Protecting plants from sudden drops in temperature, frost, or harsh winter conditions is essential for gardeners looking to extend their growing season or safeguard vulnerable species. When temperatures fall, covering plants is a highly effective method of insulation, trapping the natural warmth radiating from the soil. Successfully mitigating cold damage requires a methodical approach, starting with selecting the right material. This strategy ensures that tender foliage and developing buds survive unexpected cold snaps.
Choosing Appropriate Plant Cover Materials
The choice of material directly affects the level of protection a plant receives, based on the material’s insulating and breathable properties. Floating row covers, often made from spun-bonded polypropylene or polyester, are a widely used option because they are lightweight and allow both light and water to pass through to the plants. These fabrics are graded by weight, with medium-weight covers offering a temperature increase of approximately 4 to 6 degrees Fahrenheit and heavier grades, like Agribon AG-50 or AG-70, potentially protecting down to 24°F. Breathable fabrics prevent moisture buildup, which can freeze and cause damage, and they do not generally require removal during the day unless temperatures rise significantly.
Heavier materials, such as old blankets, burlap, or cotton sheets, offer superior insulation by trapping more heat. However, they must be kept dry because wet fabric promotes cold transfer through evaporative cooling. These dense, opaque materials block sunlight and airflow, so they are not suitable for prolonged coverage and must be removed promptly each morning. Plastic sheeting is the least recommended option for direct contact, as it is non-breathable and transfers cold directly to foliage. If plastic is used, it must be clear, heavy-duty, and suspended over a frame to maintain an air gap around the plant.
Proper Installation and Support Methods
Effective plant protection relies on creating a thermal barrier that traps ground heat without allowing the cover to rest directly on the plant tissue. A rigid support structure must be constructed using flexible PVC piping bent into hoops, sturdy wooden stakes, or wire cages placed around the plant. The support structure ensures that a protective air pocket is maintained between the foliage and the covering material. This prevents cold transfer that occurs when frozen material touches leaves, which can result in localized damage.
Once the support frame is in place, the chosen material should be draped over it, ensuring the cover extends fully to the ground on all sides. Sealing the cover at the base is necessary because the primary source of warmth is the heat radiating upward from the soil, which must be trapped underneath the barrier. The perimeter can be secured by heaping soil over the edges, placing heavy stones or bricks along the base, or using landscape staples. Additional anchoring is necessary in windy conditions to prevent the cover from being lifted or blown away, which would expose the plants.
For taller shrubs or trees, the material should be wrapped loosely but completely around the canopy and tied gently at the trunk, ensuring the bottom edge is secured to the soil. The goal is to create a fully enclosed, temporary microclimate where the temperature remains elevated compared to the outside air. The covering should be taut enough to shed rain or light snow but loose enough to avoid damaging branches or compressing the foliage.
Understanding When to Cover and Uncover
Timing is significant for successful frost protection. Gardeners should monitor weather forecasts and prepare to cover plants when temperatures are predicted to drop into the mid-30s Fahrenheit, as frost can form even above 32°F. Covers must be applied before sunset, which is when the ground begins to lose the heat it absorbed during the day. Applying covers at this time traps that residual warmth underneath the barrier for the night.
While covers provide short-term protection, leaving them on too long poses a risk of plant damage due to excessive heat and moisture. Once the air temperature rises above freezing and the sun is fully out the following morning, the cover must be removed or vented immediately. Failure to remove opaque or non-breathable covers can quickly cause the air temperature inside the enclosure to soar, leading to overheating and scorching of the foliage. Trapped moisture under the cover also creates a humid environment that encourages fungal diseases.