A shade cloth is a specialized fabric used above a greenhouse to manage the internal microclimate by mitigating intense solar radiation. It intercepts a portion of incoming sunlight, which is especially important during the hottest months of the year. This protective layer reduces heat buildup inside the structure, preventing temperatures from causing plant stress and damage. Selecting the correct shade cloth is a matter of balancing light reduction with the specific needs of the plants being grown.
Deciphering Shade Percentage
The primary characteristic of any shade cloth is its percentage rating, which directly measures its light-blocking capability. A 50% shade cloth, for example, blocks 50% of the sunlight that hits its surface, allowing the remaining 50% of light to pass through. This numerical rating is the most important factor in selection, as it dictates the light intensity inside the greenhouse. Common shade cloth increments are 30%, 40%, 50%, and 70%.
The density of the material, or the tightness of its weave, determines this percentage, with a higher number correlating to a denser fabric. Choosing a percentage that is too high can starve plants of light needed for photosynthesis, while a percentage that is too low may not offer enough protection from scorching sunlight or excessive heat. The right choice depends on the plant species and the intensity of the sun in the local geographical area.
Material and Color Choices
The physical construction of the shade cloth material affects both its lifespan and handling characteristics. The two main types are woven and knitted, each offering distinct advantages for greenhouse applications.
Woven shade cloth is typically made from tightly interlocked polypropylene threads, making the fabric stiffer and often heavier. This construction offers high durability and is often chosen for permanent, external installations where maximum strength against wind and hail is desired. A drawback is that if the fabric is cut or damaged, it may be prone to unraveling.
Knitted shade cloth, commonly made from high-density polyethylene, uses an interlocking thread design that allows it to be cut to size without the edges unraveling. This makes it more flexible and easier to install or remove seasonally, often offering better airflow through the material. While highly durable and resistant to tearing, both types are typically UV-stabilized for longevity.
The color of the shade cloth significantly influences the greenhouse environment beyond light reduction.
Black shade cloth absorbs solar radiation, providing uniform shade but potentially increasing the ambient temperature near the cloth. This color choice is often preferred in cooler climates where retaining some heat is beneficial, or for general-purpose shading.
Green shade cloth provides a light spectrum that mimics natural tree shade. It offers a balanced light diffusion for the plants.
White or aluminet shade cloth is highly reflective, bouncing a significant amount of solar energy away from the greenhouse before it can enter. This reflection maximizes the cooling effect, making white the superior choice for hot climates, and it diffuses the light more evenly across the plant canopy.
Matching Shade Levels to Plant Needs
The goal of selecting the appropriate shade percentage is to match the light requirements of the specific crop with the intensity of the sun in the growing region.
High-light, heat-tolerant crops like tomatoes, peppers, and cucumbers require the least amount of shade to maximize fruit production. For these warm-weather vegetables, a shade cloth in the 30% to 40% range is usually sufficient to prevent sunscald and moderate high temperatures. In regions with extremely intense, prolonged summer heat, a 50% shade cloth may become necessary to avoid blossom drop and stress.
General greenhouse crops, which include leafy greens, herbs like basil and cilantro, and common bedding plants, benefit from moderate shading. These plants are susceptible to bolting and scorching in full, intense summer sun. A shade cloth in the 40% to 50% density range strikes a good balance, providing enough light for robust growth while maintaining cooler leaf temperatures.
Delicate, shade-loving plants, such as orchids, ferns, and tropical foliage, require the highest degree of light reduction to mimic their native under-canopy environments. These species thrive when the light is significantly filtered, making shade percentages from 60% up to 80% more appropriate. Seedlings and young cuttings during the propagation phase also benefit from this heavier shading to protect their tender tissues and encourage root development. Regional climate plays a significant role in final selection.