>> so lightweight that the wind easily blows them around. Even with soil and plants in them, they are knocked over.
I agree. The 2 liter bottles are tall compared to their width and tippy if they aren't packed together in something like a box.
A concrete coating and a wider, flat base would make them much more stable.
I've thought about giving away seedlings in paper cups so they would HAVE to plant it out or pot it up before the cup falls apart. But that's kind of a mixed gift!
Giving them a good-looking pot is much kinder.
