How many grow games have secret endings

There are three: Grow version 3, Grow Island, and Grow Valley. They have Fire, UFO, and Underground secret endings, respectively.

There is an easter egg in Grow Nano 2, if you do the items out of order, right to left (cape, twig, ribbon), a link to Grow Vanilla appears along with a password (6438) that lets you play a special version of that game.