Bearded irises are, undoubtedly, the tall standouts of the spring bulbs, with their showstopper flowers, complete with the ruffled edges that give them their name. If you’re looking for more variety, though, the iris family has plenty to offer. Beardless irises, such as Japanese irises, the native Louisiana and Pacific Coast irises, Siberian irises and spuria irises, are rapidly becoming more popular. Other choices include the familiar Dutch and Spanish irises, the English irises and the increasingly popular reticulata irises.
Fall is the standard planting time for irises, although some can also be planted in early spring. You should begin planting bearded irises in summer in the coldest-winter climates. You’ll be rewarded with blooms for years to come.
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Iris basics. The bulb type, growing conditions, watering needs and bloom times may vary, but the two things all irises have in common are their tall, narrow, upright to arching leaves and their flower structure. Their three inner petals are true petals, growing upright, arching or sometimes growing sideways. The outer segments of the bloom are not petals but sepals, also known as falls. On bearded and crested irises, these are ruffled or have a comb-like appearance.
Beyond that, the 250-plus species of iris can provide variety and continuous bloom in your garden. Choose from bearded or beardless irises, both of which grow from rhizomes, or opt for bulbous irises, which grow from true bulbs.
Irises are known for their flowers in shades of blue and purple, but you can find flowers in almost any color. With judicious choices, you can also plan for blooms throughout the spring and into summer.
Benefits and tolerances: As befits such a varied group of plants, irises can handle a range of growing conditions and different soils, although most insist on good drainage. They’re relatively deer-resistant, and many, especially the bearded irises, are drought-tolerant. They’re also fairly pest-free, with iris borer being the biggest concern.
Bearded Irises
Origin: Southern Europe and the Mediterranean
Bloom season: Midspring, although remontant irises will rebloom in summer, fall or even winter
Where they will grow: Hardy to minus 40 degrees Fahrenheit, or minus 40 degrees Celsius (USDA zones 3 to 10; find your zone)
Water requirements: Water regularly when plants are growing and blooming; cut back after bloom and through winter
Light requirements: Full sun; filtered afternoon shade if summers are hot
Bulb type: Rhizome
When to plant: July to October; plant in July and August in the coldest-winter climates; plant in August to October in other climates, waiting until later in October in the warmest climates
Cautions: These rhizomes aren’t edible, and some people develop dermatitis from contact with them.
Bearded irises come in an astonishing array of sizes and colors. They are generally divided into four categories:
○ Tall bearded irises reach between 2 and 4 feet tall. They bloom in midspring, although some will also rebloom later in the year in the right conditions.
○ Median irises — border bearded irises, intermediate bearded irises and miniature tall bearded irises — are smaller, between 8 and 28 inches tall.
○ Dwarf types include the standard dwarf bearded irises, which flower on stems that are 8 to 15 inches tall, and miniature dwarf bearded irises, which reach only 2 to 8 inches tall.
○ The fourth category includes aril and arilbred irises. The Regelia group of aril irises and the arilbred irises, which are hybrids, need good drainage and alkaline soil; otherwise, their care is similar to bearded irises. The Oncocyclus group of aril irises is very particular about growing conditions, including soil, sun and summer water.
Planting notes. Choose a spot in full sun with good drainage. You may need to plant in raised beds or on hills if you have heavy clay soil. Set the rhizomes 1 foot to 3 feet apart just below the soil, with the leafy part pointed in the direction you want the plant to grow. Point the leafy part uphill if you’re planting on a slope.
Water thoroughly after planting. If the weather is hot, provide shade so the rhizomes won’t get scalded. If you have cold winters, cover the soil with mulch to protect the rhizomes.
Caring for bearded irises. Water sparingly after planting until the rhizomes set their roots. Then water regularly until it begins to rain or the ground freezes. Resume watering when growth begins, and water regularly throughout the growing and blooming season and an additional six weeks after blooms fade. Then water about once every couple of weeks if it’s warm to once a month if it’s cool. Shade the plants from afternoon sun in the hottest summer climates.
Feed with a neutral or low-nitrogen fertilizer when the plants begin to grow in spring and then again once they’ve finished blooming. Remove old or dead leaves in fall. If leaves show signs of leaf spot, apply a fungicide. Divide crowded clumps every three to four years.
Beardless Irises
Origin: Japan, Central Asia, Europe and North America, depending on species
Bloom season: Mid- to late spring
Where they will grow: Varies by species
Water requirement: Regular to ample
Light requirement: Full sun to light shade
Bulb type: Rhizome
When to plant: Varies by species
Beardless irises lack the ruffled edges that characterize their bearded cousins, but that might be the only thing that binds them together. The hybrids are broken into five groups; a number of iris species are often included in the overall category as well.
Japanese iris. Sports broad flowers set on stems that can reach 4 feet tall. Colors include white, pink, blue and all shades of purple; flowers appear in late spring. Japanese irises like it to be wet; they are a good choice for along the edges of ponds or sunk into ponds. They’re hardy to minus 40 degrees Fahrenheit, or minus 40 degrees Celsius (zones 3 to 9).
Plant in full sun or, in areas with warm summers, in a spot where they’ll get light shade or filtered afternoon sun. The soil should be neutral to slightly acidic, and unlike most irises, they don’t mind wet feet. Plant 2 inches deep and 1½ feet apart in moist, neutral to acidic soil, with the leaf ends pointed in the direction you want them to grow. You can also plant up to three rhizomes in a 12-inch container. September to November is the best time to plant, but they can be set out in spring as well.
Provide ample neutral to acidic water throughout the growing and blooming period. Divide in fall when they get crowded.
Louisiana iris. Sometimes called swamp iris, Louisiana iris does well in more humid conditions. It does best in zones 3 to 9 and can be happy in climates as diverse as those of southern South Dakota, Maine, Hawaii and Florida. Louisiana irises reach 2 to 5 feet tall. The flowers come in almost as large a color selection as bearded irises, with blooms appearing in May and June.
Plant in August and September. Look for a location in full sun with rich, well-watered, neutral to acidic soil. Like Japanese irises, they can handle growing in water. If your summer afternoons are hot, provide light or filtered shade. Soak the rhizomes and plant them about 1 inch deep and 12 to 18 inches apart. Provide regular water and add mulch in late fall if the ground freezes in winter.
Pacific Coast iris. Pacific Coast irises are perfect additions to woodland and rock gardens. These West Coast natives and their growing number of hybrids are noted for their slender foliage and flower stems reaching 8 to 24 inches tall, as well as their flowering period, which can last from January to June. They do best in zones 7 to 10.
These irises need full sun and very well-draining soil; you may need to grow them in raised beds if you have clay soil. You can plant from containers at any time, preferably in spring or fall, but October is the prime time for planting rhizomes; plant about 1 to 2 inches deep and a foot apart. Provide moderate water while they’re growing and none in the summer.
Divide when new roots are forming, which will be anytime from early fall to midwinter; you’ll need to scrape away the soil to check on the roots.
Siberian iris. This iris has grassy foliage that grows from 1 foot to 3 feet tall and flowers in shades of white, purple, pink, blue and even light yellow, on stems ranging from 14 inches to almost 4 feet tall. Expect between two and five flowers on each stem in June and July. Siberian irises are hardy to minus 30 degrees Fahrenheit, or minus 34.4 degrees Celsius (zones 4 to 8). They look their best when planted in clumps.
Plant in late summer (or early spring) in cold-winter regions. Wait until fall if you live where summers are hot and winters are mild or moderate. Choose a spot in full sun or with light afternoon shade if summers are hot. Siberian irises do best with neutral to acidic soil. Set the rhizomes about 1 to 2 inches deep and space them 1 foot to 2 feet apart. Water thoroughly after planting, and provide plenty of water when plants are growing and blooming; cut back after that. Divide in late summer or fall when the centers of the clumps no longer produce.
Spuria iris. It would be easy to mistake spuria irises for Dutch irises. Their leaves reach 3 to 4 feet tall and, thanks to hybridizing, flower colors range from yellows and bronzes to reds, purples and grays in late spring and early summer. These irises are hardy to 10 degrees Fahrenheit, or minus 23.3 degrees Celsius (zones 6 to 9).
Plant rhizomes in late summer or early fall. Choose a spot in full sun with neutral to slightly alkaline soil. Set rhizomes 2 inches deep and 1½ to 3 feet apart. Provide regular water while they’re growing and blooming, but spuria irises do best with almost no water in summer. Add fertilizer in early spring and fall. Provide winter protection if temperatures drop consistently below freezing. Divide in late summer or early fall only when they become overcrowded.
Bulbous Irises
Origin: The Mediterranean, especially Spain, Russia, the Caucasus and northern Iran, depending on species
Bloom season: Early spring to summer, depending on species
Where they will grow: Hardy to minus 10 degrees Fahrenheit, or minus 23 degrees Celsius (zones 6 to 9)
Water requirement: Regular to ample water while plants are growing and flowering
Light requirement: Full sun to light shade
Bulb type: True bulb
When to plant: Varies by species
Dutch, Spanish, English and reticulata irises all grow from true bulbs, which become dormant in summer. All of these are beardless. Dutch iris may have the highest name recognition, but reticulata irises are also popular.
Dutch and Spanish irises. These are the familiar irises sold by florists. They come in a range of colors, including white, yellow, orange, blue, purple and brown, as well as bicolors. The flowers are held on stems that reach about 1½ to 2 feet high. Bloom times range from March in warmer climates to May or June in colder climates. Spanish iris are similar, though with smaller flowers and a bloom time that begins about two weeks after that of Dutch irises.
Plant both in October and November in a spot with full sun and well-draining soil. Set bulbs 4 inches deep and 3 to 4 inches apart. Add mulch for winter protection in cold-winter areas. Water generously when the plants are growing and blooming, then don’t water at all during their summer dormancy. If needed, dig up the bulbs after the foliage has finished and store them in a cool, dry place before replanting.
English iris. These irises are similar to their Dutch and Spanish cousins, but have broader flowers and summer blooms. They can also handle some summer water.
Plant in fall in a spot in full sun or with afternoon shade in the hottest climates and with cool, moist, acidic soil. Set bulbs 3 to 4 inches deep and 4 inches apart. Provide ample water during the growing season. In regions where summers are wet, you may want to dig these up and replant.
Reticulata iris. This is a small iris, usually not reaching more than 8 inches high, with equally small blossoms. Reticulata irises are perfect for containers, edgings and rock gardens. They’re also unusual in that the leaves may not appear until after the flowers bloom. Violet, blue-violet and white flowers are the norm in late spring and summer, although there is a species with yellow flowers.
Plant in fall in a spot in full sun with well-draining soil. Set them 3 to 4 inches deep and 3 to 4 inches apart. Provide regular water from fall through spring, but let the soil stay dry in the summer; you may need to dig and store the plants if you get summer rains. Watch out for snails and slugs.
How to use them. Plant in drifts or clumps for a natural look or intersperse with other spring-flowering annuals, perennials and bulbs in garden beds and borders. Smaller irises, such as reticulata irises, can be grown in containers or nestled into rock gardens. Choose a single color to make a statement, or mix and match for a cheerful array.
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If you’re willing to make inroads into your outdoor display, you can use irises for stunning indoor arrangements.