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What Temperature to heat a greenhouse?

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Q: What temperature do I need to maintain in my greenhouse?

A: Temperature depends the type of plants and the desired yield. Some plants just need protection from a hard freeze, others a light frost, and a few tender tropicals don't like temperatures below 60 or 70 degrees F.  In general, I'd set the minimum temperature to 50o F at night.  During the day it should get warmer and you may have to vent a little to keep the greenhouse from over heating.

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Here's a basic outline of plant hardiness, these are the minimum temperatures and not recommended for growing.  Visit Volunteer Park in Seattle for their temperature and humidity settings in their 5 rooms:
 

TYPE OF PLANT

REGION GROWN OUTDOORS

MIN. TEMP

EXAMPLE OF PLANTS

Tropical Plants

Zone 11 & 12: Hawaii

40o F and above

Orchids, Begonias, African Violets, Bromeliads, Heliconia, Some palms, Pineapple, some citrus.

Semitropical

Zone 10: Southern Florida, Southern California,

30o to 40o F

Most Citrus, olive, avocado, mandevilla
banana, passion vine

Subtropical

Zone 9: Inland Texas / California / Areas of the Gulf Coast

20o to 30o F

Ginger, jasmine, passion vine.

Logee's Greenhouses lists minimum temperatures for the plants in Fall 98/Winter 99 catalog.  Greenhouses by Ortho Books has sections on managing your greenhouse and using your greenhouse.  They also have good books on Orchids and Citrus/Subtropical Fruits.

  • Vegetables:  See Sherry's Greenhouse for information on growing tomatoes.
  • Seed propagation: To conserve energy, you will want to purchase or build a seed propagation bed.  It consists of a temperature controlled heating cable set to 70o to 75o and buried in sand.  Build a plastic cover frame that can be opened during the day and recovered at night.  See  Frit's Farm for pictures of their propagation bench.
  • Other considerations: Humidity, Light, Water, and Air Circulation do enhance growth and reduce bacteria, fungi and mold.  I'll try to write an article on this topic soon!  In the interim,  Charley's Greenhouse offers automatic heating, ventilating and humidifying systems.

 

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