The mistake that costs a soilless greenhouse its first harvest is made before planting: laying the substrate bags flat on bare soil, with no slope and no drainage collection. The substrate waterlogs from the bottom up, roots suffocate in the last few centimetres, and the nutrient solution runs off into the ground instead of being measured. The equipment to put in place before the first plant comes down to this: a support with a slope, bags or troughs holding the right volume per plant, one dripper per plant, a drainage collection point, and an EC meter paired with a pH meter.
The equipment to install before the first plant
The order of assembly matters. Each piece determines how the next one is set, and going back once the plants are in place costs a season.
- The support: a bench, a raised bed or a compacted sand base, with a steady slope along its length. The University of Florida greenhouse vegetable production handbook uses a slope of about 1 inch per 100 inches of length on solution flow channels, which is 1 percent. Treat that as a floor: below it, drainage stalls.
- The container: growing bag, trough or gutter. The troughs described in the same handbook are 15 to 20 cm deep and 45 to 75 cm wide. Lay-flat bags hold about half a cubic foot of substrate, in 4 mil polyethylene film, and take up to three tomato plants or two cucumber plants.
- The substrate, in a quantity worked out per plant rather than per bag.
- The irrigation line and the drippers, one per plant, fitted before the blocks go in.
- Drainage collection: a gutter, a return pipe and a graduated container at the low point of each row.
- The measuring instruments: EC meter and pH meter, calibrated before the first watering.
Choosing the substrate material is a separate decision, and it comes before you order the bags: the density, water retention and working life of coir, rice hulls and sand are not alike. We covered it in our comparison of substrates for a soilless crop under greenhouse.
Substrate volume per plant
This is the figure that decides everything else, because it fixes the water reserve available between two waterings. Two references, two orders of magnitude, and the difference can be explained.
The soilless growing training sheet published by the Direction du Développement Rural of province Sud of New Caledonia uses about 5 litres of substrate per plant for fruiting vegetables, at 3 plants per coir bag, and 3 to 4 litres per plant for leafy vegetables, at 4 or 5 plants per bag. Eggplant, sweet pepper and tomato fall in the first group.
The University of Florida handbook is more generous: one third to one half of a cubic foot of mix per plant, which is roughly 9 to 14 litres. The two figures complement each other. A smaller volume forces more frequent watering and tighter drainage monitoring, and it is less forgiving of a pump outage. Under a tunnel fed from a tank on solar pumping, where watering frequency depends on sunshine, the larger volume buys you margin. If you are starting out, aim for the top of the province Sud range and above.
Check this volume once the bags are filled, not on the order form: fill one bag, weigh it, count the plants it will carry, and divide.
One dripper per plant, and the flow rate that goes with it
The rule is simple and it allows no exception in soilless growing: one dripper per plant. A bag with three plants therefore gets three drippers, which the province Sud sheet confirms, and its worked example uses a flow rate of 2 litres per hour per dripper.
Why this rule is stricter than in open ground: there is no soil to redistribute water sideways. A plant without its dripper gets nothing, and its neighbour gets twice as much. In open ground the same fault shows up as uneven growth; in soilless growing, as a lost plant.
At 2 litres per hour and 5 litres of substrate, a ten minute watering delivers about 0.33 litre per plant. Do the arithmetic for your own flow rate before you programme a single cycle, and check the real flow by catching one dripper’s output in a graduated container for one minute, on the first and the last dripper of the row. A gap between the two points to a pressure loss along the line, and it is corrected before planting. The usual causes of clogging and flow drift are the same as in open field market gardening, and we listed them in the mistakes that make small drip schemes fail.
Collecting 30 percent drainage, and measuring it
In soilless growing, drainage serves as a measuring instrument as much as an outlet. The province Sud sheet sets the optimum at 30 percent of the volume applied. In other words, of 10 litres delivered to a row, 3 should come back at the low point.
That figure reads both ways. Drainage well below 30 percent means the substrate is accumulating salts and the root zone is drying out between applications. Drainage well above it wastes water and fertiliser, and leaches the nutrient reserve before the plant uses it.
Measure daily, at the same time, with a graduated bucket under the return of one reference row. Measure the EC of the drainage too, not only its volume: it is the comparison between the solution going in and the drainage coming out that tells you what is happening inside the bag.
EC and pH: the two readings that steer the crop
Electrical conductivity tells you the salt concentration of the solution, pH tells you how available it is to the plant. The province Sud figures for fruiting vegetables: an EC of 2.5 to 3 in the hot season, 2.8 to 3.5 in the cool season. For leafy vegetables, 1 to 1.5 in the hot season and 1.2 to 2 in the cool season. The optimum solution pH sits between 5.8 and 6.2.
The Center for Crop Diversification sheet from the University of Kentucky, on selecting growing media for soilless systems, gives a slightly wider band for hydroponic production in general: an optimal pH between 5.5 and 6.5.
On the substrate side, the University of Florida handbook sets an alert threshold: above 3.0 mmhos measured in the medium, excess salts are established and a flush with plain water, no fertiliser, is needed. For starter tray systems, the same handbook asks that the soluble salt concentration of the medium not vary by more than 1.0 mmho from that of the applied solution. Both values mark the point at which you must act, not a target to reach.
One detail that prevents a false diagnosis: an EC rising in the drainage while the incoming solution has not changed does not signal a fertiliser problem, it signals insufficient drainage. Check the volume before you touch the recipe.
How many waterings a day in a hot climate
The province Sud sheet uses 6 waterings a day in the hot season for fruiting vegetables and 5 in the cool season. For leafy vegetables, 4 and 3. These frequencies go with a volume of about 5 litres per plant: with a larger container, you water less often and for longer.
Under a tunnel in West and Central Africa, two adjustments are needed. The first concerns the time of the last application: night ventilation and air humidity decide the state of the foliage in the morning, and a late watering keeps condensation going. That is the subject of our article on condensation under a tunnel greenhouse. The second concerns a power or pumping outage: a soilless crop with no buffer water reserve will not last a day, and the tank is sized accordingly.
For the detailed management of a cash crop grown soilless, with its nutrient solution and pruning calendar, see our sheet on soilless tomato under greenhouse.
The costliest installation mistakes
| Mistake | What you see | Correction |
|---|---|---|
| Bags laid flat with no slope | Saturated bag base, brown roots at the bottom | Rest them on a support with at least 1 percent slope |
| No drainage collection | No way to tell whether you are over or under watering | Gutter and graduated container on one reference row |
| Substrate volume too small | Midday wilting despite the waterings | Increase the volume per plant or cut the number of plants per bag |
| One dripper for two plants | Every second plant lags, then dies | One dripper per plant, no exception |
| Drainage slits cut after filling | Washed out substrate, blocked slits | Cut them before filling, low on the side and not underneath the bag |
| Uncalibrated instruments | Decisions taken on false readings | Calibrate before the first watering, then weekly |
A word on how long the equipment lasts, because it changes the arithmetic of a project: according to the University of Florida handbook, perlite and rockwool can be reused for up to three seasons. The support, the line and the gutters last far longer than the substrate, which is why you do not cut corners on their initial assembly.
Setting up your soilless system
JOGOO Agriculture supplies and installs tunnel greenhouses, supports, fertigation lines and substrates for soilless crops in West and Central Africa. See the Agricultural Greenhouses page for the structures and interior equipment, and the Irrigation & Pumping page for the pumping and tank side. For a quote based on your area and your water resource, go through the Contact page.
Frequently asked questions
How much substrate does each plant need in a soilless system?
About 5 litres per plant for fruiting vegetables such as eggplant, sweet pepper or tomato, and 3 to 4 litres for leafy vegetables, according to the province Sud of New Caledonia sheet. The University of Florida handbook goes higher, 9 to 14 litres per plant. A larger volume is more forgiving of a watering outage.
How many drippers does a growing bag need?
One per plant. A bag carrying three plants gets three drippers. In soilless growing the substrate does not redistribute water sideways the way soil does, so a plant without a dripper gets nothing.
What drainage should I aim for, and how do I measure it?
30 percent of the volume applied, according to the province Sud sheet. Put a graduated bucket under the return of one reference row, measure at the same time every day, and record the EC of the drainage as well as its volume.
What EC and pH should the nutrient solution have?
For fruiting vegetables, an EC of 2.5 to 3 in the hot season and 2.8 to 3.5 in the cool season, with a pH of 5.8 to 6.2 according to province Sud. The University of Kentucky uses a pH band of 5.5 to 6.5 for hydroponics in general.
Can the substrate be reused from one season to the next?
According to the University of Florida handbook, perlite and rockwool are reused for up to three seasons. How long depends on the health status of the previous crop and on how much the material has compacted.
Do the bags need a slope, and how much?
Yes. The University of Florida handbook uses about 1 inch per 100 inches of length, which is 1 percent, on solution flow channels. Treat that as a minimum, not a target.
Sources
- Direction du Développement Rural, province Sud de Nouvelle-Calédonie, Culture hors-sol, Perfectionnement 1 : solutions nutritives et irrigation, 2016
- Fenneman D., Sweat M., Hochmuth G., Hochmuth R., Production Systems, Florida Greenhouse Vegetable Production Handbook, vol. 3, HS785, UF/IFAS Extension
- Byrd S., Sharma S., Ying Q., Selecting Growing Media for Soilless Systems, CCD-TA-02, Center for Crop Diversification, University of Kentucky, 2025
