Pst,
Have two tabs open in your browser, one with the Classified forum new thread you are making listing the plants and one for the Daylily Database page.
Go to the database page for the daylily you are listing. Click to open the photo you want to use. At the top where it says "BB Code" copy the code, looks like this
[db_photo] numbers [db_photo]
be sure to include the [ ] on both ends when you copy. Then paste the code into your classified listing. Or you can just copy/paste the web address for that photo.
To link to the database page copy and paste the web address of the database page into your listing.
Daylily (Hemerocallis 'Topguns Code Talker')
You can check how things look with the "preview" button.