Greenhouse shade cloth is a specialized material designed to manage intense solar radiation entering a controlled growing environment. Its primary function is to reduce light and heat load, preventing plants from suffering sunscald and heat stress during the hottest parts of the year. Selecting the precise shade percentage is crucial for maintaining the optimal light intensity required for healthy growth and maximum yield. Choosing the wrong percentage can either starve sun-loving plants of needed energy or fail to protect delicate species from damaging rays.
Understanding Shade Percentage Ratings
The percentage rating of a shade cloth directly indicates the fraction of solar radiation it blocks from entering the greenhouse structure. For instance, a 30% shade cloth permits 70% of the ambient sunlight to pass through to the plants below. Common density increments typically range from 30% up to 80% to suit varying plant needs.
Light reduction and heat reduction are related but not identical properties of the material. While blocking light inherently reduces the solar energy that converts to heat inside the greenhouse, the cloth’s color also plays a significant role in temperature management. A white or aluminized shade cloth actively reflects solar energy away from the structure, providing a greater cooling effect than a darker cloth of the same percentage, which tends to absorb heat.
Climate and Geographic Factors Influencing Selection
The local environment is a primary consideration that establishes the baseline percentage requirement for any greenhouse operation. Geographic factors, such as latitude and altitude, influence the intensity of sunlight and the duration of high temperatures. Regions closer to the equator or at higher altitudes experience more intense solar radiation, often requiring denser shade cloth.
Growers in northern latitudes or areas with consistently mild summers can utilize lower percentages, such as 30% or 40%, to maximize available light. Local average summer temperatures and the UV index are better indicators of heat stress risk than simple geographical position alone. Areas that routinely see high temperatures may require a denser cloth, around 50% to 70%, to mitigate excessive light and heat buildup inside the structure.
Plant-Specific Recommendations for Shade Cloth
The specific light requirements of the crop being grown are the most important factor in determining the necessary shade percentage. Plants are generally categorized based on the amount of light they require for optimal photosynthesis and growth. Using a cloth that is either too dense or too light can negatively impact productivity and plant health.
Crops that naturally thrive in full sun, often referred to as high-light crops, include fruiting vegetables such as tomatoes, peppers, and cucumbers. These species typically require minimal shading to prevent sunscald during peak summer, making lower percentages of 30% to 40% ideal for their cultivation. This range offers just enough protection to prevent damage without significantly limiting the energy needed for fruit production.
Medium-light crops, which encompass most leafy greens, culinary herbs, and common bedding plants, perform best under moderate shade. For these groups, a shade cloth percentage between 40% and 55% is commonly recommended to strike a balance between light exposure and heat protection. Lettuce, spinach, and many herbs can bolt or wilt under intense midday sun, so this moderate density maintains cooler leaf temperatures.
Finally, shade-loving plants, including orchids, ferns, and cuttings in propagation areas, require substantially filtered light, similar to a forest understory. For these delicate species, a shade cloth density of 60% up to 80% is necessary to avoid scorching their sensitive foliage. This high level of light reduction creates a cooler, more diffused light environment.
Seasonal Timing and Installation Methods
Shade cloth is a seasonal tool, and its deployment should coincide with the onset of high-intensity light and heat, usually in late spring or early summer. Growers install the cloth when the daily UV index consistently reaches a high level, such as 8 or higher, indicating potential plant damage. Conversely, the cloth should be removed in early fall when light intensity naturally decreases, allowing plants to benefit from all available sunlight.
The placement of the shade cloth significantly impacts its effectiveness in heat reduction. Installing the cloth on the exterior of the greenhouse structure is superior because it deflects solar radiation before it can penetrate the glazing and convert into heat. Exterior mounting prevents heat from being trapped inside, which helps maintain lower internal air temperatures. While interior mounting is simpler, it only diffuses the light and does not prevent the solar heat load from entering.