Gardeners often consider plastic sheeting to protect plants from environmental stress, such as unexpected cold or early frost. While plastic is a common option for creating a sheltered environment, its safe use requires strict caveats. Successful use depends on understanding how the material interacts with light, temperature, and moisture, as failing to follow safety protocols can cause more harm than the weather itself.
Primary Goals for Plastic Plant Covers
Gardeners primarily use plastic sheeting for two goals: short-term temperature defense and long-term season extension. For a sudden, overnight dip in temperature, a temporary plastic cover traps heat radiating from the soil, offering frost protection. This temporary use involves draping the plastic over a plant or frame for the duration of the cold event.
The second use is creating a structural barrier, such as a low tunnel or cold frame, for season extension. This method establishes a warmer microclimate, allowing for earlier spring planting or later fall harvesting. The structural covering allows solar radiation to pass through, warming the air and soil inside the enclosure and adding several weeks to the gardening season.
Essential Design for Safe Covering
Safe and effective use requires a deliberate structural design to prevent damage. A fundamental rule is that the plastic must never directly touch the plant foliage. Cold plastic contacting leaves transfers freezing temperatures, causing cell damage or “burns” where moisture has collected.
To maintain this separation, gardeners must use hoops, stakes, or sturdy frames to support the sheeting, creating an insulating air gap above the plants. Proper ventilation is necessary to regulate the internal environment. The cover must be vented daily during sunny periods to release excess heat and moisture, preventing rapid temperature spikes that can kill plants. Finally, the edges must be anchored securely against the ground using clips, soil, or rocks to seal the enclosure and prevent cold air drafts.
Risks of Improper Plastic Use
Ignoring precise setup and daily monitoring introduces severe risks that can quickly damage plants. The most immediate danger is solarization, which is extreme overheating caused by the greenhouse effect. Clear plastic traps solar energy, causing temperatures inside the enclosure to rise rapidly, potentially reaching lethal levels even if the ambient air is cool. This “cooking” effect stresses plants, leading to wilting and sunscald if the plastic is not vented promptly.
A secondary risk comes from the buildup of moisture and lack of air circulation. An overly humid, stagnant environment is an ideal breeding ground for plant pathogens like mildew, mold, and rot-causing fungi. This combination of trapped moisture and high humidity can lead to fungal diseases or “damping off” in young seedlings, resulting in plant death.
Non-Plastic Options for Plant Protection
Several non-plastic alternatives offer effective plant protection for gardeners who find plastic monitoring too cumbersome. The most common alternative is horticultural fleece, also known as floating row cover, a lightweight, spun-bonded fabric. This material can be laid directly over plants or supported by hoops, providing frost protection while allowing light, air, and moisture to pass through.
Heavier materials like thick blankets, burlap, or old bedsheets can be draped over plants for temporary overnight frost protection. Individual plants can also be shielded using small, bell-shaped glass or terracotta cloches, which create a stable microclimate. These materials are less prone to causing overheating and moisture buildup because they offer better breathability than solid plastic sheeting.