I did something simular. I planted tomatoes early, surrounding each plant with 3 filled pop bottles and covering all with plastic.

These plants did just as well as the ones in wall-o-waters. But, the WOW's are more attractive to the eye and easier to handle than plastic drop cloth, so I basically stick to them.

Kay.

What's the purpose of the teabag?

Yeah....what is the purpose of the tea bag? To make the water dark so it takes in more heat? Maybe the acid keeps it from getting green and gross inside?

Kay.

When I had gardening space I used large clear green drink bottles and compared to WOW. I preferred the bottles. I put six bottles around each plant providing more heat than WOW as determined by a recording thermometer which I got cheap from a nearby popular consumer electronics outlet.

It makes sense. The water in the pop bottles holding heat longer. You had a lot more water in them than the walls.

I used inverted 2 liter soda bottles a couple of years ago to supplement watering. I left the lids on with a couple of small holes poked through them. Obviously, the bottom of the bottle was cut off to allow for filling. These would drain themsleves in a day or so.My eggplants loved them! I suppose one could surround a plant with these if the outlet holes were small enough to prevent overwatering, thus watering the plant and keeping it warm too.

No answer on the teabag? As I read the original post I thought it was a great job of muli-tasking by making sun tea at teh same time. In the morning, when it is coolest, dump the tea into a pitcher for the fridge, and refill bottle for garden so it has time to warm up during the day.

I'm sure that's not it, but I'm now considering it.

Ken