Plant it for the flowers; love it for the foliage, texture and vertical punctuation!
Native iris are easy to grow. There are two types, tall and short. Both grow just fine in medium and moist soils. The shorter iris is also drought tolerant once established. The taller iris can also grow directly in as much as a couple of inches of standing water. Both have gorgeous blue to violet flowers.
Most significantly, for design purposes, both have very vertical foliage that stays upright through the growing season and easily provides the textural contrast with other leaf shapes garden designers are always advising us to add to our gardens to make them more pleasing to the eye.
Tall ornamental variegated iris in professional designer Barbara Katz' garden proves the point beautifully. Imagine this photo without the iris. This waterfall view would still be enchanting. With the iris though, the scene zings!
Whether planted with maidenhair fern, bunchberry dogwood or Christmas fern in a container, dwarf crested iris, though short, also creates contrast!
What to Know to Grow
Northern Blue Flag Iris (Iris versicolor)
Tall northern blue flag iris grows in sun or part shade in medium to moist to wet soils. It forms clumps that reach 2 to 3 feet in height and about the same in width. It grows by rhizomes but spreads slowly. It blooms a little later than the shorter iris, in May to June. The Missouri Botanical Garden advises wearing gloves should you divide it. In our garden, it grows in part shade and, as a result, gets only a few blooms per clump. For maximum bloom, it seems to need full sun.
There is some variety in the colors of the flowers. An increasingly popular cultivar of blue flag called "Purple Flame Blue Flag" (Iris versicolor 'Purple Flame') developed by Mt. Cuba is available at many garden centers and native plant nurseries. It has the same attributes of the blue flag including the flower except the base of the sword like leaves emerge a purplish blue in spring and hold the hue until the plant fully develops for the year. To highlight this feature, it's helpful to grow the plant in full sun and in a location with no other plants in front so you can appreciate the purplish hue of the emerging foliage. Alas, these are two things I did not do. Once the plant fully emerges, the foliage turns green. The flowers are similar to the straight species.
Dwarf Crested Iris (Iris cristata)
Short dwarf crested iris grows in shade and part shade in medium to moist soils and blooms well in both. It is short, reaching just 6" in height. It grows by rhizomes and spreads nicely once established. It blooms in mid-spring. In Alice's garden above, a handful of plants formed a colony on a shady slope over the course of several years on their own. This plant actually makes a great groundcover.
This is what dwarf crested iris looks like when it first emerges in spring. You can easily cut off portions of rhizomes with new growth and replant to spread or add plants to a different area of your garden. I wouldn't try this until your plants seem to be fairly well established, two years in or so.
Where to Get This Plant
Most native plant nurseries carry both the taller and short iris. Garden Centers will sometimes offer these plants but more typically sell Siberian iris (Iris siberica) which can look very similar to northern blue flag though with a deeper purple flower and it is easy to confuse the two.
On-line, blue flag iris is available in quarts from Direct Native Plants in Middle River, Izel Plants based in Washington D.C. as plugs, and dwarf crested iris, northern blue flag iris and blue flag 'Purple Flame' are all available from Plant More Natives in Richmond.
As always, your native plant nursery is your best source and the straight species is the best choice. Bona Terra in Anne Arundel County, 10 minutes from North Beach, is open now, and has northern blue flag in quart, gallon and three gallon sizes. You can buy now and pick up later in spring. Just an idea!