The short answer: aubergine grows well in washed coco coir, in slabs, bags or Dutch buckets. Train each plant to 2–3 stems (up to 4 under a low roof) for 5–8 stems/m², give it at least 3.5 L of substrate per plant, and keep the feed EC lower than most charts suggest. In the trials below, yield peaked between EC 1.8 and 2.5, not at 3.0 and above. The crop is less fussy in the root zone than tomato. Most of the yield you lose comes from poor fruit set, either from weak flowers in low light or from heat.
Key facts
- Stem density: 5–8 stems/m², commonly 3 stems per plant at about 1.7 plants/m² (5.1 stems/m²).
- 3.5 L of coir-perlite per two-stemmed plant gave statistically the same yield as 7 L.
- In a glasshouse trial at EC 1.8, 2.8 and 3.8, yield fell as EC rose. Fruit was heavier and longer at 1.8.
- Bumblebee pollination gave about 25% more yield than mechanical vibration, with fruit 14% heavier.
- Well-run heated glasshouses report 50 to 65 kg/m² over a long season.
Why aubergine suits coir
Aubergine is a long, vigorous crop. Planted around December in northern glasshouses, it is picked from February to late October, often three times a week. That is ten months of roots in one slab, so you want a substrate that keeps its structure and air space through the season. Coir does that.
The bigger risk with aubergine is a root zone that stays too wet. Growers who run the crop on stone wool describe the same thing: in spring and autumn, a waterlogged slab turns the crop yellow, throws it off balance and slows production. A coir slab with a good share of coarse material drains freely and keeps the top layer drier and better aerated, which is where aubergine roots like to be. If you're converting from tomatoes or peppers, the slab or bag you already use is a reasonable starting point.
Plant density and stem training
| Layout | Stems per plant | Plants/m² | Stems/m² |
|---|---|---|---|
| Typical glasshouse | 3 | 1.67 | 5.1 |
| Low winter light (lit crop) | 2–3, side stems added in spring | lower | 3.4 rising to 5.1 |
| Four-stem plants, 30 cm apart, rows 90 cm | 4 | about 1.8 | 7.2 |
| General range | 2–4 | varies | 5–8 |
The first strong side shoot sits just below the first flower cluster. On a two-stem plant, keep that shoot as the second stem. For three or four stems, keep the next strongest shoots below it. Use four stems in a short house, because the plants take longer to reach the wire. Two stems give more vigour per stem. With poor light or ventilation, go to the low end of the range.
Density should follow light. In a lit winter crop at 5.1 stems/m², too little assimilate reached the fruit, set was patchy, and fruit took up to 27 days to size. Modelling for the same crop suggested that starting at 3.4 stems/m² and taking extra side stems in February–March, as light increases, would add about 4 kg/m² between November and March.
Side shoots and leaves
Don't strip side shoots the way you would on tomato. Let each one grow, then cut it just above its first flower or two. Keeping no more than two fruits per side shoot holds the plant in balance. Three or four per shoot overloads it. Remove leaves below the lowest developing fruit, cut flush to the stem, and keep doing so as you harvest up the plant. Wind or clip the stems to the string every 10–14 days.
Substrate volume: slabs, bags and buckets
Aubergine is forgiving about root volume. Two-stemmed plants in a 50:50 coir-perlite mix produced 1,809 g per plant in 7 L pots and 1,492 g in 3.5 L pots, and the difference wasn't statistically significant. Neither was the difference in water-use efficiency (15.7 vs 13.0 kg of fruit per m³ of water). So 3.5 L per plant is a workable floor. More volume gives you a bigger water buffer on hot days.
| System | What to check | Coir per plant |
|---|---|---|
| Slab, 1 m | Slab volume divided by plants per slab at your spacing | 3.5 L or more |
| Grow bag | Same sum, bag volume per plant | 3.5 L or more |
| Dutch bucket | Bucket volume per plant, with a coarse blend | 3.5 L or more |
| Pot (trial setup) | One two-stem plant per pot | 3.5 L gave the same yield as 7 L |
Commercial aubergine slabs have moved from 7.5 cm to 10 cm high, which gives more buffer and a drier top layer at the same time. If you run buckets, Dutch bucket hydroponics with coco coir covers media and layout.
EC and pH by stage
The trials point the same way: aubergine doesn't need a strong feed.
| Stage | Feed EC (mS/cm) | pH | Notes |
|---|---|---|---|
| Propagation | 2.5–3.5 | 5.5 | Keep plants dark green and compact |
| First week after planting | Low end of your production range | 5.0–6.2 | 24°C day and night to get roots into the slab |
| Fruit set and full load | 1.8–2.5 | 5.0–6.2 | Raise only if fruit quality or plant balance calls for it |
In coir dust bags fed at EC 1.0 to 3.5, fruit dry matter peaked at about 1.9 and shoot dry matter at about 2.4. In a glasshouse trial at EC 1.8, 2.8 and 3.8, both cultivars yielded best at 1.8, with heavier, longer and wider fruit and lower running costs. Drip water pH between 5.0 and 6.2 is the usual working window for substrate crops.
Watch calcium and magnesium. In the coir dust trial, leaf calcium and fruit calcium and magnesium fell below adequate levels, and raising them in the solution was the fix. Washed, unbuffered coir takes calcium and magnesium out of the first feeds, so condition the slabs before planting. The nutrient solution guide for coco coir sets out the recipe changes.
Irrigation and drain
Run aubergine on the slightly dry side. Start with small shots once the plant is transpiring, let the slab dry back overnight, and adjust drain by watching the root-zone EC rather than following a fixed percentage. If the slab stays heavy into the afternoon in spring or autumn, cut the shot count before you see yellowing. Shot sizes, start and stop times and drain targets are covered in irrigating coco coir slabs.
Pollination and fruit set
Aubergine is self-compatible, and it will set some fruit without help. Assisted pollination still pays. In unheated greenhouses, bumblebees gave about 25% more yield than mechanical vibration. Fruit was 14% heavier and 7% longer, with four times as many seeds. Put the hives in as soon as the first flowers open. In one lit trial, hives arrived three days after first flowering, and part of the first truss was lost.
Flower quality matters as much as the bees. Aubergine flowers come with long, medium or short styles. Long-style flowers set well, while short-style flowers rarely set. Short styles appear when the plant is short of assimilates. On one December date in a low-light winter crop, 62% of open flowers had short styles. Lower stem density, a bigger day-night temperature difference and a lighter fruit load all help.
| Climate factor | Range |
|---|---|
| Stable fruit set, mean daily temperature | 16–25°C |
| Day, fruit setting | about 22°C |
| Day and night, full fruit load | 20–22°C day, 17–19°C night |
| Night minimum | about 18°C |
| Pollen viability fails | below 15°C during flowering |
| Set falls off | above 35°C |
In hot climates, heat is the limit. Most cultivars set less fruit above 35°C, mainly because pollen loses viability. Shade, ventilation and fogging to keep peaks down will do more for set than any change to the feed.
Fruit load
The Dutch trial aimed for about 15 fruits per m² carried on the plant. Fewer means the plant goes vegetative, with thick heads and low flowers. More means stalled fruit and set gaps. Read the head. When the head gets too thick, let fruit hang longer and grow heavier to add load. Fruit on side stems can be picked lighter than fruit on the main stems.
Disorders linked to the root zone
Blossom-end rot. A tan, water-soaked patch at the blossom end that turns dark and leathery. It is a calcium supply problem at the fruit, not a lack of calcium in the feed. Swings in moisture, high salinity, heat and high ammonium all make it worse, and plants in containers are more prone than plants in soil. Steady irrigation, a moderate EC and enough calcium early in the crop do most of the work. Foliar calcium is of disputed value because very little reaches the fruit.
Fruit cracking. Less documented in aubergine than in tomato. Where it appears, look first at uneven water supply and large swings in slab moisture.
Poor set in heat. See the climate table. A higher EC adds osmotic stress on top of heat, which is one more reason to keep the summer feed at the low end.
Pests that follow plant stress
Aubergine is a favourite host of both whitefly and two-spotted spider mite. Mites build up fastest at 20–30°C with humidity around 30–50%, and their bronzing damage is easily mistaken for drought stress. Plants that run dry between shots or sit in hot, dry corners near heating pipes are where outbreaks start, so scout those spots first. Even irrigation and enough humidity are part of mite control.
Yields: trials and commercial figures
| Setting | Yield |
|---|---|
| Small-pot coir-perlite trial, 2 stems | 1.5–1.8 kg per plant |
| Glasshouse EC trial, two cultivars | 0.81–1.14 kg/m² per week |
| Unheated or cold houses, peat substrates | 2.6–7.9 kg/m² |
| Lit winter crop, November to February | 11–14 kg/m² |
| Heated glasshouse, full season | 50–65 kg/m² |
The range is wide because season length, heating, light and cultivar dominate. The 60+ kg/m² figures come from grafted plants under diffuse glass, picked through most of the year. A short unheated season won't reach them on any substrate.
What to specify when buying substrate for aubergine
- Format and height. 1 m open-top slabs or grow bags, 10 cm high, or loose coir for buckets.
- Litres per plant. At least 3.5 L, and more in hot, high-light climates.
- Pith-to-chip ratio. A coarser blend keeps the top layer drier and better aerated, which suits the crop's dislike of wet roots.
- Washing and buffering. Ask whether the coir is washed and whether it is buffered, and plan your calcium and magnesium conditioning to match. Our buffered vs unbuffered coco peat article explains the difference.
- Film and holes. Plant holes to match your spacing, and drain slits on the low side of the gutter.
CVM Fiber and Industries makes open-top slabs and grow bags in Kanyakumari, Tamil Nadu, India. Our coco peat is washed with water to reduce EC, with no calcium nitrate or other chemicals, and it is not buffered. If you're planning an aubergine crop and want to talk through slab size and blend, contact us.
FAQ
How many stems should a greenhouse aubergine have?
Two to three stems is standard, with four used in shorter houses. Aim for 5–8 stems per square metre overall. In low winter light, start nearer 3.4 stems per square metre and add side stems as light increases in spring.
What EC should I feed aubergine in coco coir?
Most trials found the best yields between EC 1.8 and 2.5. In one glasshouse comparison, EC 1.8 beat 2.8 and 3.8 on yield and fruit size. Propagation feeds run higher, around 2.5–3.5, with pH near 5.5.
How much coir does each aubergine plant need?
About 3.5 litres per plant is a workable minimum. In a coir-perlite trial, 3.5 L and 7 L pots gave yields that weren't statistically different. More volume gives a bigger water buffer in hot weather.
Do aubergines need bumblebees in a greenhouse?
No, they are self-compatible and will set some fruit without help. Bumblebees still give more yield than vibration, about a quarter more, with heavier fruit. Introduce the hives when the first flowers open.
Why are my aubergine flowers dropping without setting fruit?
Usually short-style flowers from a plant short of assimilates, or pollen damaged by temperatures below 15°C or above 35°C. Lower stem density, a lighter fruit load and keeping temperature peaks down all help.
Can I grow aubergine in Dutch buckets with coir?
Yes. Keep at least 3.5 litres of coir per plant, use a coarse blend, and let the medium dry back between irrigations. Aubergine dislikes a constantly wet root zone more than it dislikes a small one.
What yield can I expect from aubergine on coir slabs?
It depends far more on season length, heating and light than on substrate. Heated glasshouses running a ten-month crop report 50–65 kg per square metre. Shorter or unheated crops produce a fraction of that.
Does aubergine get blossom-end rot in coir?
It can, especially in containers. The causes are uneven moisture, high salinity, heat and too much ammonium nitrogen. Keep irrigation steady and EC moderate, and make sure calcium is supplied from the start.