Questions about greenhouses

Hey everyone just looking for a little help with a few things mainly about greenhouses, I'm planning on constructing one of my own here in the near future and Im just lacking a bit of experience. Iv been familiar with the forums for quite sometime now just havnt really needed to post where Im usally able to find what Im looking for before it gets to that point, anyways I was just curious as to how easy is it to keep a greeny warm throughtout the night. I won't be building nothing to big just large enough to get a good head start on the season by putting 40-50 little ones out where I don't have indoors to work with, it still gets pretty chilly in my region and last frost date is around may 20 if I remember correctly, some things I'd like to know how early can I have some babies out in the cold without them dying, iv did a bit of research on some simple tips on keeping the room warm at night but I'm just not sure what I'll be dealing like how long before they cool down, do I need to heat it during night, what extra steps would some of you recommend for keeping it cosy and what ever else may be good to know,appreciate the feed back and sorry about the long post but figured I'd give a partial introduction with my first post, thanks

Well i know in my greenhouse and Im located in WA state so it still gets cold at night, my babies seem to do fine when it gets frosty out and they are inside the greenhouse. Your greenhouse should retain most if its heat from the day and maybe drop into the 60s at night. But if you wanted to keep it warm I'm sure you could put a little space heater on the floor . That would be fine, but just make sure if its some weird one that burns fuel and not electrical you need to have a place for exhaust but I would far better recommend an electrical one. Otherwise do some research online I'm sure you can find some good ideas. Good Luck!

I should have mentioned I'm actually in eastern Canada last night reached down to minus 10, what kinda things would I been looking at or am I best just to not even bother for a couple weeks guess I'm a bit anxious for the warm weather

Hmmm well you could try the space heater and put a different plant in the greenhouse like a tester plant. And if that plant does ok over night with the heater on introduce one of your MJ plants and then if she does ok Im sure your fine. If not you will prally have to wait a few weeks. Thats the best i can think of.

Ya I was thinking about trying that, I think I got a little electric heater layin around here somewhere, I guess the best way to find out is trial an error I'll try it out here within a couple days hopefully no error hah we'll see though