Treenway Montano Silk Cord in Cedar, one strand for each stem and a long straight stitch. I used a solid 7mm white ribbon (from my stash) for Lazy Daisy Stitch iris tops, or "standards" (the technical term). Then Treenway Silks 7mm Montano Silk Ribbon in Daffodil, lovely variations of cream to a deep yellow, for the "Falls" in the Japanese Ribbon Stitch. Last but not least, some 2mm pale yellow ribbon again from my stash for a straight stitch "Beard" on each "Fall" (which you can see in the last photo).
Then I added straight stitch leaves in 3.5mm Treenway Montano in Spring Green. To add dimension I twisted a few of the leaves and positioned them lower and at different places to make the iris look taller and more realistic.
Next will be a "tree" next to the wall using twisted bunches of thread to assimilate the bark with leaves on the branches.