Frost cloth, often called a floating row cover, is a permeable, lightweight fabric used to protect tender plants against cold temperatures and frost. This material works by trapping the heat naturally radiated from the soil beneath it, creating a warmer microclimate around the foliage. Understanding the proper selection and application of this material is necessary for effectively extending the growing season and safeguarding sensitive plants from unexpected temperature drops.
Selecting the Right Protection Materials
The effectiveness of a frost cloth is directly related to its weight, measured in ounces per square yard. Lighter materials, around 0.5 to 0.6 ounces, provide a few degrees of protection, safeguarding plants from light frost. These fabrics allow 85% to 90% of sunlight to pass through and are often used for insect control and season extension during moderate weather.
For more serious cold events, gardeners should choose a medium to heavy-weight fabric, typically 1.5 to 2.0 ounces per square yard. A medium-weight cloth can offer up to 6 to 8 degrees Fahrenheit of insulation for a moderate freeze event. This denser material reduces light transmission to between 50% and 70%, meaning it should only be used temporarily to avoid hindering photosynthesis. Frost cloth is made from spun polypropylene, which allows water, air, and sunlight to pass through, unlike impermeable materials such as plastic sheeting.
Preparing Plants for Cold Weather
Before applying any protective cover, improving the plant’s natural cold tolerance is important. The most important preparation step is providing a thorough, deep watering in the late afternoon before the expected freeze. Moist soil holds and releases heat more efficiently than dry soil, creating a reservoir of warmth beneath the surface. This retained heat is the energy source the frost cloth will trap around the plants overnight.
Adding a layer of organic mulch around the base of the plant helps to insulate the soil and slow the loss of heat. This layer should not be piled directly against the plant’s stem, but rather spread around the root zone to maintain soil temperature. Clearing away any dead or diseased foliage from the base of the plant ensures the plant is healthy going into the cold period. These measures maximize the plant’s ability to withstand cold exposure.
Step-by-Step Installation Methods
The physical installation of the frost cloth must focus on capturing the heat radiating upward from the soil surface. For low-growing vegetable rows or sturdy, compact plants, the draping method is most appropriate, where the fabric is laid directly over the foliage. This “floating row cover” technique requires the lightweight fabric to extend completely to the ground on all sides of the covered area. It is essential to anchor the edges thoroughly using soil, pins, or heavy objects like rocks or bricks to seal the entire perimeter. Sealing the edges prevents cold air from seeping underneath and ensures the warm air released by the soil remains trapped around the plants.
For larger, more delicate, or taller plants and shrubs, a tenting or framing method is necessary to prevent the fabric from crushing the foliage. This approach involves installing temporary supports, such as metal hoops, flexible PVC piping, or wooden stakes, to create a dome or tunnel structure over the plants. The frost cloth is then draped over this frame, ensuring the material does not make direct contact with the leaves. When covering a frame, the fabric must still be secured at the base of the structure, running all the way down to the ground to maintain the integrity of the warm air pocket.
Timing the Cover and Uncover Process
The timing of application is a determining factor in the cover’s effectiveness and the plant’s survival. Covers should be applied late in the day, ideally before sunset, to trap the heat the soil has absorbed throughout the sunny hours. Applying the cover while the sun is still high prevents the soil from absorbing maximum solar energy for the night. The covering needs to be securely in place before the ambient temperature drops below freezing.
The subsequent removal of the frost cloth is equally important to prevent plant damage. The fabric must be removed the following morning once the temperature has risen above freezing and the immediate threat of frost has passed. Leaving a heavy-weight cover on during a sunny day can cause the temperature underneath to quickly climb, creating a greenhouse effect that can overheat and damage the plants. A general guideline is to remove the blanket when temperatures exceed 50 degrees Fahrenheit, allowing the plants to receive light and air circulation. For multi-night cold snaps, the cover must be removed during the day and reapplied each evening to prevent the stress of prolonged darkness and excessive moisture buildup.