Greenhouse
热门新闻
The season starts with the structure, not the crop. After the previous crop is cleared, the house should be cleaned, the substrate replaced or steamed, the drainage lines flushed and disinfected, and the screen, vent and irrigation equipment checked before any plant is ordered. Establish the new crop plan against the delivery calendar, and start the nursery so that strong, evenly sized transplants are ready at planting. Early crop growth is governed by light rather than by feeding, so avoid heavy early fertilisation that produces thin stems and large leaves. Keeping records from the first week, including temperature, humidity, drainage percentage, EC and pH, gives the basis for judging the crop later and is the cheapest diagnostic tool available to a greenhouse manager.
Vegetables grow by day and respire at night, and the day-night temperature difference is one of the most powerful tools available for improving quality and reducing energy use. A difference of roughly six to eight degrees for tomato and pepper encourages compact growth, firm fruit and better stem quality, while a smaller difference in cucumber and basil keeps leaf expansion and shelf life in line with the market. Day temperatures for tomato and pepper are typically held in the low to mid twenties, cucumber slightly lower with more humidity, and lettuce and other leafy greens in the mid teens. Night temperatures are set a few degrees lower to allow assimilate to be transported to fruit and roots rather than respired away, and to allow pollen to shed properly in tomato and capsicum. A night too warm drives vegetative growth and thin fruit, while a night too cold slows the crop, causes pollen problems and drives the heating system hard.
| Crop group | Day temperature | Night temperature | Humidity range |
|---|---|---|---|
| Tomato | 21 to 25 degrees | 16 to 18 degrees | 60 to 70 percent |
| Cucumber | 22 to 26 degrees | 17 to 19 degrees | 70 to 80 percent |
| Sweet pepper | 21 to 26 degrees | 16 to 18 degrees | 60 to 70 percent |
| Strawberry | 15 to 20 degrees | 10 to 12 degrees | 60 to 70 percent |
| Leafy greens | 15 to 18 degrees | 8 to 12 degrees | 65 to 75 percent |
| Basil and herbs | 22 to 26 degrees | 16 to 18 degrees | 65 to 75 percent |
Light is the resource that cannot be bought, so greenhouse design decisions are made around it. Wider spans mean fewer internal shadows and better light distribution, while a clean cover, careful glass maintenance and the removal of too many hanging crop rows keep more light reaching the canopy. Humidity above roughly eighty-five percent for long periods creates the leaf spots and botrytis that end protected crops, and the combination of a cold roof, warm pipe and wet canopy is the classic trigger, so dehumidification is achieved by venting warm moist air and by running heating and venting briefly together rather than by leaving humidity to accumulate overnight. Ventilation capacity is decided by span width and ridge height, and a house with too little vent area cannot hold humidity down in spring and early summer. When vents are closed in winter, carbon dioxide falls to near ambient levels, and where a sealed house is heated to raise levels, enrichment up to around 800 to 1000 ppm raises photosynthesis and yield in tomato, provided humidity and temperature are managed at the same time.
In a recirculating hydroponic system the nutrient solution is the crop's entire food supply and its chemistry must be checked every day. Electrical conductivity is the fast indicator of how much salt is in the root zone, and pH controls how available the nutrients are and how much of the solution the roots actually take up. Rising EC between irrigation cycles indicates that the plant is taking up more water than nutrients, so the correction is to irrigate more frequently rather than to reduce the feed, and falling EC indicates the opposite. Recirculating systems need frequent pH adjustment because uptake is selective: potassium and calcium move at different rates than magnesium and sulphate, so the ratio drifts over time even when the total salt level is stable. Water quality sets the ceiling on everything, and irrigation water should be analysed for alkalinity, bicarbonate, sodium, chloride, hardness and trace elements. Alkaline water drives pH upward and precipitates iron and manganese, so acid injection or an acid-compatible injection pump may be needed to keep the root zone available.
| Parameter | Tomato | Cucumber | Leafy greens and herbs |
|---|---|---|---|
| Target EC in root zone | 2.5 to 3.5 mS per cm | 2.2 to 3.0 mS per cm | 1.0 to 1.8 mS per cm |
| pH range | 5.5 to 6.5 | 5.5 to 6.5 | 5.5 to 6.2 |
| Drainage fraction to target | 10 to 20 percent | 10 to 20 percent | 10 to 15 percent |
| Daily water use per square metre | 3 to 5 litres | 4 to 6 litres | 1.5 to 3 litres |
| Key risk in recirculation | Calcium and salinity | Salinity and wilt | Root temperature |
Irrigation in a greenhouse is decided by the crop's daily demand, which changes with light, temperature, growth stage and root volume, and by the drainage that confirms the root zone has been wetted evenly. A practical routine is to irrigate early in the day, using small frequent pulses rather than one large application, so that the root zone is wetted uniformly and the excess leaves the root zone before the day heats up. Measuring drainage rather than guessing is what makes the difference: a collection sample taken at the end of the run should show the EC of the drainage slightly above the feed, and the drainage fraction should sit at the target. Water use per square metre per day for a fruiting crop typically lies between three and six litres in the peak of summer, higher in glass houses with evaporative cooling. Recycling drainage through filtration and disinfection, or using drip-on-substrate with collection, cuts consumption substantially and reduces the fertiliser load leaving the site, while a simple rainwater buffer can supply part of the irrigation demand in areas with reliable rainfall.
A greenhouse is a favourable environment for pests because temperature and humidity are managed for the crop and there is little natural habitat for predators, so prevention has to be built into the system. Monitor with yellow and blue sticky traps placed at plant height, checked weekly and mapped by zone so that a hotspot is identified before it spreads. Common problems in protected vegetables include whitefly, thrips, aphids, spider mite, leaf miner and cyclamen mite, each of which responds differently to humidity, temperature and beneficial insects. Biological control works well in warm, long-cropping houses where the ecosystem is stable, with parasitic wasps for whitefly and leaf miner, predatory mites for spider mite and, where policy permits, entomopathogenic fungi for aphids and thrips. Sanitation at the end of the crop, a clean start and steady monitoring remove most outbreaks.
In a vegetable greenhouse the labour plan is part of the production plan. Peak demand for hands falls during pruning, tying, pollination, spraying and harvesting, and a house with continuous long crops needs a stable crew with defined daily tasks. Harvesting is often the largest single labour cost, so it should be designed around flow: pick crates and field boxes sized to move through the paths, trolley routes that avoid walking on beds, and grading tables placed close to the exit. Packing should happen in a cooled area, because vegetables harvested warm lose quality quickly. Most fruiting crops are harvested into shallow trays rather than deep crates, to avoid bruising, and leafy greens and herbs are hydro-cooled or vacuum-cooled promptly to hold field heat out of the leaf. Herbs are bunched and packed with high humidity to prevent desiccation, strawberries and cherry tomatoes are cooled quickly and packed in a rigid tray to prevent compression, and tomatoes are picked with a short stem attached for shelf life. A well-designed house removes the crop from the greenhouse in under twenty minutes from the picking moment to the cold room, and it keeps grading and dispatch moving at the same rate as picking.
Heated greenhouses consume the largest share of operating cost in most vegetable businesses, so heat saving pays back faster than any yield increase. Wall insulation, double glazing on gables and a properly sealed cover reduce the load further. Heating systems should be sized on a design winter condition, and the control strategy should use temperature differentials, night set points and a crop-based schedule rather than a fixed boiler output. Warm air distribution above the crop combined with under-crop pipes raises utilisation of every unit of fuel. Buffer storage of hot water and heat recovery from exhaust air reduce the running hours of the boiler and shorten the payback on the plant. On the revenue side, the same measures that save energy usually improve output, because a stable root-zone temperature and a stable humidity raise the marketable percentage of the crop.
| Measure | Effect on the crop | Effect on operating cost |
|---|---|---|
| Night energy screen | Stable night temperature, better fruit set | Large reduction in night heat loss |
| Root-zone heating pipe | Steady root activity, better uptake | More efficient than heating the air only |
| Heat recovery and buffer tank | Fewer cold starts | Lower boiler hours and fuel use |
| Ventilation and dehumidification | Fewer leaf diseases, firmer fruit | Reduces crop losses and waste |
| Recirculating fertigation | Steadier nutrition, fewer stress periods | Lower water and fertiliser use |
| Improved layout and access paths | Faster harvesting, less damage | Lower labour cost per kilogram |
The target depends on the crop. Tomato and sweet pepper are usually held at roughly 21 to 25 degrees by day and 16 to 18 degrees at night, cucumber at about 22 to 26 degrees by day with higher humidity, and leafy greens in the mid teens by day with cooler nights. Maintaining a day-night difference of six to eight degrees generally improves stem quality and fruit firmness, and it also reduces the heating load, since the structure does not need to recover as much heat each morning.
In a recirculating hydroponic system, pH should be checked every day and EC at least every day during peak growth, with continuous inline monitoring as a useful upgrade. The most informative measurement is the EC of the drainage rather than only the feed, because it shows what the roots have actually taken up. In a drain-to-waste system with small crops, weekly checks of feed EC with monthly checks of drainage are usually sufficient.
Most yield losses trace back to climate imbalance rather than nutrition: condensation and high humidity causing leaf disease, nights too warm driving excessive vegetative growth, or poor pollination reducing fruit set. Root-zone problems such as salinity, low root temperature and oxygen starvation in saturated substrate are the next most common cause, followed by weak pollination in tomato, pepper and strawberry during low-light or high-humidity periods. Regular measurement of temperature, humidity, drainage, EC and pH detects these problems early.
Insulation first, equipment second. An energy screen used every night is usually the fastest payback in the house, followed by sealing and insulating the cover, wall insulation and double glazing, and then by better heat distribution through warm air and root-zone pipes. Heat recovery, hot water buffer storage and a crop-based heating schedule with proper set points reduce boiler hours further. Supplementary lighting in the darkest months usually pays back faster than heating more floor area, because it increases yield per square metre.
相关文档
