Tomato plants are sensitive to environmental shifts and require careful management for a successful harvest. As warm-season crops, they are highly susceptible to damage from sudden temperature drops, intense sunlight, and various garden pests. Employing the correct covering material provides a necessary protective microclimate. Understanding the specific function of each cover—insulation, pest exclusion, or heat reduction—is paramount for the plant’s health and productivity.
Materials for Short-Term Cold Protection
Protecting tomato plants from unexpected late-spring or early-fall frost is the most common reason for using temporary coverings. The primary goal is not to generate heat, but to trap the residual warmth radiating from the ground throughout the night. This heat-trapping mechanism provides a few degrees of protection when temperatures dip near or below freezing.
Specialized materials, known as frost blankets or row covers, are often made from lightweight, spun-bonded polyester or polypropylene fabric. These commercial covers can provide a temperature increase of approximately 4 to 8°F, depending on the material’s weight. For more severe cold snaps, a heavier blanket can offer up to 10°F of protection.
Household items like old bed sheets, blankets, or towels can serve as effective temporary covers when secured firmly. It is important to drape the material over a support structure, such as a tomato cage or stakes, to prevent the fabric from touching the foliage. Direct contact with the leaves when frost forms can transfer the cold and cause damage to the plant tissue.
Plastic sheeting can also be used, but it must be kept strictly off the plant material, as it is a poor insulator and transfers cold immediately. All temporary covers must extend to the ground and be secured around the perimeter with soil, rocks, or bricks to prevent stored ground heat from escaping. These insulating covers must be removed promptly the following morning to allow for air circulation and sunlight exposure, preventing the plants from overheating or developing fungal issues.
Protective Fabrics for Pest Exclusion
Lightweight fabrics create a physical barrier against common garden pests without blocking necessary sunlight and moisture. These materials, often called floating row covers, are typically fine mesh or very light spun-bonded material, weighing around 0.45 to 0.6 ounces per square yard. This low density allows for high light transmission, often 85% to 95%, which is sufficient for healthy plant growth.
The fine weave of the fabric is effective at excluding flying insects like flea beetles, aphids, and the moths that lay eggs for tomato hornworms. To maintain the barrier and protect the plants from crushing, these covers are supported by flexible hoops or wire frames that arch over the planting row. The edges of the cover must be thoroughly buried or weighted down to prevent pests from crawling underneath.
Using these fabrics early in the season prevents egg-laying before pest populations grow large. However, if the tomato flowers are in bloom, the cover must be temporarily lifted during the day to allow access for pollinating insects.
Managing Intense Heat With Shade Cloth
Tomato plants suffer stress when daytime temperatures consistently exceed 85°F, leading to problems like sunscald on the fruit and blossom drop. To mitigate this, shade cloth is used to reduce the intensity of solar radiation. Shade cloth is measured by its density, which indicates the percentage of sunlight it blocks.
For tomatoes, a shade cloth density between 30% and 40% is recommended, as it filters enough light to prevent damage without hindering photosynthesis. This material is typically draped over a fixed frame or arbor, ensuring it remains suspended above the plants. The structure allows for continuous airflow, which is important for lowering the ambient temperature around the foliage.
The strategic placement of the shade cloth is timed to coincide with the hottest hours of the day, typically between 10 a.m. and 4 p.m. Reducing direct exposure during peak heat helps prevent the fruit from developing white or yellow patches characteristic of sunscald. Moderating the canopy temperature also prevents the heat-induced abortion of flowers, supporting better fruit set.