How to Protect Greenhouse Plants From Frost

Written by abe whitmar
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Nothing takes away winter's bite like a table adorned with fresh cut flowers and brimming with produce fresh from a nearby greenhouse. With a little preparation, growers in even the coldest climates can protect greenhouse plants from frost and enjoy harvests year-round.

An insulated, airtight greenhouse, protected from the wind, located for maximum solar exposure and filled with material to hold heat, can protect plants from frost in many regions. Where a well-built greenhouse can't prevent frost, partitions or plant covers can isolate fragile growth, and a heater can keep temperatures above the freezing mark so plants can thrive in even the coldest climates.

Skill level:
Moderately Challenging

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Things you need

  • Thermometer
  • Insulation
  • Thermal mass (soil, water, rocks, etc.)
  • Heater (optional)
  • Fan (optional)

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  1. 1

    Plan as early as possible to protect plants from frost. Know your area's climate. When designing and siting a new greenhouse, look for locations away from prevailing winds and protected by other buildings, trees or terrain. Orient the roof and walls to increase exposure to the sun. In an existing greenhouse, study greenhouse temperatures as winter approaches. Monitor weather forecasts for impending frost conditions.

  2. 2

    Close any gaps or openings that let air into or out of the greenhouse. Control ventilation to keep temperatures even during the high and low extremes. In a glass greenhouse, inspect caulking, and weatherproof operable windows. Use tape or caulk to close openings in plastic or fibreglass structures.

  3. 3

    Monitor greenhouse temperatures at different times during the day and night. Learn when are the coldest times of day, what locations in the greenhouse offer warmer temperatures, and where temperatures drop the most. Standard outdoor thermometers can be manually read and recorded. High-low thermometers provide a more complete record. Automated recording systems, frost alarms and thermostatically controlled heaters can make it easier to monitor greenhouse temperatures.

  4. 4

    Insulate your greenhouse according to the requirements of your climate and your growing plans. A cool greenhouse can protect plants from frost but warmer temperatures are required for year-round growing. Insulate with storm windows or an additional layer of plastic or fibreglass.

  5. 5

    Isolate plants from frost-prone areas of the greenhouse. Greenhouse temperatures are usually warmer away from the floor. Put plants on tables in raised planters. Make row covers or fit individual plants with covers to keep frost at bay. Protect greenhouse plants from frost with blankets draped over them if no other cover is available.

  6. 6

    Store heat from the sun or from heaters by keeping your greenhouse full. Soil in plant containers stores heat. Bare earth, stone, concrete or tile floors also store heat. Large closed containers of water can store enough heat to keep protect plants from frost in many regions.

  7. 7

    Use a heater to protect plants from frost on the coldest winter nights. Locate the heater to provide even temperatures around plants. Use a fan to circulate warm air. Limit excess energy use with a thermostat. A heat-intense lighting source can extend daytime warmth and protect against early morning frost.

Tips and warnings

  • Watch for fire hazards associated with use of heaters.

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