Greenhouses extend the season, protecting plants and helping to get an earlier start and keep them going longer.
I have seen pictures of greenhouses made of soda bottles but didn’t include them in the book, 100 Under $100 – but when the book designer laid out the pages, there was a blank page and I was able to sneak them in – really #101, but without any instructions or stories.

Here is a PDF instructable: it is quite a project – we are talking a few thousand bottles. But in most locals, that is an accomplishable goal.

The photo on the left is from an article posted here.