Growing Irises

How to Plant, Grow, and Care for Irises

By Catherine Boeckmann
Iris Flowers
Pixabay

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The tall, beautiful iris, named after the Greek goddess who rode rainbows, comes in many magical colors. Despite its divine origins, this June bloomer is rugged, reliable, and easy to grow. Learn all about planting, growing, and caring for iris flowers. 

About Irises

There are some 300 species in the genus Iris. The most familiar irises are the tall bearded irises (Iris germanica) that reach 2 to 3 feet in height.

These distinctive, six-petaled flowers have three outer hanging petals (called “falls”) and three inner upright petals (called “standards”).

Irises may be bearded or crested (aka “beardless”). Bearded iris are so-called because they have soft hairs along the center of the falls. In crested iris, the hairs form a comb or ridge instead.

Most irises flower in early summer. Some—mostly bearded hybrids—are remontant, meaning they flower again later in the summer.

Irises attract butterflies and hummingbirds, and make lovely cut flowers. For iris companions in the garden, look to roses, peonies, and lilies.

Planting

When to Plant Irises

  • Ideally, plant irises in late summer to early fall, when nighttime temperatures remain between 40 and 50 degrees Fahrenheit or above. This gives them plenty of time to get established before the coming winter. The tall bearded iris varieties are best planted closer to fall because they go dormant in early to mid-summer.
  • If you receive bare rhizomes or irises in a container at some point earlier in the year, go ahead and plant them as soon as convenient. It’s better to get them in the ground rather than wait until the ideal time.

Choosing and Preparing a Planting Site

  • Irises will bloom best in full sun. They can tolerate as little as half a day of sun, but it’s not ideal. Without enough light, they won’t bloom.
  • Bearded irises must not be shaded out by other plants; many do best in a special bed on their own.
  • They prefer fertile, neutral to slightly acidic soil. Learn more about preparing soil for planting and organic soil amendments.
  • Good drainage all year-long is very important; irises prefer “wet feet, but dry knees.” They will not tolerate wet soil in wintertime.
  • Loosen the soil with a tiller or garden fork to a depth of 12 to 15 inches, then mix in a 2- to 4-inch layer of compost.

How to Plant Irises

  • For bare-root irises, plant the rhizome horizontally with the top exposed. In climates with hot summers, plant the rhizome just below the soil surface. 
  • Plant rhizomes singly or in groups of three, 1 to 2 feet apart, depending on the size.
  • Dig a shallow hole 10 inches in diameter and 4 inches deep. Make a ridge of soil down the middle and place the rhizome on the ridge, spreading roots down both sides. Fill the hole with soil and firm it gently, leaving part of the rhizome and the foliage uncovered.
    • Tip: It’s easy to make the mistake of planting irises too deeply. The rhizomes of these plants should be partially exposed to the elements, or thinly covered with soil in hot climates. If they’re buried too deeply, they won’t do well.
  • Do not mulch around the rhizome as this practice may encourage rot.
  • Water thoroughly.

Striped iris flower

Care

How to Grow Irises

  • Fertilize in early spring with an all-purpose fertilizer scratched in around the plants. Avoid applying high-nitrogen fertilizers to the surface or carelessly mulching with organic matter, which may encourage rhizome rot.  Reblooming Irises perform best if fertilized again after the first wave of flowering is finished.
  • Do not overwater irises; too much moisture in the soil can cause the rhizomes (roots) to rot. Water consistently and deeply, especially during summer drought.
  • Keep rhizomes exposed. Unlike bulbs, which thrive deep underground, iris rhizomes need a bit of sun and air to dry them out. If they’re covered with soil or crowded by other plants, they’ll rot. Irises may benefit from shallow mulching in the spring.
  • Taller irises may need staking or they will fall over. 
  • Watch for iris borers in the foliage (dark vertical lines that may appear watery show up in the leaves). See pest tips below.
  • Deadhead (remove spent blooms) consistently; Bearded Irises will flower sequentially on buds spaced along the stems.
  • After blooming is finished, cut flower stems down at their base, but do NOT trim iris leaves after they have finished blooming. Leaves carry on photosynthesis and generate energy for next year’s growth. Cut off brown tips—and cut the flowering stalk down to the rhizome to discourage rot.
  • After hard frost in the fall, cut foliage back hard, remove any foliage that appears spotted or yellowed and dispose of all debris in the trash.
  • If iris foliage is hit with heavy frost, remove and destroy it to eliminate borer eggs. See your local frost dates.
  • For winter protection, cover the rhizomes with an inch or two of sand topped with a light layer of evergreen boughs, applied after the ground freezes and removed when the Forsythias bloom the following spring.
  • In the early spring, remove winter mulch and any old foliage to allow for fresh, new growth and prevent Iris borers.

Dividing Irises

Over time, it’s not unusual for plantings of iris to become overcrowded, which causes the rhizomes to lose vitality and stop blooming. When this happens (usually every 2 to 5 years), it’s time to divide and replant healthy rhizomes in fresh soil. 

When to divide? Do this task after flowering finishes and then trim the foliage back to six inches. 

  1. Shortly after blooming (mid-summer), carefully dig up the clump of irises. You’ll find that the original rhizome that you planted (the “mother”) has produced several offshoot rhizomes.
  2. Separate these rhizomes from the mother with a sharp knife and discard of the mother, as it will no longer produce blooms. 
  3. Inspect the rhizomes for any rotting tissue or other signs of disease, removing and discarding infected parts or entire unhealthy rhizomes.
  4. Trim the iris foliage down to 3 to 5 inches in height so that the plants can focus on establishing new roots.
  5. Plant these fresh rhizomes in a new bed, replant them where they were before (after adding new soil), or share them with friends and spread the joy of irises!

irises-3530372_1920_full_width.jpg

Pests/Diseases

  • Irises are deer-resistant and drought-tolerant.
  • However, they are susceptible to the horrible Iris Borer which overwinters as eggs in spent leaves. If you see vertical streaks in the leaves, then look for these pests and squash them! If you see signs of rot in the rhizome, dig it up and remove the affected parts. 
  • Verbena bud moth, whiteflies, iris weevil, thrips, slugs and snails, aphids, and nematodes may also be troublesome.

Recommended Varieties

  • The tall bearded iris varieties come in flamboyant colors which lively up the June garden. They are June bloomers and generally planted only in the fall.
    • ‘Immortality’ is a tall bearded Reblooming Iris which flowers in June and then offers a second crop of pristine white flowers in late summer. It’s hardy to Zone 4.
    • Other rebloomers, hardy at least to Zone 4, are: ‘Feed Back’, a dark purple; ‘Earl of Essex’, also purple; and ‘I Do’, with white flowers.
    • If you live in Zone 5 or warmer, try ‘Jennifer Rebecca’, a mauve pink beauty.

bearded-iris-3385748_1920_0_full_width.jpg
Photo: Bearded Irises. Credit: Pixabay.

  • Siberian Irises, I. sibirica, also comes in a range of colors. They have a delicate beauty than the stately beared irises but are equally rugged.

siberian-schwertlilie-786445_1920_full_width.jpg
Photo: Siberian Irises. Credit: Pixabay.

  • The Japanese Iris, I. ensata, has huge, flat blooms that resemble tropical birds and they thrive around ponds.

japanese-iris-2403420_full_width.jpg
Photo: Japanese Iris. Credit: Pixabay.

Wit & Wisdom

  • The iris is depicted in the French royal standard fleur-de-lis and is also the symbol of Florence, Italy.
  • Oral root, taken from the dried roots of Iris ‘Florentia’, was considered a cure for blood and lung diseases, and teething babies were encouraged to gnaw on a “finger” of dried root for its natural fluoride.

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Reader Comments

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planting iris bulbs

Submitted by Douglas Maurer on July 27, 2021 - 2:32pm

please clear something up for me. I have read several places that state when plant iris bulbs, plant them about 4 inches deep. but other places i have read i am to plant iris bulbs with part of pulps exposed to the elements. Could you please clarify which one is right so I can plant mine correctly, please. Talking about bulb and not the rhizsome

planting iris bulbs

Submitted by Douglas Maurer on July 27, 2021 - 2:31pm

please clear something up for me. I have read several places that state when plant iris bulbs, plant them about 4 inches deep. but other places i have read i am to plant iris bulbs with part of pulps exposed to the elements. Could you please clarify which one is right so I can plant mine correctly, please. Talking about bulb and not the rhizsome

planting iris bulbs

Submitted by Douglas Maurer on July 27, 2021 - 2:31pm

please clear something up for me. I have read several places that state when plant iris bulbs, plant them about 4 inches deep. but other places i have read i am to plant iris bulbs with part of pulps exposed to the elements. Could you please clarify which one is right so I can plant mine correctly, please. Talking about bulb and not the rhizsome

planting iris bulbs

Submitted by Douglas Maurer on July 27, 2021 - 2:31pm

please clear something up for me. I have read several places that state when plant iris bulbs, plant them about 4 inches deep. but other places i have read i am to plant iris bulbs with part of pulps exposed to the elements. Could you please clarify which one is right so I can plant mine correctly, please. Talking about bulb and not the rhizsome

planting iris bulbs

Submitted by Douglas Maurer on July 27, 2021 - 2:31pm

please clear something up for me. I have read several places that state when plant iris bulbs, plant them about 4 inches deep. but other places i have read i am to plant iris bulbs with part of pulps exposed to the elements. Could you please clarify which one is right so I can plant mine correctly, please. Talking about bulb and not the rhizsome

Iris

Submitted by Jeannine Ferrara on June 23, 2021 - 1:09pm

I live in Northwest Arkansas. My Iris leaves have yellow/brown spots on them. What is it and what can I do to prevent it?

2 different colors

Submitted by Lex on June 19, 2021 - 3:26pm

We have had a purple patch of iris’s for 6 yrs now. This is the first year that one of them bloomed and has yellow flower with purple outer petals, and see 2 more buds that look like they are going to be yellow as well. Is this common? Thank you

2 different colors

Submitted by Lex on June 19, 2021 - 3:26pm

We have had a purple patch of iris’s for 6 yrs now. This is the first year that one of them bloomed and has yellow flower with purple outer petals, and see 2 more buds that look like they are going to be yellow as well. Is this common? Thank you

Leaves on Iris turning brown

Submitted by Kathy on June 10, 2021 - 9:20pm

My Iris plants have been in a particular area of the yard for 15 years and always bloom large yellow flowers year after year. This year I noticed I barely had any blooms. In addition, some leaves are brown and slide right out of the root with no effort. The remaining leaves look unhealthy and not a vibrant green as in years past. At first I thought it might be cicada related, but have since thought otherwise. These are beautiful flowers and I fear losing them. What are steps I can take to begin assessing the cause and save the plants?

The big green “hip” on flower end after blooming

Submitted by Paul Wilson on June 5, 2021 - 9:26am

What is it, can you plant it? Is it good for anything?

Iris

Submitted by Kay on May 24, 2021 - 7:36am

I planted some very tall iris in full bloom in late spring. Should I cut them down and how far?

pruning irises

The Editors's picture

Submitted by The Editors on May 25, 2021 - 4:50pm

From our friends at the cooperative extension in Connecticut: Individual flowers should be deadheaded, leaving any unopened buds on the stem. Spent blooms look soggy and unattractive and will form seed pods if left on their stems. Seed pods should be removed. When all the flowers have blossomed, cut the stalk down to where it emerges from the leaves. Do not remove green leaves as they provide nutrition for the plant but they can be cut back to the ground when they turn brown. Cut all foliage down to 1 to 2 inches after a killing frost in the fall and remove all debris from area. 

Iris color very drab

Submitted by Jerry on May 21, 2021 - 2:03pm

I transplanted a few purple and white irises from my mother's garden. They came up fine, but they came up a very drab brownish color. My mom's were always a beautiful bright white and purple color. Is my soil bad?

why irises change color

The Editors's picture

Submitted by The Editors on May 25, 2021 - 4:54pm

It is not likely that your soil is bad, and, for the record, iris colors will not change based on soil pH like hydrangeas will. What often happens is that one cultivar is tougher than the others and eventually takes over a bed.  Then the resulting color is all the dominant plants. One solution is to thin out the bed and replace with some of the other colors and they should be fine.

Curved iris stalks

Submitted by Janet on May 14, 2021 - 6:25am

This year, our dwarf iris stalks came up curved in all directions. Most of the blooms do not looks healthy. We just laid down lime. Is it possible that some of the lime sprayed into the iris bed? Thank you!

Irises have not bloomed

Submitted by Anita on May 13, 2021 - 4:12pm

My irises (I have purple/white bearded) bloomed last year. A lady in my church said they only bloom every 4 years. Please advise. So far, they have green stalks, but no blooms yet. I'm in NJ

why no blooms

The Editors's picture

Submitted by The Editors on May 25, 2021 - 5:01pm

Once again, our friends at the cooperative extension have an answer: There are several things that can cause this problem. The plants may be too crowded. As the irises grow, the clump begins to crowd itself and must be divided. Another possibility is that the surrounding landscape (trees and shrubs) may have grown and begun shading the irises. Fertilization with a fertilizer high in nitrogen will stimulate vegetative (non-flowering) growth rather than flowers. Lack of water in late winter and early spring may also prevent proper growth.

It may be a good idea to divide and replant your irises. Find a sunny location receiving at least 6 hours of direct sunlight each day. Prepare the planting site by digging the soil deeply to loosen compacted soil. As you are turning the soil, add amendments such as compost and a phosphate fertilizer. If you use a complete fertilizer that contains nitrogen, phosphorus and potassium, be sure to select one that has a high phosphorus content (the second number of three large numbers on the bag). You can also use superphosphate or colloidal phosphate. Both of these are sources of only phosphorus (no nitrogen of potassium) and will not “burn” the plants. If the site chosen is the existing site, remove the iris plants and store them in a shady location until you are ready to replant.

For specific advice for your locale, consult your cooperative extension; find it here: https://www.almanac.com/cooperative-extension-services

Dividing Irises

Submitted by Mike on May 13, 2021 - 2:01pm

A brief comment about my experience dividing irises - be careful, it's not easy! I seriously injured my shoulder and chest. No, that won't happen to everyone, of course, but some advice to use caution won't hurt, either. Digging them out wasn't too tough, but I attempted to divide them in a few different ways, seeing what worked best: a sharp knife, various trowels, shovel. It was during that process that I yanked something and the injury didn't really set in until the following day. So I continued on dividing, finally settling on a hand saw - this got through easily and I sure wish I'd started with it! After replanting, the following year I didn't get much growth or blooms - I have Siberian irises. Second year, a little improvement. This is the third year and they seem to be coming along well finally. Perhaps conditions here didn't encourage a quick regrowth but do be prepared to lose some luster after dividing. However, if you don't divide, eventually you won't get any blooms at all - or just a couple, so it has to be done. Fortunately, it's years between the necessity to divide!

"orris" root

Submitted by kathleen kirchoff on May 13, 2021 - 9:11am

I think auto correct may have changed the the name Orris Root to Oral in this excellent article. That is the rhizome root of the Florentine iris dried and ground into powder. I have used it as a fixative in potpourri making.
My Mom's name was Iris so they are a family tradition which spans several generations of gardeners.

Flag Irises

Submitted by Don Marks on May 13, 2021 - 9:02am

If you plant a fair sized pond planter with bare routed flag irises planted in gravel and placed in your pond they will clean the water and reduce the algae bloom in the pond to almost nothing. I'm not sure how available they are in America, here in Britain they grow wild. The only problem with them is if you have large fish (koi etc) they will drag the pot around by the roots coming through the holes. yo may have to tie them up.

Iris plant

Submitted by Beverly Brown on April 30, 2021 - 5:42pm

Can a Iris be rerooted and how please?. I love plants and this is one I've never planted.

Iris ?

Submitted by Mary on April 18, 2021 - 8:28pm

Do Iris bloom the first spring after planting in the Fall? Mine didn't bloom and someone said it takes two year.

Short blooms

Submitted by F. Hudson Miller on March 22, 2021 - 12:42pm

Suddenly, after several years of normal behavior some of our iris have begun to bloom only 2 or 3 inches off the dirt surface. We live on Southern California. Any thoughts on why this is happening?

short stalks/stems

The Editors's picture

Submitted by The Editors on March 22, 2021 - 1:55pm

This is a tough one—for us, that is. Apparently short stalks (stems) are not uncommon. Some people believe that the problem is cold weather related, soil NPK related, or soil pH releated.  You might get a better answer from folks in your area. May we suggest that you contact your local cooperative extension service. You can find it here https://www.almanac.com/cooperative-extension-services

 

What to do with old leaves left over from winter

Submitted by shyamala on March 13, 2021 - 12:31pm

Hi, it’s spring in Northeast US, and Im finally getting to prepping the garden for spring. I still have a lot of long leaves ( some green, some green&brown) left on my iris plants from last year. Should I cut them back now? I want to make sure the new plants come up with the best possible situation, am worried that I may interfere w new growth ( I see small leaves already coming up. Would appreciate any advice!!! Thanks.

Iris Leaves

The Editors's picture

Submitted by The Editors on March 15, 2021 - 3:59pm

At this point, you can leave most foliage alone. However, do prune out any leaves that appear damaged or diseased, as they may harbor disease and pests. 

Iris bulb planting

Submitted by Doris Niehoff on February 20, 2021 - 10:19am

I just ordered some iris bulbs. I need to plant them in the fall now?

Planting Time

The Editors's picture

Submitted by The Editors on March 15, 2021 - 3:57pm

Fall is the best time to plant iris rhizomes, but if you have them earlier, you can plant them earlier, too. 

Iris seed pods

Submitted by Carolyn on September 27, 2020 - 2:24pm

Will iris seed pods grow? If so how long does it take to produce flowers.

Iris bulbs

Submitted by Sarah Birmanns on September 12, 2020 - 2:08pm

Hi! I am completely new to gardening and flower planting. Bear with me. I was given two bags of iris bulbs from a local friend. I really don't know what to do with them. For right now I have read (here) to put them in bags with holes in a cool place with some soil around them? And then plant them soon? It is mid September so I guess now is good? Does one make an iris bed? Do you plant them among other flowers? Do can you put something decorative around them like stones or mulch to keep weeds down?
Thank you!!

Pages

Growing Irises

Botanical Name Iris spp.
Plant Type Flower
Sun Exposure Full Sun, Part Sun
Soil Type Any, Loamy, Sandy
Soil pH Slightly Acidic to Neutral
Bloom Time Spring, Summer
Flower Color Blue, Multicolor, Orange, Pink, Purple, Red, White, Yellow
Hardiness Zones 3, 4, 5, 6, 7, 8, 9
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