Protecting plants from environmental extremes, such as cold snaps, intense sun, or invasive pests, is necessary for successful gardening. The correct covering material acts as a barrier, creating a more stable microclimate around the plant. Choosing the right cover depends entirely on the specific threat, whether the goal is to trap heat, filter light, or physically exclude insects. A material suitable for frost protection may be entirely unsuitable for managing summer heat.
Choosing Materials for Frost and Cold Protection
A sudden drop in temperature requires materials designed to insulate and trap radiant heat. Floating row covers, made from spun-bonded polyester or polypropylene, are effective because their non-woven structure allows air and water to permeate while retaining heat. These covers come in various weights; medium-weight options (0.5 to 1.0 oz/yd²) provide 4–6°F of frost protection, while heavyweight versions (1.5 to 2.2 oz/yd²) offer up to 8°F of thermal gain.
For larger plants, shrubs, or temporary coverage, readily available household materials like old sheets, blankets, or towels work well to trap heat radiating from the soil. Natural fiber materials such as burlap are valued for their breathability, which prevents excessive moisture buildup and subsequent freezing on plant surfaces. Burlap’s woven structure insulates plants while blocking damaging winter winds that strip moisture from foliage.
Avoid using plastic sheeting directly on foliage, as it can be counterproductive during a freeze event. Plastic is non-breathable, causing condensation to form on the inside, which can then freeze where it touches the plant tissue, leading to frost burn. If plastic is used, it must be draped over a frame to ensure no contact with the plant, serving as an outer wind and moisture barrier over an inner layer of breathable fabric.
Using Permanent Protective Structures
Structural solutions offer advantages over temporary coverings for extending the growing season or providing long-term shelter. Cold frames are bottomless boxes with clear, hinged lids that function as miniature greenhouses, relying on solar energy to warm the interior. They are used for hardening off seedlings in spring or growing cool-season crops late into the fall or winter.
Cloches are smaller, often bell-shaped or tent-like structures made from glass or rigid plastic, designed to cover individual plants or short rows. While original cloches were bell jars, modern versions include clear plastic tunnels. These structures protect against wind and cold while trapping solar heat. They require manual venting on sunny days to prevent overheating.
Hotbeds are a variation of the cold frame, incorporating a heat source beneath the soil (historically manure, now often electric heating cables). This addition elevates the soil and air temperature considerably higher than a standard cold frame. This enables the propagation of warm-season crops much earlier in the spring.
Materials for Pest and Sun Screening
When the concern is insect damage or intense summer sunlight, materials shift from insulating fabrics to specialized barriers. Fine mesh netting is the most effective way to exclude insect pests without relying on chemical treatments. The mesh size determines exclusion; common netting features holes around 0.8 to 1.4 mm, sufficient to block larger pests like cabbage root fly, carrot fly, and cabbage white butterflies.
For micro-pests like whiteflies, aphids, or thrips, an extra-fine mesh with pore sizes as small as 0.27 mm by 0.77 mm may be necessary. These insect screens create a physical barrier while permitting high light transmission (often 80–90%) and allowing air and water to pass through.
Shade cloth filters sunlight to mitigate damage from intense heat and UV radiation. These materials are rated by percentage, indicating the proportion of light they block. A 30% shade cloth is suitable for light-loving crops like tomatoes in hot climates. A 50% shade cloth balances protection for leafy greens and general greenhouse cooling. Higher percentages, such as 70%, are reserved for sensitive plants like ferns or orchids.
Installation Techniques and Timing
Successful protection relies on proper installation of the chosen covering material. When using flexible materials like floating row covers or old blankets, the cover must extend all the way to the ground to effectively trap heat radiating from the soil. The edges must be firmly anchored to prevent cold air from entering underneath and to keep the cover from blowing away:
- Soil
- Rocks
- Bricks
- Specialized fabric pins
For all cover types, use hoops, stakes, or a simple frame to support the material and keep it from resting directly on the foliage. This air gap provides the insulating layer for frost protection and prevents physical damage. When applying covers for frost, action must be taken in the late afternoon or early evening before temperatures drop significantly, to trap the residual warmth accumulated in the soil.
Ventilation management is necessary once the threat has passed. Covers should be removed promptly the following morning, typically by mid-day, once the temperature rises above freezing. This prevents the buildup of excessive heat and humidity, which can cause plants to overheat, stress, or develop fungal diseases. While many covers are water-permeable, prolonged coverage requires careful monitoring of soil moisture.