Building planter from scrap lumber

Hi,

I'm building a couple of wooden planters from scrap lumber.  The
lumber is pressure treated, but that's all I know about it.  I will be
growing vegetables in the planters, so I am wondering what I should do
to treat the lumber.  Should I do anything to the interior surfaces?
I'm guessing that stain or paint is not a good idea if I'm going to
eat the vegetables grown in the planter.

Thanks for the advice.