“The toilet paper tube thing is to fill the tubes with soil, tie them together so they stand up, plant one carrot in each tube, and then when it’s transplant time,just put the whole tube in the ground with the green top exposed.”
I could do that, have plenty of the tubes, prepare them and put under grow lamp, then when they are ready, plant the whole thing. That should work. A half tube would work. I have read how to secure the end of a tube so can do that.
I just put the tubes in a short wide pot to keep them standing up. Unfortunately, I had trouble getting the seed to germinate that year, so didn’t really have a great test of the concept.