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An agricultural greenhouse does not do the same job in tropical Africa as it does in Europe. In a hot climate, the structure is not there to warm the crop: it is there to protect it from driving rain, wind, excessive radiation and virus-carrying insects, while getting rid of heat that builds up very quickly under plastic. Greenhouses suited to the tropics are therefore first and foremost ventilation structures. A closed structure that is too low, badly oriented or covered with an overly fine net will produce less than a well-managed open field. This guide covers the types of structure available, the design parameters that actually determine the outcome, and what trials in Benin and Senegal have shown.
1. What a protective structure really changes in a tropical climate
The first measurable effect of a structure in a hot zone is thermal, and it goes the wrong way. In trials in southern Benin on off-season tomato grown under insect-proof netting, the temperature under the structure rose by 4 to 6 °C compared with outside, with relative humidity held between 70 and 80% (Mensah et al., 2016). A Senegalese trial at the ISRA/CDH station in Sangalkam on cabbage and tomato reached the same conclusion: conditions under the net are hotter and more humid than in the open air (Correa, 2018).
This extra heat is not a deal-breaker, but it imposes a design rule: above a maximum temperature of 27 °C, a multi-span structure must be ventilated permanently, and closable vents are only justified in regions where minimum temperatures fall below 12 °C (Baudoin and von Zabeltitz, Acta Horticulturae 578). In West and Central Africa, none of our vegetable production zones meets the second condition. In other words: permanent openings, always.
The second effect is on plant health, and it is what justifies the investment. A net with the right mesh physically blocks whiteflies, aphids and leaf miners, which reduces both direct damage and virus transmission. The Benin trial produced marketable tomatoes free of pesticide residues, a selling point few open-field growers can claim.
2. The main types of agricultural greenhouse
Four structural forms are documented for tropical regions: the simple hoop tunnel, the raised arch, the two-pitch (gable) structure and the offset-pitch structure, known as split-gable or split-arch, which provides a permanent ridge opening (CARDI, 2014). In practice, on farms in West and Central Africa, you mainly find:
- The simple plastic tunnel. The cheapest and most widespread, and also the most prone to overheating if its sides are not open. Suitable for nurseries and short off-season cycles.
- The net house, or screenhouse. Fully covered in insect-proof netting, without plastic, sometimes with a limited plastic roof to keep rain off. This is the most consistent solution in a hot, humid climate: it protects against pests without trapping as much heat as continuous sheeting.
- The shade house. Shade netting only, designed to reduce radiation on sensitive crops and nurseries. It protects neither against rain nor against insects.
- The multi-span greenhouse. Several bays joined by gutters, for professional-scale areas. It demands serious ventilation design, with ridge openings.
3. The five design parameters that decide the outcome
Choosing an agricultural greenhouse comes down to figures, not a catalogue. The recommendations below come from the reference manual for tropical greenhouse growing published by CARDI.
3.1 Opening area
For a naturally ventilated greenhouse, the roof opening area must equal 20% of the floor area (CARDI, 2014). This is the rule most often ignored in the field: a 300 m² tunnel therefore needs about 60 m² of high-level opening, not two doors at the ends.
3.2 Height
A buffer volume of air is needed above the crop: a minimum height of 1.60 m for a structure open at the sides, and at least 3 m for a fully enclosed structure (CARDI, 2014). Low tunnels sold as budget options literally cook the crop in the dry season.
3.3 Orientation
In a tropical climate, a single-span greenhouse is oriented east to west, while a gutter-connected multi-span is oriented north to south (CARDI, 2014). Orientation is then adjusted to the site’s prevailing winds, since natural ventilation depends on them first and foremost.
3.4 Dimensions
For an enclosed structure with passive ventilation, the recommended maximum width is about 10 m, with a length of about 22 m (CARDI, 2014). Beyond that, the air in the centre is no longer renewed and you have to switch to mechanical ventilation, and therefore to energy.
3.5 Net mesh size
To exclude whitefly, the mesh opening must not exceed 0.29 mm, which corresponds to a 58 mesh net; the same net also stops aphids and leaf miners (CARDI, 2014). Beware of the trade-off: the finer the net, the more it restricts air movement, a point explicitly raised in work on structures for smallholders in tropical regions (Baudoin and von Zabeltitz). A fine net therefore calls for a taller, more open structure, not the reverse.
4. What West African trials show
Two results are worth reading together, because they say different things.
In southern Benin, off-season tomato grown under insect-proof netting reached marketable yields of around 50 to 57 t/ha, with a clear reduction in bird pressure and production free of any pesticide residue risk. The economic analysis from the same work shows a considerable gap depending on the sales channel: a net margin of 407 FCFA/kg on the organic market against 7 FCFA/kg on the conventional market (Mensah et al., 2016). The market outlet therefore matters as much as the technique.
In Senegal, the dry-season trial at Sangalkam on cabbage and tomato gives a more sober result: installing nets did not change yield, apart from a positive effect on the number of tomato fruits with a mosquito-type net. Above all, the nets reduced infestations of large insects such as noctuid moths, but favoured small pests, notably aphids, with associated yield losses, and limited colonisation by natural enemies (Correa, 2018).
The lesson is clear: a protective structure is not a product, it is a system. It removes part of the pest pressure and creates another. Without aphid monitoring, without introducing or conserving beneficial insects and without managing the growing environment, the investment does not pay back. This is exactly the integrated pest management logic we apply in crop protection, and that we detail, for example, for tomato late blight in tropical climates.
5. Which crops make a greenhouse pay
An agricultural greenhouse only pays for itself with high-value crops sold out of season or into a quality segment. The usual candidates in West and Central Africa are off-season tomato, sweet pepper, cucumber, lettuce and herbs, as well as nursery seedling production, which remains the safest use for a first structure. Field food crops have no place under cover.
To weigh up species and their margins, our feature on vegetable farming in Africa compares yields and costs per hectare, and the tomato planting guide sets out the full crop management sequence from sowing to harvest.
6. Greenhouse and soilless growing: two separate decisions
Many project developers confuse greenhouses with soilless growing. They are two independent choices. You can grow in the ground under cover, which remains the most accessible option, and you can run a soilless system under a simple shade house. Soilless growing is justified when the soil is contaminated, saline or absent, not because a greenhouse has been built. Systems, installation costs and profitability conditions are covered in our feature on soilless growing and hydroponics in Africa.
7. Irrigation and fertilisation under cover
Under cover, rain no longer gets in: all of the crop’s water needs become your responsibility, and localised irrigation is no longer an option but an operating requirement. Drip irrigation is the clear choice for three reasons: it delivers water to the base of the plant without wetting the foliage, so it does not encourage disease in an already humid environment; it allows fertigation; and it limits weed growth between rows. Our guide to the drip irrigation system covers sizing and costs, and our irrigation and pumping teams handle design and installation.
On the nutrition side, feeding must be split and adjusted to the growth stage, since the volume of soil explored is often smaller and leaching is no longer driven by rainfall. Standard formulas and rates by crop are set out in our guide to NPK, foliar and organic fertilisers.
8. The most expensive mistakes
- Closing the structure to protect the crop better, and turning it into an oven. Protection comes from the mesh, not from being airtight.
- Choosing a low structure to save on hoops, then losing the crop in the dry season.
- Fitting a fine net without increasing the opening area, which cancels out natural ventilation.
- Neglecting anchoring and wind resistance: in tropical zones, violent rain and gusts are the leading cause of destruction of light structures.
- Reusing soil already cropped with solanaceous crops without rotation or disinfection, and concentrating soil-borne pathogens under cover.
- Building before securing a market, when the Benin trial shows that margin depends first on the sales channel.
9. Sizing your project
A serious greenhouse project starts with three pieces of information: the site’s microclimate, including prevailing winds and maximum temperatures; the target crop and its off-season calendar; and the market outlet and expected price. Everything else (structure, mesh, ventilation, irrigation) follows from these. JOGOO Agriculture designs and installs agricultural greenhouses suited to conditions in sub-Saharan Africa, and supports project developers along the whole chain, from feasibility study to first production, through its turnkey agricultural projects and agricultural consulting and engineering services.
Sources and references
- CARDI (2014). Tropical Greenhouse Growers Manual for the Caribbean. Caribbean Agricultural Research and Development Institute.
- Mensah A., Simon S., Assogba Komlan F., Adjaïto L., Martin T., Ngouajio M. (2016). Intensification de la culture de tomate sous abri couvert de filet anti-insectes en région chaude et humide du Sud-Bénin. Science et Technique, Revue burkinabè de la recherche, série Sciences naturelles et agronomie, no. 2, pp. 267-283.
- Correa P. (2018). Potentiel de la lutte physique en maraîchage au Sénégal et impact sur la régulation naturelle. Université Cheikh Anta Diop de Dakar, trials conducted at the ISRA/CDH station in Sangalkam.
- Baudoin W. O., von Zabeltitz C. Greenhouse Constructions for Small Scale Farmers in Tropical Regions. Acta Horticulturae 578, pp. 171-179, International Society for Horticultural Science.
Article written by the JOGOO Agriculture agronomy team. Design recommendations must be adapted to the microclimate, prevailing winds and target crop on each site.
Frequently asked questions
How much opening area does a greenhouse need in a tropical climate?
For a naturally ventilated greenhouse, the roof opening area must equal 20% of the floor area, according to CARDI’s tropical greenhouse manual. A 300 m² structure therefore needs about 60 m² of high-level opening, in addition to the side openings.
Does a greenhouse raise the temperature in a hot climate?
Yes. Trials in southern Benin on tomato under a net house measured a rise of 4 to 6 °C compared with outside, with relative humidity of 70 to 80%. That is why ridge height and opening area are the first two selection criteria in tropical zones.
Which insect net mesh size should you choose?
To exclude whitefly, you need a mesh opening of no more than 0.29 mm, which is a 58 mesh net, and it also stops aphids and leaf miners. This fine net does, however, reduce air movement: it calls for a taller structure and more openings.
Does a greenhouse always increase yield?
No. The Senegalese trial at Sangalkam observed no change in cabbage and tomato yield under nets, and recorded an increase in aphids as well as reduced colonisation by natural enemies. A structure shifts pest pressure rather than removing it, and must be managed with integrated pest management.
Which crops should you grow in a greenhouse in West Africa?
High-value crops sold out of season: off-season tomato, sweet pepper, cucumber, lettuce, herbs, as well as nursery seedling production. Field food crops have no economic case under cover.
Do you have to grow soilless in a greenhouse?
No. Growing in the ground under cover remains the most accessible option. Soilless growing is justified when the soil is contaminated, saline or unavailable, regardless of whether there is a greenhouse.
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