Actually plants can be mailed. First, you put the plant in a plastic pot with lightweight potting mix. Then you cover the whole pot with plastic wrap. Next, secure it into a box larger than the plant. The best way is to make an insert with styrofoam or cardboard, then tape the pot and insert into the box with packing tape.

I order plants from a handful of nurseries who do a really good job of packing. Another version uses a custom-made plastic lid or clamshell case for the pot and plant, but that's not something that most folks have. Cardboard, foam, tape, etc. are easy to source.

Just in case you ever need to know how to ship a plant, I'm not wheedling.