Dateline: 7 February 2017
The following comment was posted to this site yesterday by Andrew Enjaian...
Herrick, I think this idea has a lot of potential, and I'm eager to see how it unfolds for you this year. My two cents on the plastic:
These are 11mil vinyl: black on one side and a design on the other. I've used white ones for years for animal shelters. The sizes aren't square since they were once billboard signs. Most sizes are 10-16' wide and 20-40' long and they are CHEAP. Right now they have a 20'x60' tarp listed for $108. Most 16' wide sizes are in the $30-50 range. Not sure if vinyl has any strikes against it for garden uses, but I've used the same ones outdoors for years with no problems.
From what I've been able to determine at the BillboardTarps.com web site, billboard vinyl is UV-resistant and safe for plants and fish ponds. I'm not sure about ink used to print on the plastic, but for more money, you can also get new billboard plastic. As Andrew says, the material is very reasonably priced.
I ordered one of the billboard tarps this morning. I'm going to use it over a section of lawn adjacent to my garden. Also, one of my sons wants to make a Minibeds-on-Plastic garden this year and a recycled billboard tarp will make the project a lot more affordable for him.
Billboard "tarps" are much thicker than the bunker cover plastic I now have on my Minibeds-on-Plastic experimental garden.
Thank you, Andrew, for the great idea!