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What is the Correct Greenhouse Temperature Range?

What is the correct temperature range?

Greener Thumb
Posts: 1868
Joined: Tue May 25, 2004 10:44 pm
Location: Maryland zone 7

Hi Kimberly,

It depends on what you are growing. From Orchidguy at GW:
As with anything in life, these are only averages. My plants never read the book!

Temperatures variances far outside these ranges can cause slower growth, flower drop and other problems.

Higher temperature greenhouse: tropicals, plants grown for their fruit (tomatoes, citrus, etc.) 60-85 degrees F.

Moderate to cool temperature greenhouse: houseplants, plants grown for their leaves or roots (cool season veggies), overwintering plants, maintaining shrubs, cool weather vegetables.
45-75 degrees F.

All greenhouses have 'micro climates', areas that are warmer or cooler than the thermostat says. These can be around windows, along the west wall in summer, etc. You can use these areas to your advantage, watch out for them!

In the real world, summer temperatures will exceed the optimum growing temps, for any type of greenhouse unless you have a very tightly controlled environment. Southern areas of the US may have problems controlling temperatures unless cooling systems are installed. Northern areas of the US may have the opposite.

Super Green Thumb
Posts: 4659
Joined: Thu Oct 21, 2004 5:58 pm
Location: Victoria, BC

Greenhouses (or cold frames) go through a wide variety of temperature ranges. In winter they can go as low as the ambient temperature outside. Often people use heating cables to protect plants inside their cold frames from the cold.

Greenhouses do protect plants from the elements though.

On the other end of the spectrum; temperatures in a greenhouse during summer can go well up into the hundreds.

Here is a tip: Place a large container (garbage can, old oil drum, etc.) inside your greenhouse and fill it with water. Water has a high specific heat (amount of energy needed to raise the temperature by one degree) and will absorb excess heat keeping the temperature down in the summer. The high specific heat of water will also allow it to hold onto the heat in winter and keep your greenhouse a few degrees warmer in the winter.

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