When you click "add a plant" in the Plants Database, you should get a screen that looks like this:
http://garden.org/plants/add.p...
Then, for this particular case, just type:
"Tall Bearded Iris" (without the quote marks) in the Plant's primary common name box
"Iris" (without the quotes) in the Genus box
and "Amanda Erin" (again, no quotes) in the Cultivar box
Click "Add The Plant" and you should get a message saying that it will be reviewed by the moderator (Polly or Dee for irises). Once they approve it, you can add pictures and other information. Hope this helps.