UAF Cooperative Extension Service
Temperature has a direct effect on relative humidity and carbon dioxide levels in the greenhouse. The recommended temperature range for most greenhouse plants is from 50-85 degrees Fahrenheit. Heat can be stored by using dark containers filled with water, or by covering the floor with black woven plastic, so that on cool nights the greenhouse remains in the optimum temperature range. Reflective surfaces, such as white paint, aluminum foil, or reflective mylar, can be used to increase available light to plants.
Ventilation is especially important in the greenhouse environment because it allows air to circulate around the plants. Opening a door for ventilation may be effective for some locations, but ridge and floor vents are recommended. However you configure your system, the idea is to bring fresh air in at a low level, allow it to circulate around your plants, then have a way for the heated air to escape the greenhouse. Low wall or floor vents are important for bringing fresh, cool air in to the plants. Be sure to install screens or other barriers in lower openings to discourage voles from entering your greenhouse. Ridge vents are important for letting overheated air out. If temperatures are still too high in your greenhouse, place a fan by the door to increase available fresh air, or install a fan into a high wall opposite from the floor fan. Simply using a timer for the fan, and manually adjusting the fan speed according to the weather patterns outside can adjust your greenhouse environment accordingly.
Proper ventilation is even more important on cloudy, wet days. Stagnant air can lead to many problems in the greenhouse that can be detrimental to yields. Insufficient ventilation can lead to such problems as dropping of blossoms, lack of fruit set, blossom end rot, and other distressing and costly issues. Some other common ventilation-related diseases in the greenhouse include gray mold and powdery mildew. These problems are encouraged by excess moisture and warm conditions. Avoid watering your greenhouse plants during the heat of the day, and water the roots of the plants. Have a small fan circulating air within your greenhouse if you need to close the door and vents to conserve heat on cooler days.To learn more about gardening in Alaska, contact the Cooperative Extension Service at 895-4215, or stop by our office in the Jarvis Building. Our office hours are 8:30 – 4:30, Monday through Friday. Happy growing!