I just read one of those handy little hints that show up on the internet, and I think that it is an interesting idea, and one that many of us can use. The basic idea is to take the empty toilet paper roll, cut 3-4 slits in the bottom, and fold them inward, making a base at the bottom of the tube. Then , you get a container (bowl, pan) of potting soil, dip the TP tube in that and fill it with potting soil. As you get the tubes filled, you put them in a container that has high enough sides to hold the tubes upright. Rolls from paper towels can be cut down and used for this purpose also. Once you have all of the tubes filled and standing upright in the conainer, then plant a seed in each one. When the seedlings are ready to plant outside; you simply plant it right inside the cardboard tube, and that will soon disintegrate as you water the plants, and the roots will find their way out and into the dirt.
That is a good use of something that was going to be thrown in the trash. I am a gardener, I save all can of things to use as containers for my seedlings for my new garden. I also use milk containers as planters.
I've never tried that but it's a pretty good idea. My DIY pots are made by cutting the tops of juice bottles and then making some drainage holes in the bottom. I like to do that when I propagate new plants from cuttings because the transparent pots make it easy for me to see when my cutting start growing roots. Of course with seeds that's not necessary because once a seeding pops its head out of the ground, you can be sure that it's developing roots too.