TY so much for the tips! That joggled a memory about the lady at the PO saying something about priority instead of flat rate boxes a while back. They are the same size, right? They are so handy because everyone knows how big they are, what to expect. Except for a few things like elephant ear bulbs, plants are very lightweight.
If my excess plants can help get new tires on my car, while the recipients find plants they would like to have, that's my goal in doing this. DH has been riding his bike to work and I've kind of taken over his truck since I work abut 15 miles away. I'm not trying to start a permanent side-business, just trying to soften the blow of a fairly large expense.