These grow in water, along the edges of ponds, in bogs, I have them in my swale garden.
They can be invasive use appropriate cautions. Do not plant them unless you are sure you want them. They are extremely difficult to remove once established.
They are used in sewage treatment to remove metals from waste waters.
They grow in full sun and part shade with no trouble here. If it is wet, they will grow.
They bloom prolifically early-mid March and are just now winding down the middle of April.
The Houston summers do not bother them, the cold winter of 2009/2010 caused a little bit of die back, but most of them pulled through just fine.
Yellow flag iris can be found wild in bogs from Scandinavia to Siberia and as far south as North Africa. Clovis I, King of the Franks made it his family flower. On a campaign from Germany they found their way through the swamp by following the flag irises. Since they will not grow in deep water, he knew the swamps would be shallow enough to march his army through where ever they found this flower.
These are doing just fine despite more than 3 months of no rain and 100’F plus temperatures.