If you want to have some of your Plant List private, you can now do so. It is a category based system and it works like this:
Create a new (or edit an existing) a category. Under "Privacy settings" you can choose to make it open or private.
If you choose private, then only you will be able to see that category and anything under it. You can test this by creating such a category, populate that category with plant entries along with your notes. Then logout and go view your list as a visitor and the items in your private category shouldn't show up at all.