Iris leaves turning yellow

How to Grow Bearded Iris for a Garden Full of Color

It’s a magical time when bearded iris flowers unfurl their pencil-slim buds to reveal a kaleidoscope of color, beginning as early as March in warmer regions. Depending on the type of bearded iris, they can be in bloom all the way into June. Some types even rebloom in late summer and fall. These hardy perennials flourish in USDA Zones 3-9, where winter temperatures dip below freezing and allow the plant to go dormant before next year’s growth.

“Anyone can grow iris,” says Doris Winton, who has had a lifelong attraction to this plant and is a master judge for the American Iris Society. It’s easy to understand why people have such passion for iris—it’s a very diverse group of plants, with bearded iris being one of three main categories. This kind of iris is so named because of a patch of soft bristles on the lower petals of the flowers. In addition to their long bloom time, bearded iris come in an incredible variety of colors and patterns. “Every color—except fire-engine red—can be found in bearded iris,” Doris says.

No matter which varieties you choose to grow, there are a few things you can do to help them thrive in your garden.

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Iris Growing Tips

  • Plant them in a sunny spot in late summer. The plants need well-drained soil and at least six hours of sunlight per day. A full day of sun is even better to keep the rhizomes dry. (The rhizomes are the fleshy rootlike structures at the base of the plant.)
  • Prepare their beds. Use a low-nitrogen fertilizer and apply it twice a year—in early spring and just after bloom when the rhizomes are forming the next year’s flowers. Water only if it is extremely dry or after transplanting.
  • Give them room to breathe. Bearded iris require good air circulation. Plant them a minimum of 16 to 18 inches apart (less space for dwarf irises and more for tall bearded iris varieties).
  • Do not mulch. Mulching retains moisture, and too much moisture will cause the rhizomes to rot.
  • Remove seedpods that form after the blooms have faded. This prevents seedlings from choking the surrounding soil. Seed formation also saps energy needed by the rhizomes, roots, and leaves.
  • Prune back the foliage in the fall. This will reduce the chances of overwintering pests and diseases.
  • Make dividing a habit. Divide clumps of bearded iris plants every three to four years in late summer.

Buy It: Tall Bearded Iris, from $14, White Flower Farm

How to Divide Bearded Iris

Bearded iris grow from a thick, rootlike structure called a rhizome. As the plant matures, the rhizome produces more rhizomes, which in turn lead to more leaves and flowers. Over time, however, the original rhizome withers and dies off. When this happens, bloom production slows and it is necessary to divide the plant, removing and replanting the newer rhizomes so they have the space they need to fully develop.

Step-by-Step Directions

Bearded iris should be divided in the late summer when the weather starts to cool. The division process illustrated below can be used for other plants that produce rhizomes, including canna, bergenia, dahlia, toad lily, and lily-of-the-valley.

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Step 1: Dig Up Clumps

Carefully dig the clumps with a garden fork or spade, taking care not to chop into the rhizomes more than necessary.

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Step 2: Break Apart Rhizomes

Divide the rhizomes by pulling them apart with your hands. In some cases, you may need to use a sharp knife to separate the smaller rhizomes from the main one. If so, dip your knife into a 10-percent bleach/water solution between cuts so you don’t spread any diseases to new rhizomes.

A good rhizome will be about as thick as your thumb, have healthy roots, and have one or two leaf fans. Large, old rhizomes that have no leaf fans can be tossed out.

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Step 3: Rinse and Evaluate Rhizomes

Wash the soil off the rhizomes to that you can inspect each one for iris borer (a plump, white worm). If you find a borer, destroy it. Some gardeners like to wash their iris rhizomes in a 10-percent bleach solution to protect against disease, but that won’t help plants that are already rotting. Make sure to discard any soft, smelly rhizomes you find, as well as any that feel lightweight or hollow, or appear dead, like the rhizome shown above.

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Step 4: Cut Leaves

Clip off the leaf blades so that they’re 4 to 6 inches long. This reduces the stress that the plant goes through as it concentrates on regrowing new roots instead of trying to maintain long leaves.

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Step 5: Plant Divisions

Replant divisions, setting the rhizome higher in the planting hole than the fine roots, which should be fanned out. A bit of the top surface of the rhizome should be just visible at the soil surface.

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Step 6: Plant Remaining Rhizomes and Water

Space the plants 12 to 18 inches apart (closer for dwarf varieties, farther apart for the largest). For the best display, plant the rhizomes so the fan of leaves face the same direction. Water well when planting bearded iris rhizomes, but do not continue to water unless the weather becomes dry.

Image zoom ‘Fringe of Gold’ bearded iris

Great Bearded Iris Varieties

Iris flowers have three primary structures, and descriptions of a variety often refer to these parts. For example, in the ‘Fringe of Gold’ flower shown above, the drooping “falls” are white-edged (or picoteed) in yellow. The upright “standards” are solid yellow. And the tiny fuzzy “beard” in the middle is white and yellow. You can use these structure names to imagine how an iris might look when you have only a text description.

As a longtime lover of bearded iris, Doris Winton has many favorite varieties, including ‘Fringe of Gold’. See below for several more of her favorites.

Image zoom This variety is a dwarf tall bearded iris with yellow blooms. The petals have a white and deep purple veined pattern that makes for a bold contrast on each bloom. Plant these irises in full sun. Zones 3-8

‘Bumblebee Deelite’ Dwarf Bearded Iris

This variety is a dwarf tall bearded iris with yellow blooms. The petals have a white and deep purple-veined pattern that makes for a bold contrast on each bloom. Plant these irises in full sun. Zones 3-8

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‘Rebecca Perret’ Bearded Iris

White petals fade into light purple on the tips on this softer bearded iris variety. The mid-height selection can thrive in full to part sun. Zones 3-8

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‘Perfect Pitch’ Bearded Iris

‘Perfect Pitch’ is a true purple bearded iris that has ruffled petals. This cultivar does best in full sun and is considered a tall variety. Zones 3-8

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‘Ozark Dream’ Dwarf Bearded Iris

If you love purple, ‘Ozark Dream’ is the bearded iris for you. The top petals of the bloom are a light purple, while the falls are dark violet. Plant this cultivar in full sun. Zones 3-8

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‘Latin Hideaway’ Bearded Iris

This tall bearded iris variety has a large contrast between the top petals (which are white) and the falls (in a brick red hue). The red falls petals have a hint of magenta near the center, and the inside of the white petals has a light pink hue. Zones 3-8

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‘Gallant Moment’ Bearded Iris

The scarlet blooms of this bearded iris variety make it stand out in the garden. The petals fade into orange and gold tones toward the center of the bloom. The outer edges of the petals become such a dark red that they almost look chocolate brown in places. Zones 3-8

  • By BH&G Garden Editors


While attending the Collin County Master Gardeners Show this month I found the most wonderful vendor called Ozark Iris Gardens. Owned by two brothers who have turned their iris hobby into a business. They grow and sell unique and rare irises from their Ozark, Arkansas farm.

After purchasing several varieties from them, they provided me the most wonderful iris growing guide. Today I am sharing this guide with you all since the brothers were very kind in giving me permission to share their tips and tricks with you.

Honestly, I am still learning about irises myself, but I do have several varieties that I have collected from friends and family. They are just such an easy plant to share and transplant and I am constantly hearing about people who have irises that have been passed down from previous generations. I also know that they are super hardy since we even have some planted by our mailbox which go pretty neglected for most of the year.

Checkout this small sampling from Ozark Irises. Aren’t these just insanely gorgeous!

Planting
    • Plant on a mound or raised bed in well drained soil. Most iris varieties do not like to be in moist conditions as rot can set in. Make sure the plant will get at least 6 hours of sun for the best blooms.
    • An iris root is a called a rhizome and looks somewhat like a potato. A common mistake is to plant too deeply. For best growth and flowering conditions, plant the rhizome with the top fourth of the rhizome above the soil exposed to the sun. Check this great example below where the owner showed me how to plant the bulb. His hand is to represent the soil level on the bulb when planting.

The owner of Ozark Iris Gardens shows me how far to plant the rhizomes by using his hand to represent the soil level.

  • As irises grow, they grow outwardly to the side and the back of the plant, so don’t plant too close to the side or the back of a flower bed as it will soon crowd the borders as it grows. A good rule is 12 inches apart, but we like very full beds for the best show of blooms, so we often plant only 6 inches apart.
  • Since the rhizome likes to be exposed to the sun, we do not use mulch. Mulch can also create moist conditions around the rhizome and not let enough air circulation around the plant, which can cause rotting. If the rhizome gets mushy, that is a condition called rot, which will kill the plant. If you must use mulch, try to keep it off the rhizome and away from the plant.
  • If there is no rain in the forecast, water the iris after planting. Irises don’t need a lot of water and usually the rain is enough. Be careful not to over water.
  • It is best to plant in the late Summer to early Fall. If planted too close to winter, the plant could get frost heave where the plant comes out of the ground. This happens because the roots have not had time to become established before the freeze.
  • And lastly, don’t expect blooms in the first year of planting. Usually the second year is great for blooms and the third year is awesome.
Fertilizing
  • Irises do not like a lot of Nitrogen. Too much Nitrogen can lead to rot. Most fertilizer blends have too much Nitrogen. Ensure the Nitrogen in the blend is 6 or less.
  • Irises do need a good dose of phosphate and potassium. A good blend is 6-23-18.
  • Fertilize after planting.
  • Fertilize twice a year, once before Spring and once in early Fall.
  • A broadcaster is great to use and gives just the right amount when walking slowly along the flower bed and broadcasting as you go

Checkout their special iris fertilizer on their website.

General Care
  • Irises do not need a lot of care. After bloom season is over, and if you are not hybridizing seeds, it is a good idea to cut off the bloom stalks close to the rhizomer for 2 reasons. First, as the bloom stalk dies back it begins to rot. If it doesn’t dry up completely, then the rot could get to the rhizome and cause some die out. Second, and a most amazing thing about iris seed pods is that each seed in the pod can be a completely different flower, so if you want to maintain the same flower in your bed, do not let the seed pod grow and drop seeds in the bed.
  • It is best to not cut off the iris leaves. The purpose of the leaves is for photosynthesis, so if the leaf is cut off, it is depriving the plant of nutrients. If the leaf turns brown or dries up, you can cut off the brown part or easily pull off the dried leaf. Some irises die completely back for the winter and the leaves turn brown and dry up. Just pull them off and new growth will appear in the Spring.
  • Irises do like to be transplanted when they become overgrown. A good indication for the need to be transplanted is when the clump does not bloom well after a few good bloom seasons. For Tall Bearded Iris, this can be every 5-7 years and for smaller varieties it can be sooner.
  • To transplant, dig up the clump. Some of the rhizomes will be long because a rhizome will grow a new length or nodule each year. Simply snap these apart and separate the clump into individual plants. You may end up with several extra rhizomes with no leaves on them. These are called mother rhizomes and are spent rhizomes that have already bloomed and had new growth in the past. These are usually thrown out. We like to seperate these from the plant and replant these, as we find that they will get new growth after being regenerated by the pruning.
  • Trim the leaves before replanting. This helps the plants stand up until the roots can re-establish in the ground.

Here are some neat shots of Ozark Iris farm. I would be in heaven if I had that incredible field of irises.

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Pests
  • The deer do not like the taste of Iris leaves.
  • An iris borer is a pest that comes from moth eggs. It will eat into the leaf and bore down to the rhizome. The infected leaves will rot and cause mush in the rhizome at the base of the leaf. This can be very destructive to an entire iris bed. Although we don’t like using pesticides, the best defense against borer caterpillars that have already hatched is a pesticide. Spray it on the leaves of the affected plant and those nearby. If you have a bad infestation, it is a good idea to burn the bed in late Winter (February) and clean out old leaves and get rid of any eggs. The burning does not kill the iris plant. The eggs are laid on the iris leaves, so a clean bed in the Fall where all the old leaves are cleared out is a natural defensive step.
  • Crickets like to eat small holes in the rhizomes. This doesn’t typically kill the plant, but does do some damage to the rhizome, which leaves it more susceptible to diseases like rot.
Louisiana Iris (much the same with the following exceptions)
  • Plant the root an inch under the ground, covered completely, but not too deep.
  • Louisiana Irises are more of a water plant and like to be near water, in ditches, and watered more frequently.
  • Mulch as much as needed. Pine needles are great for mulching.

I hope you have all found these tips helpful. I am so thankful that the guys at Ozark Irises allowed me to share all of their hard earned secrets.

I would also love to see what everyone has growing in their gardens. Feel free to send in pictures of your irises.

-Denise

Rhizome Plant Stock Photos and Images

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  • Purple nutsedge (Cyperus rotundus) seedling plants one with swollen rhizome forming
  • Ginger (Zingiber officinale) rhizome on a rustic wooden surface
  • Pale blue Bearded Iris (Iris Germanica) in full bloom in a garden close-up.
  • Pods of Canna, an agricultural rhizome plant which is the richest starch source in the world.
  • Ginger (Zingiber officinale) rhizome on a rustic wooden surface
  • Ginger (Zingiber officinale) is a flowering plant whose rhizome, ginger root or simply ginger, is widely used as a spice or a folk medicine
  • The pretty aromatic rhizome, Cucurma aromatica, which grows in hot, dry valleys.
  • Ginger (Zingiber officinale) rhizome on a rustic wooden surface
  • young plant calamus with root on white background
  • Siam Tulips, medical plant, medical plants, medicinal plant, medicinal plants, herbalism, useful plant, useful plants, homeopathy, traditional medicine, folk medicine (Curcuma longa, Curcuma rhizoma), rhizome
  • Ginger (Zingiber officinale) rhizome on a rustic wooden surface
  • fresh horseradish root on kitchen table
  • Iris sibirica – siberian iris
  • Ginger (Zingiber officinale) rhizome on a rustic wooden surface
  • Golden ginger rhizome or edible underground stems of Zingiber officinale
  • Spice, ginger, rhizome, spice plant, medicinal plants, fragrantly, tropical, exotic, Asian, Rhizom, ingredient,
  • Bearded Iris grows from a rhizome and is adapted to all climate zones. Blooms in spring. Northern California.
  • Red Canna Flower with Purple Foliage in Royal Botanic Garden Sydney New South Wales Australia
  • Small leaves of common bracken with one beautiful rhizome , the plant is also called pteridium aquilinum or eagle fern ,the background is green and
  • Geranium Rhizome small bush flowering purple blossoms
  • Sansevieria trifasciata or snake plant
  • Dark blue large bearded iris flower in a herbaceous border close up.
  • Flowering Turmeric (Curcuma longa) The rhizome (root) of this plant is used to make a culinary spice.
  • Fresh horseradish roots on wooden background
  • Ginger (Zingiber officinale) is a flowering plant whose rhizome, ginger root or simply ginger, is widely used as a spice or a folk medicine
  • Double flower of the unusual variety of the yellow wood anemone, Anemone ranunculoides ‘Fuchs Traum’
  • Yellow nutsedge (Cyperus esculentus) young plant
  • young plant calamus with root on white background
  • European lily-of-the-valley (Convallaria majalis), rhizome wth two leaves, Germany
  • Ginger Zingiber officinale rhizome
  • fresh horseradish root on old wooden table
  • Kohleria rhizome ready for planting with ‘measuring scale’ to aid size recognition
  • Closeup of a fresh ginger root, isolated on white background
  • Versatile ginger rhizome used as spice, medicine, candy and cosmetics
  • healing plants: Primrose (primula vulgaris) Whole plant on white background
  • The large, luscious foliage of Canna indica originating from single stems is dark green with purple-red markings, giving this plant a tropical feel.
  • A Red Upright Flowering Ginger Plant in Bloom in Singapore Botanic Gardens Republic of Singapore Asia
  • Transplantation of iris rhizomes, step 5, every part of the rhizome should have at least a stem with leaves
  • Raindrops on leaves of Colocasia plant
  • Macro detail of a fresh ginger rhizome.
  • Dark blue large bearded iris flowers in a herbaceous border close up.
  • Garden plant radish is isolated on a white background
  • Fresh ginger root or rhizome isolated on white background cutout
  • Canna Pods. Canna is an agricultural plant with the richest starch source. The plant grows from swollen underground stems.
  • Double flower of the unusual variety of the yellow wood anemone, Anemone ranunculoides ‘Fuchs Traum’
  • Young stinging nettle, Urtica dioica, shoots arising from a fragmented rhizome root in a flower bed, September
  • young plant calamus with root on white background
  • An uprooted Turmeric plant – roots and all – showing the different parts of the plant. The rhizome is wet from washing, and the background is black.
  • Ginger Zingiber officinale rhizome
  • fresh horseradish root on old wooden table
  • Close up of sliced fresh ginger root spice on wooden table
  • Closeup of a fresh ginger root, isolated on white background
  • Ginger (Zingiber officinale), rhizome, studio picture
  • Ginger roots in wooden bowl. Fresh rhizomes of Zingiber officinale, used as a spice or a folk medicine. Isolated macro food photo close up from above.
  • Rural Indian village woman holding Dried Turmeric roots / rhizomes in her hands. Andhra Pradesh, India
  • Canna Pink Sunburst
  • Transplantation of iris rhizomes, step 2, remove the soil around the rhizome, taking care not to damage
  • Raindrops on leaves of Colocasia plant
  • A ginger rhizome on top of a bamboo mat.
  • Wood-sorrel clump in Scottish woodland
  • Cypripedium Kentucky Pink Blush
  • Fresh ginger root or rhizome isolated on white background cutout
  • Cultivation of ginger plant (Zingiber officinale), Zanzibar Archipelago, Tanzania
  • Orange summer flowers of the half-hardy exotic garden plant, Canna ‘Oregon’
  • Lovebelts, root,
  • green leaf calamus with inflorescence on white background
  • Fresh ginger root over white background
  • ginger, isolated on white background, clipping path, full depth of field
  • fresh horseradish root on white background
  • Ginger roots isolated on a white background.
  • Close-up of piece and slices of fresh ginger root, isolated on white background.
  • Lesser Galangal, Chinese Ginger (Alpinia officinarum), rhizome, studio picture
  • Food background – Zingiber officinale or commonly know as ginger
  • Rhubarb plant (Rheum rhabarbarum) in blossom. flowering Rheum rhabarbarum in a vegetable garden
  • Bearded Iris, Iridaceae, purple flower, close up shot showing 2 tones of petal colour and yellow stamens.
  • Ginger is the rhizome of the plant Zingiber officinale, consumed whole as a delicacy, medicine, or spice.
  • Canna indica rhizomes.
  • Pacific Coast Iris (Iris innominata)
  • Root ginger (Zingiber officinalis) fresh rhizome isolated cutout cut out white background copy space
  • The rhizome of a yellow water-lily (Nuphar lutea), in a Jura lake (France). Rhizome de nénuphar jaune dans un lac Jurassien.
  • Fresh ginger root or rhizome isolated on white background cutout
  • Ginger rhizome (Zingiberaceae)
  • Orange summer flowers of the half-hardy exotic garden plant, Canna ‘Oregon’, against a white background
  • Planting of a Dahlia in a pot
  • green leaf calamus with inflorescence on white background
  • White lilies in a small lake.
  • Seed head of Arogrostus grass silhouteed against the dusk during the rainy season in Katavi National Park
  • fresh horseradish root on white background
  • Wasabi plant, rhizome and leaves on a white background
  • Green milkweed plant with a cluster of fresh flower buds.
  • Ginger (Zingiber officinale). A cup of tea with rhizome, studio picture.
  • Zanzibar, Tanzania; Turmeric rhizome growing at a spice farm on the island.
  • White isolated turf grass and earth. Rhizome
  • Ginger rhizome icon. Flavoring spices vector symbol.
  • A young lonely green fern plant growing in grass
  • Zantedeschia aethiopica rhizomes.
  • Turmeric (Curcuma longa) rhizome
  • Blue agapanthus plant in bloom
  • The rhizome of a yellow water lily (Nuphar lutea), in a Jura lake (France). Rhizome de nénuphar jaune dans un lac Jurassien.
  • Fresh ginger root or rhizome isolated on white background cutout

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Iris Root Rot: Preventing Rotting Iris Roots And Bulbs

Garden irises are hardy perennials and live a long time. They delight gardeners by blooming when the garden needs flowers, after the spring bulb blossoms have had their moment in the sun. Irises are easy-to-grow, graceful flowers that form the backbone of many a garden in this country, but they not entirely without problems. Iris root rot is one of them. Read on for information on root rot in iris and how to treat iris rot.

Root Rot in Iris

Root root in iris is also known as soft rot, and if your irises have ever had it, you know why. The leaves become soft, and the rhizome root grows mushy.

Iris root rot is a caused by Erwinia carotovora, a bacterial phytopathogen. It usually gets inside the rhizome through an opening created by some kind of injury. Any pest could provide this entry, including borers, slugs, snails,

beetle larvae or even rough use of tools.

With iris root rot, you’ll first see yellowing at the center of the fan of leaves. In time, the center turns brown and collapses. Root rot in iris always produces a mushy, bad smelling rhizome. Often, you’ll also see decay in the plant’s leaves.

Preventing Rotting Iris Roots

Iris root rot is not easy to cure. However, many times you can avoid it by using good cultural practices in your garden.

First, make sure that your irises are planted in sunny sites. Good soil drainage is critical, so consider raising your beds if need be to ensure proper drainage. Adequate spacing between rhizomes is also important since overcrowded plants are more vulnerable to bacterial growth.

Don’t plant your rhizomes too deep in the soil, and keep dirt from the base of the fans. Never use fresh manure on your iris plants, especially if drainage is a problem. Instead, feed your plants with gentle fertilizers.

How to Treat Iris Rot

If you want to know how to treat root rot, it means your irises are already under attack. You’ll need to dig up each diseased rhizome and inspect it carefully. If the iris root rot is extensive, destroy the iris rhizome. Unfortunately, this is the only method of root rot control in iris if the rot has spread.

You can learn how to treat root rot that is not so extensive, however. For less seriously affected plants, cut out and dispose of all parts of the rhizome that are diseased. Use sterilized tools to do this, and sterilize them again after use to prevent spreading the bacteria.

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Tuesday – April 22, 2008

From: pahrump, NV
Region: Rocky Mountain
Topic: Pruning, Herbs/Forbs
Title: Browning of leaf tops on Iris plants
Answered by: Barbara Medford

QUESTION:

My Iris plants bloomed beautifully, now some of the leaves are turning brown from the top down, about half way. Is this normal? What can I do about it and should I cut off the brown leaves? Also, what causes this?

ANSWER:

Irises are very tough and, unless you have borers in the rhizomes, it is okay for them to have some brown leaf tips. We always liked to trim them off below the browning with a sharp scissors or pruner, and at a diagonal. No particular reason, it just seemed more attractive that way. You need to leave as much healthy leaf as you can, as the leaves are the manufacturing facilities building up the root systems of the iris and preparing the rhizomes to expand and give you more blooms next year. In the Fall, you can trim off all the leaves the same way, in a fan, about 4 to 5 inches above the root system. Clean out any dead litter around the rhizomes to help prevent disease or mold. See this page of Images of iris care. Some of the images can be clicked on for more information.

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Why Are My Iris Yellowing And Dying?

Answer #1 · Gardenality.com’s Answer · Hi Mary,
Sounds like your Iris plants either have a disease or have Iris Borers.
If it’s a disease it sounds most like bacterial soft rot. This disease is perhaps the most common found in Irises. The disease usually finds its way in by entering small holes made by Iris Borers, or through other damaged areas of the foliage. The symptoms are slow dying and yellowing of the leaves starting from the top of the foliage, and a soft greenish yellow or brown decay at the base of the foliage. This rot slowly moves to all of the rhizomes…roots.
The only method of control for bacterial soft rot is to catch it early. If spots and/or yellowing leaves are present immediately remove, selectively, those leaves. If the disease has reached the rhizomes at and below the ground level, remove the entire plant and all of it’s rhizomes/ root system and discard.
Iris Borers enter the rhizomes and slowly eat them away. The only way to check for these borers is to dig up the rhizomes and inspect them. If holes in the rhizome(s) are present then you will want to break open them open. If you see the nasty slimy critters inside you’ll need to remove all rhizomes that they inhabit. You can save and re-plant the rhizomes that have no borers present.
If you find neither borers or disease try fertilization with a high content of phosphorus. Phosphorus is the middle number in the three number analysis on most fertilizers. Example:10-10-10. The middle number is phosphorus. Many flower foods contain a high amount of phosphorus. Phosphorus promotes rapid root development in turn producing more foliage, more buds, and more blooms. Sounds like maybe your Irises need some of that. You could also get some Triple Super Phosphate (0-46-0) if you can’t find any other high phosphorus fertilizer. If you don’t understand what I’m referring to stop by your local independent nursery and they should be able to hook you up with the right fertilizer product(s).
Hope this helps you.
Brooks Wilson))

Iris, Rhizomatous (Iris spp.)-Bacterial Soft Rot

See:

Calla Lily (Zantedeschia spp.)-Soft Rot

Cause The bacterium Pectobacterium carotovorum attacks several hosts including calla lily, iris, and dahlia. The organism is in most cultivated soils and regularly overwinters in soil. Bacterial soft rot can attack plants any time of the year but often is noticed in the critical months before bloom. The organism enters through wounds. Seedlings sometimes suffer at the beginning of their second year, and so do established plants that have stayed too long in one place and become congested. The disease has also been associated with contaminated surface waters used for overhead irrigation.

Symptoms Yellowing or browning of leaves, especially the fan’s outer leaves, is an early symptom, resulting from a soft decay of the leaf base or of the rhizome itself. Water-soaked streaks on the leaf blades, progressing upward from the base of the leaf fans, are another initial symptom. Rhizomes become rotted and may be foul smelling. Eventually, leaves become dry and brownish-gray and tops die. When infected plants are lifted for dividing, often-empty shells are all that remain of the rhizomes.

Cultural control

  • Destroy all infected plants and rhizomes.
  • Avoid wounding rhizomes when digging.
  • Dry rhizomes in sun and replant in a new well-drained site.
  • Plant shallowly to expose part of rhizome to the sun.
  • Divide plants frequently enough to avoid serious congestion.
  • Use well water or disinfected surface water for irrigation.

Chemical control Combine with cultural control methods because chemical control is difficult and often ineffective.

  • Phyton 27 at 1.5 to 2 oz/10 gal water. Group M1 fungicide. 48-hr reentry.

Reference Lacy, G.H., Lambe, R.C., and Berg, C.M. 1982. Iris soft rot caused by Erwinia chrysanthemi, associated with overhead irrigation and its control by chlorination. In Combined Proceedings International Plant Propagators’ Society 31:624-634.

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