5 gallon water jug mini green house question?

I was reading in my MARIJUANA HORTICULTURE THE INDOOR/OUTDOOR MEDICAL GROWERS BIBLE and I noticed you can extend your growing season by using cloche, which is basically a one gallon plastic milk container you cut the bottom out of and put over plants leaving the cap off to protect against freeze to start you crop early to have a spring harvest. But my question is if you used a five gallon water jug and cut the bottom out and did the same thing as the milk container would it work like a individual green house so that i could start like in the next couple of weeks. I live in southern Cali so its relatively pretty warm most of the time rarely below 50 F in the winter at night. Heres a picture of what im talking about

Just wish my plants were as big as that picture!!!

Whoa big picture. It would make sense though. The plant would grow out of the top of the jug and the roots would be protected somewhat in the container, while still having the ability to grow out and into the outer soil.

Ain't got no problems with frost here so can't help ya there.