Do Plastic-Covered Plants in Winter Need to Breathe?

Basics of Plastic Row Covers

• Plastic coverings for garden plants are commonly known as row covers. These usually consist of a clear plastic that covers some kind of PVC or wire framework. Different thicknesses of plastics provide different insulation values. These plastic covers are most effective when water condenses inside the tunnel. The condensed water and humid air help keep the ambient temperatures warmer in the evenings. Research performed by the University of California Division of Agricultural indicates that air temperatures can be increased by 6 to 20 degrees Fahrenheit, and soil temperatures can be 4 to 8 degrees warmer than outside soil temperatures. In the winter, soil temperatures are crucial to the life of the roots of plants.

Potential Benefits

• Besides warmer soil temperatures, row covers can protect plants from frost, wind and pests. Plastic row covers can extend the growing season of a plant and protect seedlings, giving them an early start towards maturation in the spring.

Potential Damage

• Row covers can create too hot of an environment for the plants. Warm temperatures and direct sunlight will cause the temperature under plastic to increase dramatically and could injure the plants. The humid environment is what keeps the plant warm, but humidity can encourage the development of disease and mold. Covers can also become a shelter for insects and small animals.

Putting it All Together

• When considering when to ventilate plants under row cover, weigh out the advantages and disadvantages. If temperature are reaching above 50 degrees Fahrenheit, it is best to provide some ventilation. The plants do not have to be completely uncovered. Opening the tunnels at the ends may provide enough airflow and help keep some moisture in the tunnel. Try to ventilate during the warmest part of the day and close everything up while the sun is still out but temperatures are cooling. This will trap some of the day's warmth inside the tunnel. If you find mold or rot, try to uncover the plants during a warm period and clean off any diseased plant material. If pests or animals are becoming prevalent, then exposing the plants may help. Traps can also be used for small rodents trying to make a home under the plastic canopy.