Via New World Geek, plans for a greenhouse that you can make from 1,500 plastic two liter soda bottles! [pdf] The plans are geared towards kids, as a class or community project.  The soda bottle greenhouse is published by REAP, a "local sustainable development charity" based in Scotland.

Here is what I love about this project: it upcycles consumer waste.  Typically these bottles would be recycled (if you are fortunate enough to live in an area which accepts PET #1 plastics for recycling).  Although PET plastic recycles better than other plastics, the PET recycling process still leaves a lot to be desired.  Unlike substances such as glass, which can simply be melted and poured back into shape, PET plastic recycling is a far more involved process.

First, the plastics have to be sorted by color (transparent, green, and "other").  Next they are shredded into tiny bits, labels and all.  These flakes are then sorted into pure PET plastic flakes and "other," with the "other" parts (labels, caps, etc) being thrown away.  At some point in this process (depending on the recycler's procedures) the PET plastic has to be cleaned.  With - you guessed it - some pretty nasty chemicals.

And of course, just because you drop something in the recycle bin, that doesn't mean that someone else wants to recycle it.  Several recycling programs are suffering from a supply and demand problem - people are recycling more glass and plastic than the recyclers want to buy.  The problem is that there often isn't enough upstream demand from companies that want to use recycled PET plastic.  And this tends to be a highly localized issue, because shipping bales of recycled plastic to the next state or time zone is economically problematic.

Upcycling - just re-using the item instead of breaking it down and re-forming it - is clearly the best option.  But there just aren't very many options for upcycling plastic soda and water bottles.  According to Wikipedia, clear plastic bottles can be used for solar water disinfection, since plastic lets UV rays through, while glass does not.  I found a lot of kids' crafts that use plastic bottles, but I have the feeling there are only so many two liter penguins a family can make.

And so we circle back to the recycled bottle greenhouse!  This project uses 1,500 plastic two liter bottles, so each greenhouse sequesters a formidable amount of bottles from the overloaded recycling stream.  I think it would work really well as a greenhouse, since the airspace inside each column of bottles will act as an insulation barrier.  It's a great project for a school, a family, or a community garden.  And I don't know if you've priced out the cost of a new greenhouse recently, but they are really expensive!  A conventional greenhouse is also made of lots of new plastic, of course, which means that it carries a positive carbon footprint.  Whereas a greenhouse made from PET bottles would carry a negative carbon footprint, since you're saving the ecological cost of the transportation and machinery required to recycle it.

Start saving your bottles today!