Grow Bearded Iris | Bearded Iris Care (2024)

Fungal Leaf Spot: Fungal Leaf Spot, caused by the pathogen Didymellinamacrospora,is a common occurrence for all types of iris battling anunusually wet spring season. It primarily attacks the foliage, but may alsoinfect the stalk and buds. Fungal Leaf Spot may affect all species of iris, butbearded iris seem to be most susceptible. Fungal Leaf Spot can greatly reducethe vigor of an iris and may result in death if the disease is allowed toprogress year after year.

Signs & Symptoms: A few clues to help identify which pathogen may be affectingyour iris are to note the shape and color of the lesions on the infectedtissue. Fungal Leaf Spots are circular, or oval-shaped, first appearing as ⅛-¼”dark brown spots surrounded by a chlorotic water-soaked border. As the lesionsenlarge they will show a distinct brownish-red outline.

Disease Environment: Fungal Leaf Spot develops and thrives in conditions withconsistent moisture on the leaf surfaces, cool-mild temperatures, and poor aircirculation. It spreads by water, wind, and contaminated tools and equipmentnot properly sanitized after coming into contact with infected debris.

Cultural Prevention: Above all, we first encourage growers to establish strongcultural techniques for preventing environments susceptible to this disease.Preventive techniques include planting your iris with adequate spacing to allowample air circulation at approximately 12-24” apart and avoiding overheadirrigation as much as possible. Make sure neighboring plant foliage is notovercrowding your iris and keep up on the weeding! Plant your iris in locationswith full sun and ensure the soil has excellent drainage.

Control Measures: Sanitationis the next best measure to reduce disease progression. Remove and dispose ofup to ⅓ of infected foliage leaving some to remain to continue tophotosynthesize. We recommend removing all the diseased foliage in the Autumn.Doing so should significantly reduce the number of spores that can survive thedormant season. If the disease is developing at a rapid rate, you may apply afoliar fungicide at 7-10 day intervals to help protect new growth. Contact yourlocal garden center for their recommended fungicide options. Adding asurfactant such as ¼ tsp of Dr. Bronner’s castile soap per gallon will help thefungicide stick to the foliage. Be mindful of applications, timing them aroundthe rain so they don’t quickly wash off. Be sure to read your product labelcarefully noting environmental hazards and the advised PPE. Fungicideapplications are most successful when applied when the fans grow to 4-6” tall.

Iris need at least a half day of sun. In extremely hot climates, some shade is beneficial, but in most climates Iris do best with at least 6 hours a day of full sun. Without sufficient sun, the iris may "go blind" - producing foliage but no blossoms.

Soil Preparation:
Iris will thrive in most well-drained garden soils. Planting on a slope or in raised beds helps ensure good drainage. If your soil is heavy, coarse sand or humus may be added to improve drainage. Gypsum is an excellent soil conditioner that can improve most clay soils. The ideal pH is 6.8 (slightly acidic), but Iris are tolerant in this regard. To adjust the pH of your soil, lime may be added to acidic soils or sulfur to alkaline soils. It is always best to have your soil analyzed before taking corrective measures.

When, Where and How to Plant Bearded Iris Rhizomes:
For best results, Iris should be planted in July, August or September. It's imperative that the roots of newly planted Iris be well-established before the growing season ends. In areas with hot summers and mild winters, September or October planting may be preferred. We strongly suggest Iris be planted at least six weeks before the first hard frost in your area.

Iris should be planted so the tops of the rhizomes are exposed and the roots are spread out facing downward in the soil. In very light soils or in extremely hot climates, covering the rhizome with 1 inch of soil may be desirable. Firm the soil around each rhizome and then water to help settle the soil. A common mistake is to plant Bearded Iris too deeply.

Iris are generally planted 12 to 24 inches apart. Close planting gives an immediate effect, but closely planted Iris will need to be thinned often. Plants spaced further apart will need less frequent thinning.

Watch our video on how to plant bearded iris:

Bearded Iris range from the small to the tall, with the shortest of them beginning to bloom as early as late March here in Oregon. The color spectacle continues into April with the emergence of the Median Bearded Iris, followed by the Tall Bearded Iris which begin to fade in early to mid-June. Bloom time for each variety lasts approximately two weeks, depending on the weather.

There are some Tall Bearded Iris that bloom early and some that bloom late, so try some of each to lengthen your season by a week or two. Consider some of the smaller bearded Iris, such as the Intermediate and Standard Dwarf Bearded Iris, as you can add a month to the beginning of your bloom season using these. And finally, consider the reblooming Iris, which can give bloom in the summer and fall.

For Iris to bloom consistently, they need full sun, good drainage, lots of space, and quality soil. To improve your chances of bloom, add fertilizer and divide large clumps. Only 60-75% of Iris bloom the first year after planting. Sometimes they need an extra year to become established. Unusual weather conditions or late spring frosts can also harm Iris blooms.

Reblooming Iris:
Several varieties of Bearded Iris have been known to rebloom after the initial spring bloom season. These are known as Rebloomers. All categories of Bearded Iris from the Miniature Dwarf Bearded to the Tall Bearded have varieties that rebloom, usually 4-8 weeks after initial bloom. Subsequent blooms are not as reliable as the initial bloom, and depend greatly upon the quality of the soil, climate, and geographic location. Remontancy is not guaranteed. Check our online catalog for several varieties of rebloomers.

Floral Arranging with Iris:

For longer lasting flowers cut your Iris early in the day with the buds just opening. Place them in a bucket of tepid water and re-cut the stem end underwater at an angle one inch up. Display your Iris in a cool niche away from direct sun and drafts. Pinch off and remove wilted flowers immediately. Check the water level every day and replenish as needed.

Tip: Cut Iris tend to drip a sap-like substance. The drips from dark Iris can stain fabric and other surfaces. We suggest placing an underlay beneath the vase of Iris, or placing the vase on a non-porous surface.

Lack of bloom can be caused by a number of factors and usually a combination of more than one. They are a bit like people -- give them a bit of room and satisfactory conditions and they will perform well. Here is a list of some of the more common culprits:

• Planting in too much shade. They need at least 6 hours of full sun per day.
• Over feeding with animal manure or fertilizer high in Nitrogen. (We recommend a low-Nitrogen fertilizer, such as a 6-10-10 mix).
• No feeding at all. Starved Iris will not flower.
• Planting too deeply. Tops of rhizomes should be visible above the soil level. (In extremely hot areas of the country, cover tops of rhizomes with only about 1 inch of loose soil or sand to prevent sun scorching.)
• Mulching with lawn clippings or other organic matter. Don't mulch, as it acts as shade and can cause rhizomes to rot.
• Over or under watering can also cause problems. Plant Iris is well-drained soil. Water deeply once every week or two during the dry spring and summer months.
• Overcrowding: they need dividing every 3 to 5 years.

We sometimes have customers tell us that their entire patch of Iris changed from its original color to white or yellow. Iris cannot change color. Usually, when a customer notices this unusual occurrence, what has happened is that the purple (or red, or pink, or blue, or yellow, or black, or whatever color) Iris has grown into another nearby patch and the one color has dominated (or crowded out) the other. When dividing Iris in the summer, it is an easy mistake to make to throw out one color and plant the other in the entire bed.

Another culprit is weed killer. The use of herbicides, such as Roundup, near the Iris can affect the plants and cause flowers to go whiteish and contort. If they recover from the exposure to these chemicals, the original color will return in subsequent bloom seasons.

A third possibility is that bees have cross pollinated and a seed pod has developed. The seeds from these crosses can drop into the bed and grow and mature over time. Then one bloom season, a new Iris is found blooming in your Iris patch.

Newly set Iris plants need moisture to help their root systems become established. Specific watering information depends on your climate and your soil, but keep in mind that deep watering at long intervals is better than more frequent shallow waterings. Once established, Iris normally don't need to be watered except in arid areas. Over-watering is a common error.

Specific fertilizer recommendations depend on your soil type, but low-nitrogen fertilizers (6-10-10), bone meal, and superphosphate are all effective. A light application in the early spring when tulips are blooming in your neighborhood, and a second light application about a month after bloom will reward you with good growth and bloom. Avoid using anything high in nitrogen.

A concise read on the components of fertilizer by Joe Lamp'l on the blog "Growing a Greener World" summarizes nicely, "For promoting good fruit or flower production, look for a middle number that is higher than the first. Otherwise, your plants will be stimulated to put out lots of nice green foliage, likely at the expense of fruit or flower production. Instead, you want the energy and nutrition of the plant to go towards the desired result, flowers or fruit, so a higher middle number is a more appropriate choice." Read the full post.

Watch Ben Schreiner advise us on how to fertilize our iris:

Schreiner's Iris Gardens offers a specially formulated, low-Nitrogen Iris food.

Keep your Iris beds clean and free of weeds and debris, allowing the tops of the rhizomes to bask in the sun. Bloom stalks should be cut off close to the base after all buds have finished blooming. Healthy green leaves should be left undisturbed all summer, but diseased or brown leaves should be removed. In the fall, trim the leaves to a height of approximately six inches. Remove weeds, leaf debris, grass roots from Iris beds. In regions with especially cold winters, lay winter protection over the rhizomes. We recommend straw, evergreen boughs, or anything that will provide air circulation and insulation against the cold. Remove winter protection in the spring.

During bloom season, spent blooms, as well as spent branches, can be removed carefully to keep your Iris beds looking fresh and colorful.

Watch our short video on the proper way to remove spent blooms. Run time 1:18 minutes.

Here's another video on deadheading Iris from our friends at Garden Time.

Iris need to be thinned or divided before they become overcrowded, generally every 3-5 years. If Iris are allowed to become too crowded the bloom will suffer, some varieties may crowd others out and disease problems may be aggravated. Depending on your location, July through September is the time to divide and transplant Bearded Iris.

Transplanted Iris should be planted a minimum of six weeks before the first hard frost in your area.

Old clumps may be thinned by carefully cutting out the old divisions at the centers of the clumps and leaving new growth in the ground. In the case of very old and compacted clumps, the process of thinning might be easier if you dig up the entire clump, remove the old "spent" rhizomes, trim the foliage of the new rhizomes and replant them. Smaller shoots may take two years to produce blooms, but larger shoots should bloom the following spring.

We recommend supplementing the soil with a low-nitrogen fertilizer, super phosphate or bone meal when transplanting. These extra nutrients help the new shoots to have the best chance of success in establishing their root systems. Water newly planted rhizomes well initially, and if dry conditions continue then once every 7 to 10 days until the autumn rains begin, to help the new roots become established.

Is your Iris bed overgrown? Need saving? Read our blog post at WordPress for more tips and reassurance....

Watch Ben Schreiner's short tutorial on how to dig and divide bearded iris:

Controlling Rhizome Rot:
Excessive moisture can sometimes lead to outbreaks of bacterial rot. It is imperative that you remove the rotting tissue as soon as possible. Remove the soil from around the rhizome, leaving the roots anchoring the plant. Using an old spoon, carefully scoop out all the mushy tissue. If necessary, dig up the entire plant and remove the rotten tissue. After removing the tissue, drench the wounds with a 10% bleach solution (1 part bleach to 9 parts water) and allow them to dry for several days before covering with soil again.

Excessive moisture can sometimes lead to outbreaks of bacterial rot. It is imperative that you remove the rotting tissue as soon as possible. Remove the soil from around the rhizome, leaving the roots anchoring the plant. Using an old spoon, carefully scoop out all the mushy tissue. If necessary, dig up the entire plant and remove the rotten tissue. After removing the tissue, drench the wounds with a 10% bleach solution (1 part bleach to 9 parts water) and allow them to dry for several days before covering with soil again.

Iris Borer:
In areas where Borers live (we do not have Iris Borers here in the Western United States), they can pose serious and frustrating problems for the Iris grower. Borers begin life as eggs, laid on garden debris in the fall. Each spring, about the time tulips bloom, these eggs hatch into larvae.

These 1/4 inch long larvae crawl onto the Iris and up the leaves. Near the top they chew into the leaves and then down to the rhizomes, where they gorge themselves until they reach a size of about 1 1/2 inches in length. Borer injury often appears as notched wounds or slimy wet looking areas on the leaves. Borers often will hollow out whole rhizomes causing the fans to collapse and the remaining tissue to rot.

Keeping a clean garden is the fist step in minimizing Borer problems. A sharp eye for signs of Borer entry allows some gardeners to catch the Borer in the leaf before it travels to the rhizome (simply squash them in the leaves). The most effective control relies on an understanding of the Borer's life cycle.

Sometime in the summer the Borers change into pupae. These pupae reside in the soil for about a month and then a moth emerges and lays eggs. As pupae, moths and eggs, the Borers do not feed. Only as larvae do they eat and do their damage. At this stage they are most vulnerable to our efforts to control them.

Systemic insecticides are considered to be the most effective control of Iris Borers. Always take care to follow the manufacturer's recommendation when using agricultural chemicals. (Imidacloprid has proven effective against Iris Borers. Check with your local garden center about systemic insecticides that contain this chemical.)

A 10% solution of Murphy's Oil Soap (one part soap for every nine parts water) can be used as an organic alternative to commercial chemicals. Diatomaceous Earth is also effective in ridding plants of caterpillars. It shreds the inside of caterpillars when they ingest the dust, but you do have to reapply after a rain or watering as it loses its effectiveness when damp. Recent research has given us another organic approach to borer control. Read the article here on the use of nematodes to combat the Iris Borer.

Slugs, snails and other pests around Bearded Iris:

In early spring, or when you notice damage from slugs and snails, bait for these pests using whatever method you prefer. Aphids, thrips, and whiteflies can be controlled by a variety of insecticides readily available at garden centers. Insecticidal soaps can also be effective.

Aphids:

We suggest you make a homemade insecticidal soap, a low-toxicity bug control solution that will desiccate the soft bodies and kill the aphids without doing harm to your plants. Simply mix a few teaspoons of liquid dish soap with one quart of water, then spray or wipe the solution onto the leaves, stems, and buds of the plant. (Don’t forget: These bugs like to hide beneath leaves, so take care to thoroughly coat the underside of the leaves, too.) Repeat the process every two or three days for the next few weeks, until you no longer notice aphids on the plant.If your aphid infestation is not eliminated by the use of insecticidal soap, you may need to use a systemic pesticide. Consider using a product containing Imidacloprid. Mix and apply according to the manufacturer’s directions.

Love the idea of iris in containerson a sunny patio or balcony? Iris can be grown in containers with much success.Follow these simple steps:

Step1: Select a roomy pot.It needs good drainage, and it should be the final container for your springbloom. For Tall Bearded and Intermediates, use a one-gallon size at least. ForDwarf Iris a 6” to 8” pot will work.

Step2: Soil should bea good potting soil that drains well. You can use a general potting soil foundat most garden centers, but avoid potting soils high in Nitrogen.

Step3: Leave the soilat least one inch below the container’s rim, and be sure the top of yourrhizome is exposed. Water only when the top two inches of soil are dry, asoverwatering can cause rot.

Step4: Winter thecontainer outdoors. Sustained temperatures below 32F and overnight temperaturesbelow 25F will require protection to prevent the pot from freezing. Winterprotection can include moving pots into a garage for a short amount of time, orcovering pots with a freeze cloth cover that can be obtained at most gardencenters. The smaller the pot, the faster it will freeze. In northern climateswith harsh winters sink the pot into the soil and cover it with mulch.

Step5: Divide andtransplant your iris every couple of years to prevent them from crowding in thepot.

The practice of “Companion Planting”, a centuries-old gardening
tradition, grew from the proven notion that different plant species, planted
close together, assist each other with nutrient production and
absorption, controlling pests, attracting pollinators, and other factors
necessary for their full productivity. This practice is clearly
beneficial in flower gardens as well. When planning your companion plantings for Bearded Iris beds, consider
water conservation as well as overall aesthetic design.

Below are links to articles about companion planting specifically with Bearded Iris. We are confident that you will find inspiration and information on the potential for color in your garden.

Ideal Companion Plants for your Bearded Iris Gardens (Schreiner's Iris Gardens' WordPress blog post)

Tall Bearded Iris and Companion Plants (American Iris Society blog post)