Bearded Iris: A Perennial Rainbow for Your Garden

The bearded iris is always an indication in my region that spring has arrived. All over neighborhoods in the town, tall bearded iris blooms in a multitude of colors. Up to that time, they’ve been dormant, and their green foliage has been the only emergence.

Not only do bearded iris plants return annually, they sometimes put on a show twice a year in spring and fall. As the flowers fade, gardeners know they’ll have more in the next flowering period. People also grow bearded iris because they can plant multiple colors in one space. 

In this piece, we’ll discuss growing bearded iris. We’ll cover a few of the best cultivars out there, and talk about how to care for them, so you can enjoy them for years to come. 

Bearded Iris Quick Care Guide

All About Bearded Iris

The bearded iris plant has a fascinating mythological origin. The Greek goddess Iris would descend to Earth on a rainbow to deliver messages from the gods to the humans. Wherever she landed, varicolored flowers sprang to life. This makes a lot of sense, knowing that “iris” is the Greek word for “rainbow.” You can definitely grow your own rainbow using just irises.

Their everyday history is no less fascinating. The Egyptian King Thutmose III conquered Syria and brought back irises to his garden. To the Egyptians, irises represented life essence and renewal, so it’s no surprise they used the rhizomes to make medicines and incense for religious rites.​

Bearded irises came to America with European settlers in the 1600s, but they were especially adored by physician and professor Michael Foster in the late 1800s. His student, William R. Dykes brought about the iris’ advancement with his book The Genus Iris.​

Bearded iris plants are perennials, and every type is a reblooming iris. They emerge from rhizomes in spring, and their flowers last until late spring and sometimes mid-summer. Some produce a second bearded iris bloom in fall as well. Their leaves grow up to 3 feet tall, and each rhizome produces a plant that spreads up to 1 foot wide. 

The leaf structure is a fan of folded and flattened light green foliage. The matte, palm-like leaf surfaces of bearded irises grow perpendicular to the root. Within this fan, flower stalks emerge, which are produced when the rhizomes elongate. There may be multiple flowers that bloom on a single stem, but they always begin at the top. 

Bearded iris leaves last throughout the fall in most areas. They’re perfect planted around trees or in perennial borders. Because they’re deer-resistant, you can use them to keep deer out of other plants. Plant irises anywhere you want to see them bloom in spring and fall.  

Bearded Iris Varieties

The American Iris Society has identified 8 different varieties of beared irises – all are reblooming iris types. Let’s talk about those now!

• Tall miniature dwarf bearded iris: the miniature dwarf bearded iris grows to about 24 inches tall and blooms in a good-sized clump later than other irises in late May through June. They have smaller flowers and more spindly stems. Iris Piazza Del Campo is a lovely purple tall bearded iris with surrounding pink-violet petals.     
• Standard dwarf bearded iris: the standard dwarf bearded iris grows no taller than 15 inches. Try the stunning Boil and Trouble cultivar, which is a standard dwarf that has dark maroon flowers that have an electric blue bearded center. 
• Intermediate bearded iris: the intermediate bearded iris is also about 2 feet tall and blooms in April through May. The flowers and plants themselves are well-proportioned and come in tons of colors. For a contrasting blue and white flower, try Iris Rimaround.  
• Miniature tall bearded iris: the miniature tall bearded iris is about two feet tall and is considered the best tall bearded iris in table flower arrangements or evergreen boughs. Try the Off The Grid cultivar for upright yellow-salmon blooms.  
• Border: like a tall bearded iris, these grow up to 2 feet tall. They’re great in perennial borders and flower May through June. Iris Lady of the Night has deep purple flowers with a stunning yellow stamen.  
• Aril or Arilbreds: these are hybrids of bearded irises and aril irises. The latter have arrays of color and shape. With these, you have many more choices than you would with the others listed here. Iris Sun and Snow brings lightness to a garden with its white and yellow flowers.  

Caring for Bearded Iris

Growing bearded irises is simple. Let’s discuss the basic needs for those planted in the garden. 

Sun and Temperature

Irises have a wide hardiness range, from zones 3 to 9. They love six to eight hours of partial or direct sunlight daily where they are planted. As long as you’re not in a climate with hot summers, find a spot where the full sun will hit them. However, in regions with cold winters, too much shade will prevent flower production.

The temperature tolerance of bearded irises reaches -25° Fahrenheit. Those plants in direct light during late summer may have scorched and dried leaves. The same goes for winter. Most of the time, irises go dormant to return in fall or spring.

Water and Humidity

When in doubt, err on the side of inadequate when it comes to water. Fewer deep waterings are better than many shallow ones. Water new plantings when the top three inches of soil dries out. After the first rain, cut back your schedule. 

I can attest to the drought-tolerant nature of bearded irises. As long as good drainage is present, they often don’t need a schedule. If you want to water them regularly, do so once a week in the morning with soaker hoses or drip irrigation at their base. Avoid wetting the foliage. Overwatering encourages bacterial rots that damage the rhizome. Similarly, if you’re growing in a humid area, there may be no need to water at all. 

Soil

Irises hate standing water and soggy rhizomes. To ensure adequate drainage, plant on a slope or in a raised bed. Adding compost to the soil can improve drainage. Gypsum added to heavy clay soil will keep it well-drained. Add sulphur if your soil is too alkaline, as irises like acidic soil at roughly 6.8 pH.

Plant bearded iris in well-drained soil. Loose soil is best, as the rhizome struggles to produce leaves in compacted soil. Before planting your rhizomes, aerate the soil, and amend it lightly to ensure the best possible growth. For a geographic location with cold winters, mulch around the base of your plants after they emerge in spring. This protects them and keeps them warm.  

Fertilizing Bearded Irises

Too much nitrogen encourages the rhizome to produce leafy growth and can make plants susceptible to disease. A salt-free alfalfa or bone meal applied once in early spring before the growing season begins and then in early fall is good. 

Irises don’t need fertilizer often, and a light application of a high potassium and phosphorus blend is best. Avoid applying fertilizer in the winter or late fall when the rhizome has entered dormancy. Most people reapply a layer of compost in fall and early spring to give the plants a nutrient boost. 

Pruning Bearded Iris Plants

In the fall, cut back the large clumps of leaves to 3 inches so the iris can use its energy for root growth instead of foliage. Remove damaged or dead leaves from the garden throughout the growing season. Deadhead the flower heads of bearded irises, but keep the foliage at full size throughout the summer into the first part of fall. 

Bearded Iris Propagation

Bearded irises are best propagated by division of the rhizome. After three or four years, separate crowded irises and replant them with more space between each. A good time to do this is when they are dormant in July or August or in winter if it’s too hot where you live (like it is for me). 

Break apart the rhizomes or cut them with a knife, leaving a fan of leaves on each. Trim the leaves to three inches and leave the bulb in the shade for a few days to a week to allow the cuts to heal. Keep plantings 12 to 18 inches apart, and place them 4 inches below the soil level. This ensures you don’t overcrowd newly planted bearded iris rhizomes and make way for new growth in spring.

Troubleshooting Bearded Irises

Even though there are several pests and diseases to look out for on your bearded iris, you may not have to deal with any of them. We’ll cover them here so you know what to look for. 

Growing Problems

A common mistake people commit when growing these flowers is not giving them enough sun. If you don’t live in hot USDA zones, bury your rhizomes in full rays of sun. Alternatively, if you live in a hot zone, put them in partial shade.

Another issue gardeners may have with bearded irises is allowing the plants to take over the garden and get overcrowded. Not only does this provide conditions for fungal diseases to proliferate, it stunts any potential new growth. Because it is a perennial, divide bearded iris every few years to keep every iris healthy. If you have a ton of rhizomes, give them away to friends!

If you plant your rhizomes too deeply, flower production will slow the following year. Dig up the rhizomes in your garden during the summer or winter, and replant them 4 inches below the soil line. They’ll flower in the following blooming period.  

Pests

The iris borer is the larva of a moth that lays its eggs on the leaves of irises in winter. In spring, the egg hatches, and the pinkish caterpillar crawls to the base to bore into the rhizome. Signs of iris borers include pinprick-sized holes in leaves, water-soaked spots, and slimy rhizomes.To control it, clean up garden debris. Destroy infected leaves. Use frosts to clean up beds, as the moth is not laying eggs at this time. 

The verbena bud moth is another huge pest of the iris. You’ll find these tiny brown caterpillars eating the buds of your plants in summer. They leave sesame seed-like frass behind. Control them by removing their gray or white eggs from the leaves. Hand pick them, or use Bacillus thuringiensis spray. Place your iris near plants that host beneficial predators to keep their population at bay. 

Whiteflies suck the sap from an iris but spray them with a strong stream of water for removal. Look out for white tiny moth-like creatures that scatter as you wave your hands through your plants to determine if this treatment is necessary. In my opinion, weevils are the cutest insects. But the iris weevil isn’t so cute when it’s feeding on the flowers of your blue flag iris. Control them by keeping the garden free of debris, where the weevil eggs overwinter.  

Thrips and aphids also find the leaves and sometimes flowers of irises tasty. Spray infestations with water to rip off their mouthparts and prevent further feeding. Or spray them with a systemic pesticide, like neem oil in the early morning before pollinators have had a chance to get to work for the day. A light misting is enough. 

Slugs and snails enjoy living in fallen iris leaves in damp gardens. Prevent their feeding on growing foliage by hand picking them off at dusk. Alternatively, place a beer trap in the garden to drown them. 

Nematodes may attack the rhizome of your iris, causing distortion and growth problems. You’ll probably notice them when you’re dividing in fall. You can treat the ground with beneficial nematodes, or remove all the healthy rhizomes and place them elsewhere while you solarize the soil over the course of a month. 

Diseases

Bacterial rot, specifically bacterial soft rot, generally arises when the iris borer is present. Control them to keep this disease at bay. If you water the plant too much, bacterial rots can set in as well. Keep the garden free of debris, and you’re good to go. 

Fungal leaf spot is caused by the pathogen, Didymellina macrospora. Fungal leaf spots begin as yellowish-brown spots with a water-soaked border. Leaf spot disease usually occurs in damp, cool weather, in gardens full of plant debris. Remove all rotten parts and fallen leaves from the garden soil, keeping it as clean as possible. Destroy infected plants to protect new plants from infections and prevent your irises from dying altogether.   

Frequently Asked Questions

Q: What is the difference between an iris and a bearded iris?

A: A bearded iris has a “beard”, or a large petal that spills below the top petals. 

Q: Do bearded iris need full sun?

A: Full sun is great, but in hot climates, they prefer some afternoon shade.

Q: Do bearded iris come back every year?

A: Yes! They are perennials. 

Q: How do you take care of bearded irises?

A: Plant them 12 to 18 inches apart in loose soil that is well-drained with plentiful organic matter. Water them seldomly, and make sure they have enough sunlight. Divide them in fall. You got this!

Q: What is the most beautiful iris?

A: Well, the bearded iris, of course! Truly, though, there are tons of bearded iris cultivars to choose from. 

Q: Do iris only bloom once?

A: No! Their bloom time, in springtime – and sometimes in fall – occurs every year. 

Q: When should you plant bearded iris?

A: Plant them in fall. This will give them enough time to get established before they flower in spring. 

Q: What month do bearded irises bloom?

A: They bloom from April through May and sometimes in fall months. This depends on the region in which they are planted.