greenhouse Miniature Green House Ideas?

With the weather starting to change in Jerusalem, I need to improvise soon. My plants aren't fruiting as fast as I'd hoped. Basically, I'd like to set up some sort of a miniature green house. I didn't measure my balcony, but, I'd say I've got about 3 1/2 ft width X 7 ft length to work with for 10 plants. The temperature right now is okay, with 60s-70s in the day and 50s in the night, but, I know by the middle of next month it might well dip to near freezing in the nights. I'd prefer to avoid exposing my plants to anything like that. Can anyone recommend me something good for a DIY projec to set this up? I think the most crucial element for this kind of thing would be having a heat sink that can warm the space at night. Preferably a non-electric heat sinks.
Thanks in advance!
floricole said:
I think the cheapest heat sink are water barel
Black painted barrels full of water will catch the sun heat during daytime and radiate it back at night.
For the very cloudy/cold days or freezing nights you can use an electric (if possible) or small gas heater.
Good luck
Thermal mass (heat sinks) are a great way to extend the season in a green house.  However, you are describing an area of 3 1/2 feet by 7 foot into which 10 plants must fit.  I do not know that you have room for enough mass.  Certainly not the traditional black painted 55 gallon drum.  You might get a little heat retention from your containers and a bit if the floor is concrete, but I doubt much.  Good news, an electric space heater would probably be very affordable to run in a space like that.  Especially since you will only need it on nights that get cold enough to cause damage. Most come with a built in thermostat that you can fiddle with on a cold night to make sure it comes on at the right temp.

On design, I am a two by four fan.  Slant the top slightly to shed rain water over the side of the balcony.  Being you are not looking for it to last forever, you could use the cheap plastic from a hardware store, duct tape and a staple gun. 

On heating, I would not be surprised if a couple 100 watt light bulbs wouldnt heat a space that small sufficiently.  Just remember to keep the heat source away from the plastic, even the good stuff made for green houses does not like being too close to a heat source.

How hard would it be to enclose the balcony with plastic and open the door on cold nights?
Maybe a few 100 watt bulbs may be a good idea for a heat sink. The main thing is that I'd want to keep my electricity bill pretty low since all the utilities are split equally between 3 other people, they might not take kindly to me running something with such high wattage. A 55 gallon drum sounds cool, but, a bit too cumbersome for my set up and it's very cloudy here in the winter. We have a solar powered water heater and it's painted black, it doesn't get hot in the winter without the boiler. Not sure what the size is, but, it's probably a bit bigger than 55 gallons. I don't think it'd be viable to try and turn my balcony door into a greenhouse extension, either. Primarily because the insulation in my apartment is terrible and there's really no central heat and the gas radiator is shutoff. These older apartments in Israel are built like crap! It's like if they could cut a corner, the corner will be cut. No questions asked.
A gas heater sounds like an idea, but, I'm not familiar with these things. I'm originally from Florida, so, I'd never even seen a heat radiator until I was maybe 22 or 23.
If I understand your goals, you are trying to survive a few cold nights so you can extend the season.  That shouldn't cost much at all because you do not have to heat during the day or on nights that do not dip too low.  I just built a walk in green house, so this coming spring will be the first time I heat something that large.  Previous years, my seedlings went from inside grow room to outside mini green houses long before last frost. 

I used electric heaters that have a built in thermostat of sorts.  It did not have temperature settings, so instead I would decide what temperature I wanted to maintain and watch a thermomiter as the night got cold.  When it got to where I wanted it, I would turn the knob on the heater till it came on.  Then I put it in the mini green house where the air did not blow right onto a plant.  Worked great and only came on when it got cold enough that I worried.  No electric consumption during the day or even during most of the night.  Just that special spot in the AM right before the sun came up.

Now actually heating the thing during the winter, all day long, all night long, now that would get expensive.  But just to extend the season or get a jump start on a new season, not so much.