In the Garden: (Almost) All the Colors of the Rainbow

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Irises. Photo: Charles Kidder.

Iris was the mythological goddess of the rainbow, messenger of the gods of Olympus. With the great variety of colors present across its hundreds of species, it’s not surprising that a plant genus was also given the name Iris. Conveniently for us, iris serves as both the common, as well as the scientific name for these plants. As for the rainbow of colors: even iris aficionados would have to admit that none are truly red; a coppery-chestnut is about as close as they come.

The two to three hundred iris species occur naturally across much of the Northern Hemisphere.  Some species hybridize naturally, and thousands of cultivars are available from specialty growers.  No matter what conditions your garden presents—sunny or shady, wet or dry— you should be able to grow some type of iris.

The bearded iris group—hybrids rather than an actual species—are still the most popular irises grown in the United States. They come in a bewildering number of varieties, differing primarily in height and flower color. Plant height for bearded irises is broken down by such terms as Dwarf, Intermediate, Tall, etc. (To a non-believer like me, they could be classified as Short, Tall and Everything-in-Between.) Flower color is all over the spectrum, ranging from subdued monochromes to combinations that could charitably be described as over-the-top.

Bearded iris prefer good drainage and even moisture; unlike some iris species, they don’t like to be soggy. When planting, the rhizomes—underground stems—should be partly exposed. And contrary to all that we’re taught regarding the importance of mulching, do not put mulch on bearded iris.  This only encourages problems, and this group is susceptible to many.

What if you’d like to be adventurous and try something other than the bearded irises? Many good choices are available, although you might have to search them out. If you can provide consistent water, consider the Louisiana irises, a group of species and hybrids native to the Mississippi Valley and Southeast Coast.  The variety ‘Ann Chowning’ comes close to a true red, while ‘Black Gamecock’ is a stunning black-purple.

A couple of small irises are native to the woodlands of the Eastern United States. Iris verna, Dwarf Iris, grows in dry, acidic, rocky woodlands and demands good drainage.  Flowers are deep-to-light blue with an orange blotch. The Crested Iris (I. cristata) is similar, but spreads quickly via its rhizomes in shaded to part-sun conditions. The light blue flowers have a yellow crest.

Flowering in very early spring, the Reticulated Iris (I. reticulata) is a welcome relief from the drabness of winter. Deep-purple-and-gold flowers reportedly have the fragrance of violets, but my nose cannot attest to that. Grass-like blue green foliage disappears by mid-spring, so surrounding plants can fill in the space.

If you’re willing to stretch your hardiness zone a bit, the Algerian Iris (I. unguicularis) can bloom off-and-on during mild winter weather. Flowers are almost stemless, so they’re partly hidden among the evergreen foliage; this iris demands to be admired at close range.

I’ve been growing the Roof Iris (I. tectorum) in my garden for a few years and have been pleased with its performance. The straight species has lilac flowers mottled with dark blue blotches; my pass-along plant is variety alba, with white flowers. Roof Irises prefer full sun and good drainage, although mine have done well in partial shade. In Japan they were grown on the edge of thatched-roof houses.

Hailing from Central Europe and Russia, the Siberian Iris (I. sibirica) typically has blue-purple flowers, but many cultivars are available. They do well in a bog garden, but tolerate normal soils if watered during dry spells. Compared to the tall bearded types, they provide a more delicate appearance and are less susceptible to soft rot or borers.

Two native irises are especially suitable for growing at the edges of ponds or streams.  The Northern Blue Flag (I. versicolor) and the Southern Blue Flag (I. virginica) have natural ranges that intersect in Virginia. Both of these plants are superior to the Yellow Flag Iris (Iris pseudacorus), a highly invasive species from Eurasia. Do not plant it!

Irises are a highly diverse group of plants with differing growing requirements, and additional information may be obtained from such groups as the American Iris Society. But beware. Allan Armitage, perennial plant authority, had an interesting comment on people afflicted with “irisitis.”  “Those so affected have been known to babble incomprehensibly about amoenas, plicatas and selfs, but they can be safely approached.” Maybe in the age of websites, we should be grateful that one needn’t approach them directly at all.  

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