.6 mS/cm and drain held under about 2.8 to 3.0. Gerbera has moved almost entirely to individual pots, takes a higher EC (up to 2.2 to 3.0 in a soilless system) and is far more sensitive to wet roots than roses. Chrysanthemum is still mostly a soil crop. The details, and the mistakes that cost growers money, are below.
Why cut-flower farms went soilless, and why coir
Rose and gerbera crops stay in place for years, so soil-borne disease, nematodes and salt pile up in the beds with no rotation to break the cycle. Colombian growers moved roses onto substrate mainly to escape soil pests and root disease. Kenyan farms around Naivasha did the same, and water pushed them further: a cocopeat system with drain re-use on one Naivasha farm used 1,197 L/m² (58%) less water than its soil beds.
Coir won most of that market because it holds a lot of water and still drains, has real cation exchange capacity (100 to 150 meq per 100 g is quoted for coconut fibre), ships compressed and composts when the crop comes out. In a two-year recirculating trial, cut roses on coir gave 15.6% more marketable stems and 18% more fresh weight than granulated rockwool in year one, and the same in year two. If you're still weighing coir against stone wool, read coco coir vs rockwool first.
Roses on coir slabs and bags
Volume per plant and density
The standard Dutch rose system is a 100 cm slab, 7.5 cm high and 19.5 or 23.5 cm wide, with 6 to 8 plants per slab at 6.0 to 7.5 plants per m². That gives 18 to 24 L of substrate per m², or roughly 2.5 to 4 L per plant. Those numbers come from stone wool, but coir slabs for roses follow the same footprint because the gutters and drippers are already built for it.
Pots and bags carry more. A Colombian trial used 8 L pots with two plants each (4 L per plant) on suspended beds at about 7 plants per linear metre. A 10 cm high slab is now sold for growers who want the substrate to outlast the usual cycle. The same logic applies to coir: taller and coarser keeps its air longer, at the cost of a wetter bottom layer and slower EC response.
Chips vs pith for roses
A rose slab has to hold its structure for five years or more. Dutch rose nurseries replant every 4 to 6 years, and some growers aim for 9 or 10. Pure coco pith settles and loses air over that time, so rose slabs lean coarse.
- Pure pith: holds the most water and roots fastest. Kenyan growers describe young plants rooting "very evenly" in it. On its own it goes vegetative and compacts over a long crop.
- Pith and chips blends: the usual commercial answer. Multi-year grow bags run from a pith-over-chips layered design to 70% chips.
- Coir with perlite or pumice: a 1:1 perlite and coir dust mix gave 17.7 stems per plant and 65 cm stems in a two-year Sicilian trial, the best of the media tested, while using 0.62 L of water per plant per day against 0.78 L on perlite alone. Kenyan farms blend coco peat with pumice for the same reason.
A sensible starting specification for a rose slab is 50 to 70% pith with 30 to 50% husk chips by volume, washed to a low EC. The coconut husk chips guide covers chip grades and how they behave.
EC and pH for roses
Roses are salt-sensitive, and the yield penalty for high EC shows up a few flushes later rather than at once.
- Feed EC: a widely used Japanese standard rose solution runs 1.0 mS/cm in high summer, 1.4 in spring and autumn and 1.6 in winter. In a cocopeat and perlite trial on that standard, feeding at 0.7 times strength gave heavier flowers, thicker stems and more 91 cm plus stems. Feeding at 1.3 times strength cut yield from the fourth flush onward.
- Slab or drain EC: keep it under about 2.8 to 3.0 mS/cm. Measured drain EC in a recirculating coir rose system ran from 2.6 up to 5.9 mS/cm in summer, against 2.2 to 3.9 on pumice. Coir holds salt harder than inert media do.
- pH: drain pH around 6.0 is typical. Coir tends to pull pH down over time, so expect to use less acid than on stone wool.
Check feed and drain weekly at minimum. The crop-wide method is in coco coir pH and EC management and isn't repeated here.
Irrigation and drain for roses
Rose crops on coir drink 0.6 to 1.0 L per plant per day in a temperate greenhouse, in many small shots. One recirculating system gave 800 ml per plant per day in 8 equal doses. Published drain fractions run from 25 to 35% in Italy to 30 to 50% in Colombia. More drain keeps slab EC down but costs water and fertiliser, which is why most farms collect and re-use it. Switching from timer to moisture-sensor control in coir cut nutrient solution use by 59% with only a small drop in yield.
Pre-saturate new slabs with full nutrient solution, not plain water. Coir arrives holding potassium and sodium on its exchange sites and will swap them for the calcium in your first feeds. How much depends on whether you bought buffered or washed coir. Buffered vs unbuffered coco peat explains the difference.
Gerbera in coir pots
Pots, not slabs
Gerbera has switched almost completely from slabs to individual pots. One plant per pot means you can pull a diseased plant without disturbing its neighbours. Protocols quote pots of 20 to 25 cm diameter and up to 40 cm tall. Trials have used 3 to 12 L per plant, and over a two-year crop in 5 L containers coir has given the highest production of the media tested. Pots sit off the ground, on cables or benches, with drain collected underneath. Net density is 7 to 9 plants per m², about 6 per gross m².
Substrate for gerbera
Gerbera wants an airier substrate than roses. One breeder's protocol asks for coco peat with 50% long fibres, a different animal from fine pith. In coco peat and perlite trials, mixes between 50:50 and 75:25 coco to perlite gave the best growth and the most flowers. Avoid fine, dusty grades for this crop.
One caveat for anyone buying unbuffered coir: in gerbera, untreated coir has produced significantly fewer flowers than pre-treated coir or a pine bark and coir blend. Washing brings EC down but leaves potassium and sodium on the exchange sites, so either buy buffered coir for gerbera or pre-soak with a calcium-rich feed and watch calcium and magnesium in the drain for the first month.
EC, pH and irrigation for gerbera
- Feed EC: 1.5 to 2.0 mS/cm is common in trials. Protocols allow up to 2.2 to 3.0 in soilless systems, against 1.1 to 1.6 in soil. Indian polyhouse growers on coco peat typically run 1.2 to 1.5.
- Drain EC: no more than about 20% above feed. If feed is 2.0, drain over 2.4 means salt is accumulating.
- pH: feed at 5.5 to 6.0. Substrate pH of 5.2 to 6.3 is the quoted range. Gerbera pushes substrate pH up over time and coir pulls it down, so the two roughly cancel.
- Irrigation: gerbera is more sensitive to over-watering than to drought. Protocols call for pulses of about 200 ml per plant, 6 to 8 pulses a day in a free-draining pot, and no irrigation in the last four hours before dark so roots dry a little overnight. Daily use is roughly 500 to 700 ml per plant in India and 800 to 1,200 ml in a southern European greenhouse.
Plant with the crown at or just above the substrate surface. Burying it is the quickest route to crown rot.
Chrysanthemum: mostly still in soil
Cut chrysanthemum is a short crop and in the Netherlands it's still almost entirely soil-grown. Soilless systems have been researched for years to cut fertiliser and pesticide emissions, but the ones that worked best were deep-flow water beds and aeroponics rather than substrate. In a Dutch substrate cassette trial, peat and perlite outgrew coir and sand, and the researchers could not explain the gap by oxygen supply.
Where coir earns its place is propagation and blends. Cuttings root very well in coco peat, which is why many propagation plugs are coir-based. In hydroponic trials with 'Puma', 75:25 coco peat to perlite gave the best vegetative growth and 50:50 the most flowers. A workable EC programme from the Dutch work: start around 1.2 mS/cm and raise to about 2.8 eight days into short days, which shortened stems enough to skip growth regulators.
Indicative targets by crop
| Roses | Gerbera | Chrysanthemum (soilless trials) | |
|---|---|---|---|
| Container | 100 cm slab or bag, 7.5–10 cm high | Individual pot, 20–25 cm dia | Bed, cassette or pot |
| Substrate per plant | 2.5–4 L | 3–12 L (5 L in a two-year trial) | Varies |
| Density | 6–7.5 plants/m² | 7–9 net, ~6 gross plants/m² | Soil norms apply |
| Coir grade | 50–70% pith, 30–50% chips, or 1:1 with perlite | Coarse pith with ~50% long fibre, or 50–75% coir with perlite | 50–75% coco peat with perlite |
| Feed EC (mS/cm) | 1.0–1.6, seasonal | 1.5–2.0, up to 2.2–3.0 max | 1.2 start, up to 2.8 in short days |
| Drain EC | Under ~2.8–3.0 | Not more than ~20% above feed | Close to feed |
| Feed pH | 5.5–6.0, drain ~6.0 | 5.5–6.0, substrate 5.2–6.3 | 5.5–6.0 |
| Daily water | 0.6–1.0 L/plant | 0.5–1.2 L/plant by season | By radiation |
| Drain fraction | 25–50% | Low: ~200 ml pulses, 6–8/day | 15–30% |
| Crop on same substrate | 4–6 years, some to 9–10 | ~2 years | One crop |
These are starting points from published trials and grower protocols in several countries. Your cultivar, water quality and climate will move them.
Slab life and replacement
Rose growers replant every 4 to 6 years and want the substrate to last the whole crop. There's no published lifespan figure for coir rose slabs, so growers watch three things. Air content: pith settles, and a slab that was 7.5 cm and is now 5.5 cm has lost a third of its air, which is when root disease starts and stem weight falls. EC drift: if drain EC keeps rising while feed and drain fraction stay the same, the slab is loading up, so flush before you blame the plants. Root mass: a five-year slab is more root than coir by the end, which is fine until drainage slows and the bottom stays saturated. Gerbera pots are usually renewed with the plants at about two years.
Common problems
Salt build-up. The number one issue in coir rose and gerbera crops. Coir's exchange capacity means sodium and potassium accumulate in the slab rather than leaving in the drain. Signs: drain EC climbing above target, leaf margin scorch, smaller flowers two flushes later. Fix: raise drain fraction for a week, flush with a lower-EC solution, and check the sodium in your source water. In Colombian recirculating rose systems, drain EC and pH crept up over the whole cycle even while staying under the damage threshold.
Root disease in wet coir. Phytophthora cryptogea in gerbera and Pythium in both crops thrive in saturated substrate. In a recirculating gerbera trial, the wettest, lowest-EC treatment killed 73.6% of plants and the driest, highest-EC treatment 4.7%, with no fungicide. Let pots dry a little between pulses, stop irrigating four hours before dark, and keep pots off the floor. Over-fine coir makes this worse.
Vegetative, soft stems. Pure fine pith plus low EC is the recipe. Add chips, raise EC a little and cut drain.
Dry pockets in new slabs. Fully dried coir is slow to rewet. Saturate slabs completely before cutting drainage slits.
What to specify when you buy
Describe the substrate in terms a manufacturer can control, and get the numbers in writing before the container ships.
- Format and dimensions. Slab or bag length, expanded height (7.5 or 10 cm) and width to fit your gutter, with pre-cut planting holes if wanted. For gerbera, fill volume per pot. Formats are explained in coco coir grow bags explained.
- Pith to chips ratio by volume, and chip size. Say 60:40 pith to 6–12 mm chips rather than "medium grade". For gerbera, specify long fibre content.
- EC after washing, and the test method, so you can compare quotes.
- Buffered or washed only. Washed-only coir costs less and suits rose growers who pre-saturate with a calcium feed. Gerbera growers, and anyone with sodium in their water, should think hard about buffered.
- Consistency between lots. A multi-year rose crop can't absorb a change in chip ratio halfway through replanting a greenhouse.
CVM Fiber and Industries in Kanyakumari, Tamil Nadu, India makes open-top slabs, grow bags, husk chips and custom pith-and-chips blends for these systems. Our coco peat is washed with water to bring EC down, with no calcium nitrate or other chemicals, and it is not buffered. If you're running roses or gerbera and want a blend matched to your gutter width, chip ratio and EC target, send us your specification and we'll quote against it.
FAQ
Can roses really be grown in coco coir long term?
Yes. Dutch rose nurseries run crops of 4 to 6 years on substrate, and coir is one of the two mainstream choices alongside stone wool. In a two-year recirculating trial coir gave more marketable stems than granulated rockwool in the first year and equal yield in the second. The key is a chips and pith blend that keeps its air content for the life of the crop.
How many litres of coir does a rose plant need?
About 2.5 to 4 litres. The Dutch standard is 18 to 24 litres of substrate per square metre at 6 to 7.5 plants per square metre, on 100 cm slabs 7.5 cm high. Pot systems in Colombia use 8 litre pots with two plants each. More volume gives more buffer against irrigation errors but slows EC response.
What EC should I run for roses on coir?
Feed around 1.0 to 1.6 mS/cm depending on season, lower in summer and higher in winter, and keep slab or drain EC under about 2.8 to 3.0. Roses are salt-sensitive and the yield penalty for high EC shows up several flushes later. Feeding at the low end gave heavier flowers and thicker stems in a cocopeat and perlite trial.
What EC and pH does gerbera want in coco peat?
Feed at pH 5.5 to 6.0 and EC 1.5 to 2.0 mS/cm, with a ceiling of about 2.2 to 3.0 in a soilless system. Drain EC should be no more than about 20% above the feed. Substrate pH between 5.2 and 6.3 is the quoted range. Indian polyhouse growers commonly run 1.2 to 1.5 mS/cm.
Why do gerbera growers use pots instead of slabs?
Gerbera cultivation has moved almost entirely from slabs to individual pots of 20 to 25 cm diameter. One plant per pot lets you remove a plant with Phytophthora or Fusarium without disturbing the rest, and replace plants piecemeal. Pots raised on benches or cables also drain freely, which matters because gerbera is more sensitive to over-watering than to drought.
Should I use pure coco peat or a chips blend for cut flowers?
A blend. Pure fine pith roots quickly but settles, holds too much water and gives soft vegetative growth over a multi-year rose crop. Rose slabs commonly carry 30 to 50% husk chips or a 1:1 coir and perlite mix. Gerbera protocols ask for coco peat with about 50% long fibre. Save pure fine pith for propagation.
How much drain should I aim for with roses on coir?
Published rose systems run 25 to 50% drain, with 30% a common working figure. More drain keeps slab EC down but wastes water and fertiliser unless you recirculate. A Kenyan farm that caught and re-used drain from a cocopeat system used 58% less water than its soil beds, and sensor-controlled irrigation in coir cut nutrient solution use by 59%.
Is coco coir good for chrysanthemum?
For rooting cuttings, very good, and most propagation plugs are coir-based. For the production crop, cut chrysanthemum is still mostly soil-grown, and in Dutch soilless trials a peat and perlite mix outperformed coir. Where coir and perlite blends have been used for chrysanthemum, 50:50 to 75:25 coco peat to perlite gave the best results.