Tomatoes are tender, warm-weather plants highly sensitive to environmental extremes. A successful harvest depends on protecting them from conditions outside their preferred temperature range. Covering tomato plants is a necessary protective measure, extending the growing season and mitigating damage from excessive heat or transplant shock. Knowing precisely when to deploy these covers is essential for ensuring the plants thrive.
Protecting Against Cold and Frost
The decision to cover a tomato plant is most often triggered by a drop in temperature, as tomatoes lack natural cold tolerance. Growers should monitor forecasts closely for evening temperatures dipping toward the 40°F mark. When temperatures fall below 50°F, plants begin to experience chilling injury, which damages cell membranes and slows metabolic processes. Prolonged exposure below this threshold can lead to stunted growth and discolored foliage. Covering becomes an immediate necessity when the forecast calls for temperatures near or below 40°F, as temperatures at or below 32°F cause lethal frost.
A simple overnight covering can provide 4 to 8°F of thermal protection, often enough to prevent fatal damage from late spring or early fall frost. Cold damage is cumulative; repeated exposure to the lower 40s significantly impacts the plant’s health and fruit yield. Temporary covers should be applied in the late afternoon, before the day’s warmth escapes, and removed the following morning once temperatures rise above 50°F to allow for light and air circulation.
Shielding Against Excessive Heat and Sun Scald
While cold is the most common threat, covering tomatoes is also required during periods of intense heat to prevent physiological damage. High temperatures, particularly those consistently above 90°F to 95°F, interfere with pollination and fruit set, a condition called blossom drop. The plant’s reproductive cycle stalls, prioritizing survival over production. Direct, intense sunlight combined with high temperatures can also cause sun scald on the developing fruit.
Sun scald appears as white or yellowed blotches on the side of the tomato exposed to the sun, rendering that part of the fruit inedible. This is common if the plant has lost foliage due to disease or excessive pruning, suddenly exposing the fruit. The solution for heat stress is temporary shade, which is distinct from the heavy coverings used for frost protection.
Shade cloth, typically rated to block 25% to 50% of direct sunlight, filters the sun’s intensity during the hottest part of the day. This filtering reduces the ambient temperature around the plant by several degrees. It mitigates both blossom drop and sun scald without completely halting photosynthesis.
Covering During Transplanting
The third time to cover tomato plants is immediately following transplanting from a sheltered indoor environment to the garden bed. This process can cause significant stress, or “transplant shock,” as the plant adjusts to outdoor conditions. Covering or shading is necessary during the plant’s initial week in the ground to help it acclimate. Transplant shock is exacerbated by rapid changes in temperature, humidity, light, and wind.
Even a few hours of direct, intense sun or wind can cause damage, leading to wilting, yellowing leaves, and stunted growth. The goal of this initial covering is to ease the transition after the “hardening off” period. Using a lightweight, permeable cover for the first three to seven days protects the tender foliage until the plant can establish a strong root system capable of supporting its water needs in the new environment.
Essential Covering Methods and Materials
The specific method and material for covering a tomato plant depend on the type of protection needed. For overnight frost defense, heavy, insulating materials are required, such as thick blankets, burlap, or commercial frost cloth. These materials must be draped over a support structure so they do not touch the foliage, as contact points transmit cold directly to the plant tissue. The cover must extend all the way to the ground and be anchored to trap the heat radiating from the soil.
For added insulation during severe cold, a layer of plastic can be placed over the fabric, but it must be removed promptly in the morning to prevent overheating and moisture buildup. When shading against excessive heat, specialized shade cloth is the only appropriate material. This permeable, woven material allows for air movement and light penetration while diffusing harsh direct sun rays.
Unlike frost covers, shade cloth can remain in place during the day, focusing on reducing light intensity rather than trapping heat. For protecting newly transplanted seedlings, lightweight row covers or cloches offer wind protection and slight thermal insulation. These materials are highly permeable, allowing light and water to pass through, preventing wind burn while mitigating the initial intensity of direct sun exposure.