Tomatoes are heat-loving plants, but intense, direct sunlight and prolonged high temperatures cause significant damage. When temperatures consistently exceed the optimal growing range, plants suffer from heat stress, affecting both health and productivity. Primary concerns include sunscald on developing fruit and blossom drop, which severely limits the total harvest. Strategic shading is a necessary protective measure, especially in climates where summer temperatures frequently climb into the 90s and above.
Recognizing Heat Stress and Timing Shade Application
The need for shade is often signaled by distinct visual cues from the plant. One immediate sign of heat stress is the temporary wilting or curling of leaves, where the foliage rolls inward or upward to reduce sun exposure. While this mechanism helps conserve moisture, sustained curling indicates a more serious problem.
Blossom drop is a major sign of reproductive failure, occurring when the plant aborts flowers before they can set fruit. If air temperatures consistently exceed 90°F during the day or 70°F at night, the pollen often becomes sterile, preventing fertilization. Fruit that does set may develop sunscald, appearing as pale, blistered patches that eventually turn white and leathery. To prevent these issues, install preventative shading when the forecast calls for sustained daily highs above 92°F, rather than waiting for symptoms.
Choosing the Appropriate Shading Material
Selecting the correct material is important, as the shade must reduce heat intensity without inhibiting photosynthesis. The standard choice is specialized shade cloth, rated by the percentage of sunlight it blocks. For tomatoes, the optimal density falls between 30% and 50% shade, balancing protection and light availability.
A 30% to 40% shade cloth is usually sufficient for most hot climates, reducing canopy temperature while allowing 60% to 70% of ambient light to reach the foliage. Using a higher percentage, such as 70%, can be detrimental because it starves the plant of the light energy needed for fruiting and ripening. White or reflective shade cloth is superior at rejecting heat compared to common black material, further lowering temperatures. Alternative temporary materials, such as light-colored netting or lattice structures, can provide filtered light protection. However, these alternatives lack the precise density control of engineered shade cloth.
Constructing and Positioning the Shade Structure
The structure must elevate the shade cloth above the plants to allow for generous airflow, which is important for cooling. A simple, temporary frame can be constructed using materials like PVC pipe and three-way connectors. Alternatively, rebar or wooden stakes driven into the ground can serve as vertical supports. The frame size should be slightly larger than the plant area to prevent the shade cloth from resting directly on the foliage.
Once the frame is secure, drape the shade cloth over the top and fasten it using zip ties, clips, or bungee cords. Ensure the material is taut to prevent flapping in the wind. The most important aspect of installation is the structure’s orientation, which must block the intense afternoon sun. Position the structure to shield the plants primarily from the west and south between approximately 1 PM and 5 PM. This strategic placement allows the plants to receive full, beneficial morning sunlight necessary for robust growth.