Greenhouse Conditions
Air and Soil Temperatures

Carbon Dioxide: A Breath of Life Carbon dioxide (CO2) is essential to the process of photosynthesis. If it's scarce, plant growth slows. If your greenhouse air is stagnant, plants can deplete the carbon dioxide in the layer of air surrounding the leaves, even though there may be plenty in the rest of the greenhouse. Keeping the air moving, via vents or fans, is important for providing necessary CO2 to plants. Some home and school greenhouse growers have tried increasing CO2 by composting right in the greenhouse, since the composting process produces carbon dioxide as well as heat. Consider challenging your students to invent other ways of providing CO2 (e.g., human breath or dry ice!) and experiment to examine its effects on plant growth.

Air - Plant growth requires heat. Temperature determines how quickly plants take up water and nutrients, their rate of photosynthesis, and their growth. Maintaining a comfortable air temperature for your plants can be a challenge. Generally, 50 to 60°F is a minimum temperature for greenhouse plants, while 85°F is the maximum. Plants generally do best with a 10- to 15-degree drop between day and night temperatures.

Tropical natives or food plants that produce edible fruits (e.g., tomatoes) can probably withstand higher temperatures. Plants native to more temperate climates, or those with edible leaves or roots (e.g., lettuce), typically prefer cooler temperatures.

Soil - Soil temperature is even more important than air temperature in your greenhouse, particularly if you're growing in beds. When soil temperatures are below 45°F, roots grow more slowly and are less efficient at taking up water and nutrients. Warm soil is particularly important for germinating seeds or rooting cuttings.

Sixty-five to 75°F is recommended for germinating most types of seeds. Have students use a special soil thermometer to monitor soil temperatures, and consider experimenting with growth rates of seedlings in warmed and unwarmed soils. You can supply bottom heat for containers by purchasing special soil heating cables or mats. Be sure to read the safety precautions carefully, and never try to adapt an electric blanket or heating pad for greenhouse use!

 

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