As a gardener, I can tell you with a certainty that people steal plants. A friend of mine's father had a 40+ year-old staghorn fern stolen from his yard. Gardens and parks are frequently hit by collectors (esp. orchid and tropical plant collectors) and landscapers who are too cheap to buy their own, especially of good stuff that's easy to steal but takes a while to establish, like sago palms and saguaro cactus. It sucks a lot. I'm really sorry.