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Growing Irises
How to Plant, Grow, and Care for Irises
How to Plant, Grow, and Care for Irises
Pixabay
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.
There are some 300 species in the genus Iris. The most familiar irises are the tall (at least 28 inches) bearded irises (Iris germanica).
These distinctive six-petaled flowers have three outer hanging petals (called “falls”) and three inner upright petals (called “standards”).
Irises may be a “bearded” type or crested (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.
Most irises flower in early summer. Some—mostly bearded hybrids—are remontant, flowering 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
- Plant irises in mid- to late summer (July to September/October) 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 irises are best planted closer to the fall because they go dormant in June.
- 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.
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 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.
- 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.
- Separate these rhizomes from the mother with a sharp knife and discard of the mother, as it will no longer produce blooms.
- Inspect the rhizomes for any rotting tissue or other signs of disease, removing and discarding infected parts or entire unhealthy rhizomes.
- Trim the iris foliage down to 3 to 5 inches in height so that the plants can focus on establishing new roots.
- 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!
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.
Photo: Bearded Irises. Credit: Pixabay.
- Siberian Irises, I. sibiricaalso, also comes in a range of colors. They have a delicate beauty than the stately beared irises but are equally rugged.
Photo: Siberian Irises. Credit: Pixabay.
- The Japanese Iris, I. ensata, has huge, flat blooms that resemble tropical birds and they thrive around ponds.
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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Summer blooms?
I was surprised to read this..the iris in our front and back yards have been there for years. Prior owners planted. But they O N L Y bloom in spring, never summer. And the Elk and Deer do NOT EAT THEM!
gift of iris in late fall
Hi,
I received a nice gift of a bag of iris from a friend. These iris are sentimental because they came out of my mom's garden years ago, went to him then to me. Today it's cold and snowy. Should I keep the iris in a bag in the garage for the winter or get them into the ground when the snow goes away next week? Thanks for your help.
Over Winter Irises
Hi Larry,
It’s amazing how special plants can be shared and sometimes come back around again! At this point, it would be better to leave the irises in a bag that has a few holes in it (for air circulation) in the garage, or other similar place that is cool, dark, and dry. Plant the irises in the spring as early as you can for the best results. We hope this helps!
over winter irises
Thank you for your advice! Yes they are special. My mom was a Master Gardener and a perennial expert. When both she and my dad passed, we took 80 specimens from her garden and planted them at our house. Because she preceded my dad in death, her iris were mostly gone. Getting these iris back, via a friend of her's, is very special. I'll keep them as you direct and plant them this coming spring.
Finding Iris too late to plant?
Could I plant in pots and bring in the house, and move later to greenhouse and than outside?
Iris's - General
I am caring for a very large garden with numerous varieties of everything including iris's - my primary question today is can all iris's stay in ground thru the winter?
Wintering irises
Sheila, I was just reading that “heaving” is a concern for wintering:
“In areas with very cold winters, Irises may benefit from being planted more deeply, making them less susceptible to heaving during freeze-thaw cycles.”
(The Almanac wont allow me to post a link, but it is from the latest blog entry at the American Iris Society’s web page.)
But root rot also seems to be a concern, so not too deep!
Happy gardening!
Invasive iris
We live beside Okanagan Lake. A 'clump' of yellow iris with very tall leaves in the yard (mostly sand) is making me nuts! we thought we dug them all out this spring..... but they are back with a vengence & spreading into my new shrubs! They are very deep in the ground & seem to be quite invasive. They look like the Siberian Iris, but are more foliage than flowers. What can I do to get rid of them?
Iris's - General
Here's my next question - is it too late to separate my clump. These have been so neglected for so long, one of the current 'clumps' is probably 2' square! Is it too late in the season to dig this up, take care of it, and replant?
Separating Irises
No, it’s certainly not too late to dig up and separate irises! The cool fall weather is ideal.
Iris
Hi, my Iris's after blooming had an eggy shape thing come out of the flower died, can you tell me what that is,,,thank you
egg shaped growth
That is a seed pod!
Iris
Something is eating my leaves of my Iris. What can I put on them?
Iris borer
It might be an iris borer. This can only be controlled by sanitation and the timely application of insecticides. Remove and destroy dead iris foliage in late fall or early spring. This will eliminate many of the iris borer eggs. An insecticide should be applied in spring when the new shoots are 4 to 6 inches tall. An application of an insecticide at this time should destroy small iris borer larvae before they have the opportunity to bore into the iris foliage. Speak to your local cooperative extension or garden center about treatments approved in your area.
Iris
Thanks for your timely iris information.
Iris and weeds
How do I keep grass and weeds from growing in my iris bed?
Weed Control in Iris Beds
Yes, weeds can be challenging in iris beds! Annual grasses, such as crabgrass and foxtail, can be controlled by hand pulling.
But perennial grasses, such as quackgrass, are much more difficult to control as they spread via underground stems or rhizomes. One option is to dig up the irises in July or August and replant them in a different (weed-free) location. Another option is to dig up the irises in July or August, set the irises in a shady location, and then dig up the grass and carefully remove the rhizomes and other plant parts. Dig up the area 2 or 3 times over a 3 to 4 week period, each time removing any rhizomes visible in the soil. Replant the irises in their original location after thorough eradication efforts. Quackgrass cannot be controlled by hand pulling. Herbicides are not a practical control measure for home gardeners.
Mulch is helpful in preventing weed growth, but it should be used sparingly (no greater than a 2-inch layer) to avoid disease problems. There are many herbicides labeled for use on irises.
weeds in iris bed
Can I spray the entire bed with a product like weed be gone to solve the problem
Soil for Iris
Planning to split and spread Irises - how should I prepare soil in new location? Thanks
Soil for Iris
Please see the “Planting” section, above!
After the bloom ...
Hi, i enjoy my irises each year and have had them in my yard since my mother planted them when I was a child. I'm now 68. They were transplanted just once from one side of the yard to the other. Beautiful each year. My question is this: after the flower wilts away there is a "bud" on the stem. What is this bud? Is it a seed to plant. If so I would like to plant them elsewhere ... look forward to your reply.
Iris Seeds
A seed pod will develop after the flower—however, you’d be much better off transplanting a couple of the existing rhizomes to another area. The seeds will take a long time to produce blooming plants, whereas the rhizomes should bloom in a year or two.
Irises Dug Up
Our gas company is working on gas lines and dig up an entire bed of our irises. I transplanted them in another location, but what else can I do to ensure their health?
Transplanting Irises
Irises transplant fairly easily; in fact, the general guideline is to “thin” irises every 3 or so years by digging them up, dividing them, and replanting.
It’s hard for us to answer your question because the main issues in transplanting are timing (September) as well as how you prepare the beds and plants. That part is done.
Here’s what you should have done: https://aggie-horticulture.tamu.edu/archives/parsons/flowers/iris.html
At this point, we hope the planting went well. Just avoid over-watering; irises hate wet feet and they will rot if water logged.
Unopened flowers
Something is eating my buds before they open. HELP!
Iris bud eaters
Are you sitting down? This is not pretty. Your iris are the victims of a small white Orthacheta Bud Fly maggot that bores into the side of the bud and eats the pollen inside. We’ll let the cooperative extension service explain further: When you see a small hole in the side of a bud or a disfigured blossom, remove it and check the stem. If there is no sign of passage, then you have it. Carefully break the bud or blossom apart, look for the maggot and destroy it. You can also put them into a zip lock bag for destruction. If the stem shows sign of passage, then the maggot has gone down the stem to change into the fly. Another good way to control an out break of the Orthacheta Bud Fly is to spray with a systemic when the buds have formed, this can be done when spraying for iris borers. Consult a local nursery for the proper systemic.
Iris stalks falling over
We have several beds of irises, and each year when they bloom, some fall over and lay on the ground. What do we need to prevent this happening?
falling irises
It turns out that there may be several reasons for irises falling over:
• the rhizome or toe of the plant may be deep enough
• the rhizomes may need to be divided (do it at the end of July or beginning of August)
• they may be in the shade and be reaching for sunshine, on weak stems due to lack of sunshine
• they may be over fertilized with a high-nitrogen product
• if none of those ideas apply, you can brace the plants with purchased metal supports (similar to tomato or peony cages) with one steel/metal stem support and a loop (to encircle the flower) at the top.
Pests
I have heard that critters can dig up bulbs for food. Is there anything I can do to lessen the possibility until my flowers are established?
Voles eating iris bulbs - how to prevent or greatly discourage
I am piggybacking to Frankie's question on 5/16/19 about iris-bulb-eating critters (animals). This is a serious problem in my iris garden where voles are the culprits. Below ground, they gnaw off the bottoms of the bulbs. A cat would certainly help, but the cat option is not a possibility for me. What are some ways to keep the voles from the iris?
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