Iris: More than meets the eye

Iris is a genus of herbaceous perennial flowering plants that is popular in many gardens. Some misconceptions about irises seem to persist even though irises are one of the most recognizable groups of plants for many gardeners. One of these is that irises are bulbs, when in fact the underground portion of their stem is a rhizome rather than a bulb. This may seem a small distinction, but in the case of irises, it is an important one. Rhizomes are lateral stems and often grow at or just below the soil surface. For most types of iris, it is generally recommended to plant the rhizome so that just the top portion is visible at the soil surface and the rest is buried underground. If the rhizomes are buried too deeply, the plants often have reduced bloom or no bloom at all.

The second misconception is simply that irises are all the same, rather than a large genus encompassing many different and varied species. What comes to mind most frequently when people think of iris is the bearded iris, Iris x germanica. Iris flowers typically have three petals pointing upward, known as 'standards' and three petals that hang downward, known as 'falls.' Bearded irises are characterized as having a line of hairs at the base of the falls that resembles a beard. Bearded irises grow best in average to dry soil and full sun, may grow as much as foot feet tall, and come in a plethora of color combinations. The species name germanica implies that bearded irises are native to Germany. However, this species actually traces to Yugoslavia.

Top: The flowers of a Bearded Iris typically have three petals pointing upward and three petals that hang downward. Photo: S. Strine, CC BY 2.0
Above left:  Iris hexagona has narrower leaves, smaller flowers, no beard, 

prefers wet soil to dry, and is native to the Southeastern United States, though not North Carolina. Photo: M. Manners, CC BY 2.0 Above right: Iris cristata is a shade-loving iris that is native to North Carolina. Photo: CC BY 2.0  Right:  Iris japonica is another shade-loving iris. It grows to about a foot tall. Photo: K. Andre, CC BY 2.0

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Louisiana iris, Iris hexagona, is not nearly as common, but is different in almost every way. It has narrower leaves, smaller flowers (the standards, in particular are quite small compared to the falls), no beard, prefers wet soil to dry, and is native to the Southeastern United States, though not to North Carolina. Flowers are lavender to dark purple. The Louisiana iris likes full sun and grows upright to about 3 feet, so there are at least some similarities. Iris versicolor, Iris laevigata, Iris ensata, and Iris pseudacorus all grow in standing water and are used in rain gardens and/or water gardens, though the last of these four is considered an invasive plant and should be avoided.

Are there iris esthat like shade?  Yes, at least two species, Iris japonica and Iris cristata. Both are shade-loving irises that also are low-growing spreading types. Iris japonica grows to about 1 foot tall and has flowers that can range from white to pale blue or purple, and Iris cristata is even shorter, at 6-9 inches tall and with a range of colors from white to pink to purple to even yellow. Iris cristata is native to NC and much of the Southeastern US, while Iris japonica is native to Japan, but both fill the same niche as flowering groundcover for shady areas.

There's also Iris domestica aka Blackberry Lily, with its pretty orange flowers and odd blackberry-like fruit, and Iris unguicularis, the Winter iris ,which blooms blue in, you guessed it, winter. Suffice to say, you may think you know Iris, but there may be more than meets the eye.

Matthew Stevens is the County Extension Director and Horticulture Agent for North Carolina Cooperative Extension’s Pitt County Center. If you have questions about this article or gardening in general, please contact the Pitt County Extension Master Gardeners at [email protected] or 252-902-1705.