2020: Year of the Iris

Year of the Iris

Irises are among the easiest of perennials to grow from bulbs, roots or rhizomes. The genus includes some 250–300 species featuring showy flowers. In fact, the iris takes its name from the Greek word for a rainbow, which is also the name for the Greek goddess of the rainbow, Iris. A perfect name for flowers that bloom in a rainbow of colors!

Irises are native throughout the Northern Hemisphere, with most of the species being of Eurasian origin. 

Each iris flower has two types of flower parts, the “standard” stands upright and includes 3 petals. The “falls” curve outwards and downwards and are made up of 3 sepals.

The three main types of garden iris are Bearded and Beardless, both with rhizomes, and Bulbous. Each has distinct features to complement your garden.

Plant Iris Depending on When You Want Them to Bloom…

• Reticulate—Late winter/very early spring
• Dwarf Bearded—Early to midspring
• Tall Bearded—Mid to late spring
• Siberian—Late spring to early summer
• Dutch—Late spring to early summer
• Japanese—Early summer
• Louisiana—Early to midsummer
• Reblooming Bearded—Midspring and again in late summer to early fall

Bearded Iris

Bearded irises, including the common garden iris or German bearded iris (I. × germanica), are identified by thick, bushy “beards” on each of the falls (sepals) of the blossoms. These hair-like beards are fuzzy and stand up from the sepals.

The German bearded iris (I. × germanica) is a natural hybrid, derived from a long-ago cross between the pale purple-flowered Dalmatian iris (I. pallida) and the yellow-flowered Hungarian iris (I. variegata). It now comes in a huge range of colors and some 30,000 varieties. It’s hardy in USDA hardiness zones 3 to 10.

It has been crossed with other species, notably with the pygmy iris (I. pumila), giving rise to the great variety of modern dwarf and median bearded iris cultivars.

Bearded irises are grown from a thick fleshy mostly underground stem called a “rhizome”. The rhizome feels like a tough potato in texture. These rhizomes should be planted in the ground during the fall months to give the roots time to become established before winter. When you buy a new iris by mail order, you’ll probably receive a rhizome with clipped roots and leaves. It can remain out of the ground for a week or two without serious harm, but the sooner it is planted, the better.

Plant your bearded iris in a sunny (6–8 hours) location with well-drained soil planted with the top of the rhizomes at the soil level or up to an inch (2.5 cm) below the surface of the ground. 

Bearded irises do best with an all-purpose fertilizer, applied once in early spring and once after blooming.

In about 2 or 3 years, a decrease in blooms usually indicates that it is time to divide your plants. Be sure to divide the plant by cutting the newer parts of the rhizome free from the old section and discard the older part.

Bearded irises are commonly divided into six groups depending on the size of the flower and the height of the plant.

1. Miniature Dwarf Bearded
2. Standard Dwarf
3. Intermediate Bearded
4. Border Bearded
5. Miniature Tall Bearded
6. Tall Bearded

Each one of these classifications have a different flowering time, height and habitat. 

Some bearded irises are “rebloomers”, blooming once more in the same growing season in the summer or fall. The number of blooms you will get later in the season varies by variety and local conditions. There are now reliable and attractive rebloomers available in the marketplace which will perform in most climates, but although they can’t be counted on in colder ones (USDA hardiness zones 3 to 5). You’ll probably see the term “reblooming iris” on the label.

Beardless Irises

Often used for naturalizing or perennial borders, beardless irises are an easy and beautiful addition whether in bloom or not.

Though beardless irises are often called “water irises” and many do grow in marshy conditions in the wild, most varieties do great in regular home gardens. They enjoy a full to partial sun location and a balanced fertilizer in the spring when the plants are a few inches high. Japanese Irises are especially heavy feeders and appreciate a second feeding of fertilizer before bloom time. During dry periods, mulch the roots to help retain moisture.

If you buy your beardless iris in a pot, it can be planted at any season. Just plant it at the same depth in the garden as it was in the pot. 

If you receive a rhizome by mail order, though, it will likely be shipped in the fall wrapped in damp paper and placed in a plastic bag. Immediately remove the rhizome and soak the roots in water overnight. These roots do not like to dry out, so plant immediately, at the latest about four weeks before the first hard freeze. Beardless rhizomes like to be planted at a depth of 1? (2.5 cm) (2?/5 cm for Japanese iris).

Beardless irises can grow for many years in the same location. Japanese irises are the exception—they like to be divided every three years.

There are six main types of Beardless Iris.

The first four types are commonly grown in gardens, and they all bloom late spring and early summer. The fifth type, the Pacific Coast Native, is native to the western regions of the United States and is not as well known. The sixth is Other and includes many of the flag irises seen in the wild.

1. Spuria Iris (I. spuria), USDA zones 5 to 9
2. Siberian Iris (I. sibirica), USDA zones 3 to 8
3. Japanese Iris (I. ensata), USDA zones 4 to 9
4. Louisiana Irises (I. fulva, I. brevicaulis, I. nelsonii, I. hexagona, and I. giganticaerulea), USDA zones 5 to 9
5. Pacific Coast Natives or Californicae (I. bracteata, I. chrysophylla, I. douglasiana, I. fernaldii, I. hartwegii, I. innominata, I. macrosiphon, I. munzii, I. purdyi, I. tenax, I. tenuissima and I. thompsonii), USDA zones 7 to 10
6. Other beardless irises (includes yellow flag [I. pseudacorus], blue flag [I. versicolor], rabbitear iris [I. laevigata] and Virginia iris [I. virginica]), USDA zones 3, 4 or 5 to 9

Bulbous Irises

These irises come from drier climates than the others and form a true bulb with a papery outer coating rather than a rhizome. They are generally sold as dry bulbs in the fall, along with tulips and narcissus.

They dry prefer conditions in the summer months, when they go fully dormant, losing their leaves.

There are two main types of bulbous irises.

1. Dutch iris (I. × hollandica and related species)
2. Reticulate irises (I. reticulata, I. danfordiae and others) 

Dutch irises are usually sold in the fall, but specially treated bulbs may be available in the spring. Plant the bulbs about 5? (12 cm) deep with the pointed tip up.

These irises are a popular cut flowers, used by florists in seasonal flower designs. They flower in late spring to early summer and can be grown in sun or partial shade. The bulbs are hardy in USDA hardiness zones 6–9, surviving only sporadically in colder zones. However, even in the best of conditions, they tend to be short-lived, often blooming only once, and are therefore often used as annuals.

Dutch Irises look best when planted in groups. For a stunning show, plant about a dozen bulbs per square foot.

Reticulate irises are small plants with netted bulbs (that’s what reticulate means) that bloom in earliest spring, sometimes even late winter. They need full sun in spring and dry summer conditions. Most are hardy from zones 4 to 9 and can live for decades, often spreading. They are at their best in rock gardens and garden borders.

Even More Irises

There are many other irises to discover. Once you’ve tried a few of the more common ones described above, you’ll certainly want to get to know even more of the iris world in this, the Year of the Iris!

Unless otherwise noted, all photos are courtesy of the National Garden Bureau.