Worm Towers in the Mandala Garden

My question, as a worm composter in the winter, has always been "How do I use the worms in my garden?" because I don't want to do as much worm composting inside (I keep a bin going just so I don't have to buy more worms for the cold winter, when the compost pile seems so far away). Building these worm towers was an answer that intrigued me. The idea is that one can put the worms into the tower, place food into them (worm-type food: straw, manure, kitchen scraps and a splash of water now and then...) and let their tunneling create oxygen to the roots of the plants, and pockets where the water can seep in, and leave behind their black/gold poop as fertilizer. 

The theory is (of course I had no view into their wormy world) that they will eat, travel out the holes and into the surrounding growing area, and back to eat again. 

Some considerations: 

1) There is some talk out there (here's me not trusting the interwebs completely) that the worms will eat the feeder roots of plants. After a very successful season despite our rainy weather, I would say that my findings are that they don't. But do some research. I'm open to hearing from experts on the matter.

2) The worms die in our zone 3 climate. At least this is what I've been told by my worm gurus. I'm hearing from a couple sources that they are mutating in our climate and surviving our winters. Which brings us to...

3)Is it ethical to introduce a new species to our climate? (obviously, I went ahead with reckless abandon)

Here's some how-to:

WWOOFer, Ryouta cut this 6"pvc pipe that we had kicking around (in the barn for too long) into 3' lengths on the chop saw and then drilled 1" holes into the bottom 1 1/2' of it. If I had it to do it again, I would only drill 1' up from the bottom so there's less to bury.

 One buried worm tower wit ha tomato cage around it. I have no pictures of the 100 tomato plants I planted, roughly 40 of them on worm towers. I had one on either side of each tower. Next year I shall also plant 2/ tower, but a quarter turn around the tower, because I left the roots in the ground. I hope that these will decompose by the following year so that I can plant in the original spots again.

 Here are two of the worm towers, buried in the Mandala Garden.

A lovely picture of the Mandala garden in it's prime (see the worm towers poking up?) , the flood (about 1/2 receded at this time), and the new sand stone rock steps leading down to the new patio, which also acts as a heat sink for some potted tomatoes and basil.... more on that soon.