mikevan

It can be as short as you want it to be. 9' wide and 6' tall and 52" long hoops placed end to end. You can put a couple of cattle-panels together to form a 9x9' greenhouse, basically.

I used the basic grey metal 1500 watt utility heater you find at any hardware store. I didn't try to keep it warm in there - just acceptably above freezing. I also grouped my plants and kept them warm rather than tried to make the whole interior warm. Smaller greenhouse and dual covering means more efficient heating capability. Beware tho - and this goes for any greenhouse - when the sun comes out, it heats up *FAST*! Without venting, it can easily get to 120F in minutes! My vents were on the ends. I just folded the plastic back. This time around I'll be a little more sophisticated and use hinged vents on the plywood ends. Two sheets of plywood side-by-side covers the end - with the trimmings placed beside them to make up the extra foot of difference. Then you can cut a door and vents and hinge them and either operate the vents manually or install those greenhouse vent openers. Put vents on either side. One low and one high also works well - cold air coming in thru the low and hot air rising thru the high would help keep a constant flow. An exhaust fan would help too on windless days. At night, close it up and set your heater to freeze-guard and be happy. I have a wireless thermometer so I can monitor the temps at any given moment plus track high and low temps too. Put your containers close together. You can even pour sand between them as well to limit a draft amongst the pots and chilling the roots. The poly will rain - get ready for wet hair when you're in there. A double-layer won't have so much of a problem. Put an umbrella above your heater too.

And being out there in the rain is an adventure! The sound is deafening!

Have fun,
Mike