A sure sign that the garden season had begun was a bed of blooming bearded iris, commonly called flags, in grandma’s garden.
Iris are well-loved perennials in the home landscape. The iris genus contains almost 300 species, with new hybrids appearing each year.
The bearded or German iris, Iris germanica, is the most common species, but quite a few others perform just as well. Most species of iris are perennial plants that can be divided into two distinct types — rhizomes and bulbs. The common bearded iris is one of the rhizomatous types, grown from a rhizome, an elongated stem planted at the soil line. Other rhizome forms are the Louisiana iris, Japanese and Siberian iris and the native woodland crested iris. Less common are bulbous iris, which include the Dutch and the Reticulated iris.
All iris plants are monocots, meaning their flower parts are in groups of three. Three sepals face downward and are referred to as falls, while the three petals that face upward are referred to as standards. While most iris plants thrive in full sun, the woodland crested iris will do well in partial shade. Planting depth will vary by species as well.
While the tall bearded iris is the most common, there are actually six different classifications of bearded iris based on size: miniature dwarf, dwarf, intermediate, miniature tall, border and tall. Bearded iris typically bloom for 2 to 5 weeks, depending on the vigor of the plants. When planting, choose early, mid-season and late-blooming varieties to extend the flower display.
The common name “bearded” comes from the bushy “beards” that appear on the falls of the flower. The rhizomes of the bearded iris plant are planted shallowly, with a portion of the rhizome exposed above ground. Bearded iris like a well-drained, light soil with at least 6 to 8 hours of sunlight a day, and no mulch should cover the rhizome. Start with a weed-free, grass-free site, and monitor it frequently. Apply a complete fertilizer in the spring and again a month after bloom. Avoid putting the fertilizer directly on the rhizome.
Iris rhizomes multiply horizontally and can form a mat of rhizomes over time. If they get too crowded, they will stop blooming. Bearded iris should be divided every three to five years, or sooner if their blooms begin to decline. Division is best from the middle of July through mid-August. You want to give the plants time to reestablish themselves after transplanting before winter sets in.
Consider trying some of the other iris species. Our native crested iris is a much smaller plant that thrives in the shade. It only grows 6 inches tall, and the rhizomes are near the surface but can be covered with soil or leaf mulch. It has lovely clusters of light blue flowers, which last for 2 to 3 weeks in the spring. After bloom, the grass-like foliage can serve as a groundcover. It does best in a well-drained but rich site.
Beardless iris rhizomes include Louisiana, Japanese and Siberian iris plants. Siberian iris like even moisture, while Japanese iris like as much water as you can provide, but neither likes to have wet feet in the winter. Louisiana iris will grow in standing water year-round but will also do well in the ground if they don’t dry out. Louisiana iris need 6 to 8 hours of sunlight a day, but protection from the hot afternoon sun is beneficial. Japanese iris and Siberian iris thrive in full sun, and are somewhat similar in appearance. Typically, the flowers are much larger on Japanese iris than Siberian iris, and the plants are taller. Both are heavy feeders and should be fertilized with a complete fertilizer in the spring and just before blooming.
If you want to learn more about these flowers, consider joining a local iris society; there are several in the state. Here is a link to the Central Arkansas Iris Society: centralarkansasiris.org.