Greenhouse
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The structure you build sets the temperature range, light level and humidity ceiling that every crop inside it must live with, so greenhouse selection is really crop selection in reverse. A simple single-span plastic house is excellent for warm-season fruiting crops such as tomatoes, cucumbers, peppers and eggplants during a frost-free window, but it offers little control over winter temperature or summer humidity. A multi-span plastic greenhouse with side ventilation, thermal screens and integrated heating extends the season and raises the yield potential of long-cropping cucumber and tomato programmes. A glass house with permanent heating, CO2 enrichment and continuous hydroponic rails supports year-round production of high-value crops such as cherry tomatoes, specialty peppers, strawberries and herbs for year-round supply contracts. Plants that need warmth and humidity, such as cucumber and basil, behave very differently from crops that prefer cool, bright and airy conditions, such as lettuce and strawberry.
Multi-span plastic greenhouses are the workhorse of protected vegetable production because they deliver a wide span, cheap thermal mass and cost-effective ventilation. They suit crops that occupy a house for most of the season and repay the structure through volume. Tomatoes, both beefsteak and cluster types, form a strong long-crop programme because the stem can be trained upward for eighteen months or more, while grafted cucumbers exploit the vertical space even more aggressively and produce very high output per square metre. Sweet pepper and eggplant need more light and a drier atmosphere than cucumber, so they perform best in the widest spans with good ventilation and floor heating, and they are commonly scheduled in two crop cycles a year where winter light allows. The house should also allow for a nursery area or separate propagation house, since vegetable programmes depend on a reliable supply of uniform transplants rather than on direct sowing into the production bays.
| Crop | Best suited structure | Typical planting density | Main design constraint |
|---|---|---|---|
| Beefsteak tomato | Multi-span plastic or glass | 2.5 to 3.5 plants per square metre | Height and lighting for fruit size |
| Grafted cucumber | Multi-span plastic or glass | 1.2 to 1.6 plants per square metre | Humidity control and high transpiration |
| Sweet pepper | Multi-span plastic, low winter light | 3 to 4 plants per square metre | Light and moderate root-zone temperature |
| Eggplant | Heated multi-span | 1.5 to 2 plants per square metre | Day-night temperature difference |
| Leafy greens and lettuce | Plastic house with benches | 25 to 40 plants per square metre | Cool temperature and airflow |
| Herbs such as basil | Plastic or glass | 10 to 16 plants per square metre | Humidity and leaf quality |
| Strawberry | Glass house with heating | 12 to 18 plants per square metre | Winter light and pollination |
| Seedlings and transplants | Dedicated plastic house | Per tray or gutter | Uniformity and sanitation |
Glass becomes a rational choice when the crop value justifies a permanent structure and the market rewards year-round consistency. The advantages are predictable: light transmission stays high through the season, roof vents and gutters allow larger ventilation openings, heating pipes can be installed under the crop for root-zone temperature control, and screens can be deployed nightly without the dimensional compromises of plastic film. For high-wire tomato and cucumber programmes, a glass house with a 4.5 to 5 metre gutter height and continuous rails is the standard platform, because the crop is trained upward and fruit must hang clear of the floor to avoid soil contact and disease. Specialty peppers, cherry tomatoes and herbs also reward glass, as the environment can be held steady while the market expects weekly delivery.
Soilless cultivation removes the uncertainty of soil-borne disease and allows a much higher degree of control over water and nutrients, which is the foundation of predictable yield. The main families are Dutch buckets or pots, continuous troughs, slab or bag systems, and nutrient film technique channels, with drip irrigation on soil or substrate still common in lower-cost regions. Buckets and troughs suit high-wire tomato, cucumber, pepper and strawberry because the volume of substrate per plant is large and the crop is long-lived. Slabs and bags offer good air-to-water ratio control and are widely used for tomato, pepper and cucumber, with drain collection allowing the grower to steer the root zone by adjusting the irrigation frequency. NFT channels suit leafy greens, pak choi, basil and seedlings, where roots are small and the system must deliver water quickly and evenly over short distances. A recirculating system should include a mixing tank, stock solution dosing, filtration, disinfection and drainage collection, because once nutrients are recirculated the margin for error on EC and pH becomes much smaller.
| System | Typical crops | Relative water use | Nutrient management note |
|---|---|---|---|
| Dutch bucket or pot | Tomato, cucumber, pepper, eggplant | Low to moderate | Large root volume, slow fertigation cycles |
| Continuous trough | Tomato, cucumber, strawberry | Low | Needs levelling and end-of-row drainage |
| Slab or grow bag | Tomato, pepper, cucumber | Moderate | High air-to-water ratio, easy drainage measurement |
| NFT channel | Leafy greens, herbs, seedlings | Very low | Continuous flow, sensitive to pump failure |
| Drip on substrate | Tomato, pepper, cucumber | Moderate to high | Salt accumulation risk in the root zone |
A production calendar turns a greenhouse into a predictable business. Start from the market: decide the delivery windows, the varieties and their crop times, then work backwards through nursery, planting, pruning, pollination, harvest and clean-down. Long crops such as high-wire cucumber and beefsteak tomato are planned as a single planting cycle that may run for twelve to eighteen months, with a short overlap at the end to avoid a supply gap. Shorter crops such as lettuce, pak choi, basil and seedling batches are planned as repeated succession blocks, usually two to five weeks apart, timed so that the harvest of one block coincides with the establishment of the next. Rotation inside a house is limited but not irrelevant. Reusing the same substrate and the same irrigation line for the same species year after year encourages root pathogens such as Pythium, so a sensible rotation alternates plant families, moves crops to different houses where possible, and includes a crop-free interval for disinfection.
Density is a yield-versus-quality decision, not a maximum. Crowding raises total output per square metre in the short term but reduces light capture per leaf, restricts airflow, increases humidity around the canopy and magnifies disease pressure. Wide row spacing and leaf-to-leaf spacing in the row is what allow light to reach the lower leaves that carry the profitable fruit. Tomato crops are commonly planted in double rows at roughly 1.6 to 1.8 metres within-row spacing on 1.2 to 1.4 metre centres, giving a pair of rows per bed with generous access paths for pruning and harvesting. Cucumber is often grown in a single wide row or a double row on beds of 1.0 to 1.2 metres, with vines trained to a leaning or hanging system. Peppers are commonly planted in a double row on 1.4 to 1.6 metre beds because the crop needs light over its whole canopy.
| Crop | Plants per square metre | Row spacing | Plants within row |
|---|---|---|---|
| Tomato, high-wire | 2.5 to 3.5 | 1.2 to 1.4 m | 1.6 to 1.8 m |
| Cucumber, long vine | 1.2 to 1.6 | 1.0 to 1.2 m | 1.6 to 1.8 m |
| Sweet pepper | 3 to 4 | 1.4 to 1.6 m | 0.5 to 0.7 m |
| Strawberry | 12 to 18 | 1.0 to 1.2 m | 0.3 to 0.4 m |
| Leafy greens | 25 to 40 | 0.4 to 0.6 m | 0.25 to 0.35 m |
| Basil | 10 to 16 | 0.6 to 0.8 m | 0.35 to 0.5 m |
Training is a design requirement rather than a routine task, because the wire, hook, clip and trellis system must be specified before the crop is planted. High-wire tomato crops are trained to a single stem, with side shoots removed weekly and the plant leaned or twisted along the support wire so that the head stays within reach of the worker. Cucumber is usually trained to a single stem with laterals and flowers removed according to the plant's position in the row, and the leader is then topped once the head reaches the wire, which keeps fruit quality uniform. Peppers are shaped into two or three stems, removing the first fork and any weak inner shoots, and are supported with soft ties or cages. Basil and other herbs are pinched regularly to keep the crop leafy rather than woody. Leaving the plant canopy open is also a disease-control measure, since a well-spaced, well-trained crop dries faster after irrigation and after condensation forms on the roof, which greatly reduces the leaf diseases that terminate protected tomato and cucumber programmes.
Most protected vegetables depend on pollination for a commercial fruit set. Bees work best at moderate temperatures with adequate light, so hives are introduced once the crop is well established, and boxes are moved after the first two or three trusses so that the bees follow the flowering front. Some tomato varieties, particularly the beefsteak types grown in high-wire houses, can set fruit parthenocarpically at warm temperatures, and growers often combine that with reduced pollination pressure, while others still need insect visits. Hive placement matters as much as hive numbers, since bees forage poorly when temperature rises above roughly 30 degrees or when humidity is very high, and a colony placed in a cold corner of the house will not work for the crop block beside it. Temperature control during flowering is therefore a pollination control measure in its own right, and growers who report poor fruit set usually find the cause in the climate rather than in the crop.
For tomatoes, cucumbers and peppers, a multi-span plastic greenhouse with side and roof vents, thermal screens and integrated heating gives the best balance of capacity and cost, and it can be upgraded to glass-grade climate control as the crop programme matures. For year-round high-value crops such as strawberry, specialty pepper and herbs, a glass house with permanent heating, CO2 enrichment and hydroponic rails is the more profitable platform because it holds a stable climate through the coldest and brightest months. The choice should follow the crop value and the delivery contract rather than the initial capital cost alone.
Cucumber and tomato are the usual starting crops because their training, pruning and pollination systems are well documented, their market demand is broad and their yield response to climate control is easy to measure. Basil, lettuce and pak choi are good short-cycle additions for filling the gap between blocks or for a separate plastic house with rolling benches. Strawberry and eggplant are higher-risk for a first programme because they are more sensitive to climate swings and require tighter management of temperature and root-zone conditions.
Density depends on crop, system and target fruit size. High-wire tomato and cucumber are grown at roughly 1.2 to 3.5 plants per square metre, peppers at 3 to 4, lettuce at 25 to 40 and strawberry at 12 to 18. The correct approach is to start at the lower end of the recommended range, confirm that light and ventilation meet the crop requirement at that density, and only then increase plant number to lift output per square metre.
Yes, provided the system is designed for uniformity and the grower is prepared to measure drainage, EC and pH routinely. Recirculation cuts water and nutrient consumption substantially compared with discharge systems and limits fertiliser loss to the environment, but it also concentrates risk, since a dosing, filtration or disinfection fault affects the whole crop at once. Buckets, troughs and slabs suit long fruiting crops, while NFT channels suit leafy greens, herbs and seedlings with small root systems.
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