Not sure this is the right spot, What is the best temperature for my greenhouse?

Christopher Ford

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I just built a small greenhouse on my back porch and it is already getting hot in there. I have a auto vent and am waiting for a temp gauge to arrive. What would be a good average temperature to aim for? I want to grow herbs, lettuce and then seedlings.
 

ClissAT

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Hi Christopher, it's got more to do with humidity than plain straight out temperature.
Many spring summer plants will happily grow in 100degrees but not 100+99% humidity.
The humidity must be allowed to dissipate so the plants don't boil.
Have a look at commercial growing sites online for your area or ask your local extension officer.
 

Phillip Pavis

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Thisbte of year soil temps are key. Seeds sprout in warm soil. They can grown in colder soils. Which is why we sprout indoors then transfer to the greenhouse that we keep above 40°f
 

cwinds

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I just built a small greenhouse on my back porch and it is already getting hot in there. I have a auto vent and am waiting for a temp gauge to arrive. What would be a good average temperature to aim for? I want to grow herbs, lettuce and then seedlings.
It would be tricky to grow lettuce in the same greenhouse as herbs & seedlings. Lettuce is a cool weather crop, but herbs & seedlings like it warm. I would aim for 80-85F for the herbs & seedlings, then maybe try to keep your lettuce shaded and/or in the coolest spot you have. It's still likely to bolt fairly quickly at that temperature, though.
 

daveb

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as you can see its not just temperature its got to take into account what are you growing , daytime temps and humidity - night temps and humidity and day night cycle. as for lettuce day time in my hydroponics i shoot for 60 to 70 max range daytime and 55 to 65 night time, get above 70 for to long and your lettuces can get bitter take on off characters in flavors and bolt, and as for humidity you need to play it by ear i keep my hydroponics area in the 45 to 55% range depending on air movement , which is another thing you will need to make sure to have in green house a small fan to keep air passing over plants so the air boundary at leaf layer doesn't go stagnant, mother nature does this natural in light breeze and air movements as it warms and cools during day outdoors. germination needs to be higher 60 to 85 degree but i would suggest try to keep it below 80 for most seeds. the other factor to take into account is are you supplementing with any additional light early growth and increased root growth takes advantage of extra blue spectrum lights during early growth until first couple sets of true leafs grow.

as for herbs add 5 to 10 degree for growing temps of lettuce depending on the variety of herb and the region they originate from. basils and a number of other will do ok in same relative range as the lettuces tho, others plants like peppers tomatoes like warmer temperatures these are max daytime/ min night temperatures you can use the same idea for lettuce just drop about 8 to 10 degrees, cabbage and other cold crops treat like lettuce and maybe a few degrees cooler
tomatoes/peppers DAY/night
Germination 78oF 78oF
Seedlings 78oF 62of
Mature Plants 78oF 64oF

edit added .... one thing i did forget to mention if you are supplementing with grow lights that have a tune-able light spectrum you will want to adjust accordingly, if you are growing for seedlings to plant later stay pretty much balanced red to blue at 1:1 or 2:1 ratios. if you grow indoors in green house year round dont forget to adjust for tomatoes and peppers and other fruit bearing and blooming plant i use 2:1 and 3:1 with tomatoes and had ok growth and fruit but as much as 5:1 red/blue and seen remarkable jump in production
i attached a guide for germination but personally some of these temperatures they state are too high because most people tend to over water when germinating seeds and over water at some of theses temps and you will get a fuzz ball of mold where seed was
 

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