A frost cloth is a specialized protective fabric used by gardeners and growers to shield vulnerable plants from freezing temperatures and unexpected frost events. The primary purpose of this material is to create a warmer microclimate around the foliage, extending the growing season into colder periods of the year. The cloth offers a reliable defense, protecting tender vegetables, flowers, and small trees.
What Defines a True Frost Cloth
A true frost cloth is a spun-bonded synthetic fabric, most commonly made from polypropylene or polyester, engineered specifically for horticultural use. The non-woven fibers are lightweight, allowing the cloth to be draped directly over plants without causing damage. Crucially, the fabric is breathable, permitting air exchange and preventing the buildup of condensation or excessive heat. Unlike solid materials, a proper frost cloth allows both light and water to penetrate, meaning plants can continue to receive moisture and energy even while covered.
How Frost Cloths Protect Plants from Cold
Frost cloths work by altering the immediate environment surrounding the plant, primarily by managing heat loss. During the day, the soil absorbs solar energy, which is then released as long-wave radiant heat at night. The cloth acts as an effective barrier, trapping this rising heat within the covered area, similar to a mini-greenhouse effect. The cloth also provides a physical shield against wind and radiational cooling. It slows air movement, reducing convective heat loss, and prevents the direct formation of ice crystals by blocking the plant’s exposure to the cold night sky.
Selecting the Right Weight for Protection
Frost cloths are categorized by their weight, typically measured in ounces per square yard (oz/sq yd), which correlates to their density, light transmission, and level of cold protection.
Lightweight Cloth
Lightweight fabric (around 0.5 oz/sq yd) allows maximum light transmission (85% or more) and is suited for light frost or insect control, offering two to four degrees of protection.
Medium-Weight Cloth
Medium-weight cloth (0.9 to 1.25 oz/sq yd) is a versatile option for moderate freezes, providing four to eight degrees of protection while allowing 70% or more of sunlight to pass through.
Heavy Grades
The heaviest grades, known as thermal blankets, weigh 1.5 oz/sq yd or more and are designed for hard freezes, offering up to 10 degrees of thermal protection. This increased density significantly reduces light transmission, sometimes blocking 50% or more of the sunlight. Heavier grades should generally only be used for short, severe cold snaps.
Proper Installation and Usage Techniques
Effective protection depends on correct installation, which must focus on trapping the maximum amount of ground heat. The cloth should be draped completely over the plant or row, ensuring the fabric extends all the way to the ground on all sides. Securing the edges with heavy objects, such as rocks, bricks, or garden staples, is necessary to seal the cover and prevent warm air from escaping. If the cloth is simply tied around the plant trunk, the heat radiating from the soil is lost, significantly reducing the protective effect.
For optimal insulation, especially when expecting a hard freeze, creating a tented structure or using hoops can be beneficial. Keeping the fabric off the foliage prevents cold transfer if the cloth becomes damp and provides a layer of insulating air. The cloth should be applied before sunset to capture the day’s warmth and must be removed once temperatures rise above 40 to 50 degrees Fahrenheit.