I love this idea, I know people in Europe do this, Norway, Sweden and here in the US. I hope to do this myself for my trees here in Nebraska - it gets very cold. I was driving to the library and a house in a nearby neighbor had her tree knotted. The calendar is for autism.
If you go to Flickr you will see lots of photos from Knotty Knitters.
Start knitting, you can use up those small balls of yarn.