🌤️ Greenhouse Environment

A greenhouse is useful only if it creates a better crop environment than the open field. That means the structure alone is not enough; what matters is how well the grower manages light, temperature, humidity, air movement, and carbon dioxide around the crop.

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Why Greenhouse Environment Matters

Crop performance depends on heredity as well as microclimate. In open-field farming, only a few factors can be modified effectively. Inside a greenhouse, far more environmental factors can be influenced together.

The main greenhouse environment components are:

1. light
2. temperature
3. relative humidity
4. ventilation
5. carbon dioxide concentration
6. root-zone conditions

Greenhouse management is basically microclimate management for crop growth.

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Light and Photosynthesis

Light supplies the energy needed for photosynthesis. In the presence of chlorophyll, plants use light, carbon dioxide, and water to produce carbohydrates.

Important points:

• too little light reduces photosynthesis and slows growth
• too much light may injure plant tissues or create heat stress
• light quality also matters, not just intensity

The most useful range for photosynthesis is the visible range, roughly 400 to 700 nm.

Light band	Plant relevance
UV below about 400 nm	Excess amounts may injure plants
Visible light 400-700 nm	Main photosynthetic range
Blue light	Encourages compact, sturdy growth
Red light	Promotes elongation and influences flowering responses
Infrared	Mainly heat effect, not major photosynthetic use

The photosynthetically active radiation range is mainly 400-700 nm.

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Temperature and Crop Growth

Every crop has a favorable temperature range. Below that range, life processes slow or stop; above it, enzymes and plant metabolism are disturbed.

Temperature influences:

• photosynthesis
• respiration
• flowering
• fruit set
• crop duration

Greenhouse crops are often managed with slightly higher day temperatures than night temperatures. This differential supports balanced growth and more efficient crop development.

Good greenhouse temperature management is not about keeping the house simply "warm." It is about keeping the crop within an optimum range.

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Relative Humidity

Relative humidity inside a greenhouse is usually higher than outside because crops continuously add water vapor through evapotranspiration.

High humidity can:

• reduce transpiration
• favor some diseases
• interfere with pollination in certain crops

Low humidity can:

• increase water stress
• cause excessive transpiration
• reduce plant turgidity

For many greenhouse crops, a moderate humidity range is desirable, while nursery or propagation work may require much higher humidity.

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Ventilation

Ventilation is essential because greenhouse air must be renewed and regulated. It performs several jobs at once:

1. removes excess heat
2. lowers excessive humidity
3. replenishes carbon dioxide
4. improves air movement around plants

Ventilation may be:

• natural, through vents and structural design
• forced, through fans and mechanical systems

Ventilation is not only for cooling; it also helps manage humidity and carbon dioxide supply.

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Carbon Dioxide and Crop Productivity

Carbon dioxide is a raw material for photosynthesis. Although the atmosphere normally contains a small amount of CO2, greenhouse crops can rapidly deplete it during active daylight photosynthesis.

When CO2 inside the greenhouse falls too low:

• photosynthesis slows
• plant growth is restricted
• yield potential drops

Ventilation can restore CO2 toward ambient levels. In some intensive systems, CO2 enrichment is used to support higher productivity.

Most greenhouse crops respond favorably when CO2 is maintained above the depleted level produced by the crop canopy under strong light.

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Greenhouse Environment as a System

Environmental factors cannot be managed separately in practice. For example:

• high light often raises temperature
• cooling methods influence humidity
• ventilation affects both temperature and CO2
• irrigation and rooting media influence humidity and root-zone behavior

So greenhouse management is a systems problem, not a single-factor problem.

Summary Cheat Sheet

Factor	Main role	Key concern
Light	Drives photosynthesis	Too little slows growth; too much may cause stress
Temperature	Controls metabolic activity	Each crop has an optimum range
Relative humidity	Affects transpiration and disease	Too high favors disease; too low stresses plants
Ventilation	Removes heat and renews air	Needed for cooling, humidity control, and CO2 supply
CO2	Raw material for photosynthesis	Can become limiting inside closed houses
Root zone	Supports water and nutrient uptake	Must match above-ground environmental control