9 Reasons Your Irises Aren’t Blooming This Season
Are your irises struggling to bloom in your garden this season? These lovely flowers make for a wonderful garden display each season, but can struggle to bloom for a variety of different reasons. In this article, certified master gardener Liz Jaros looks at why your irises aren't blooming, and how to address the issue.
Iris flowers are among the greatest pleasures of spring. When an iris is not blooming, it can be caused by improper planting, overcrowding, or unmet environmental needs. Determining the exact culprit can be a guessing game, but lucky for you, we’re here to help!
Let’s look at 9 of the most common reasons your iris isn’t blooming and propose solutions for nipping the problem in the bud.
First, The Joys & Confusions of Spring Flowers
Anticipation is one of the joys of gardening. Any day now, you expect a bouquet of iris flowers to open and fill the air with that sweet, familiar scent. The soft, ruffly petals will be breathtaking in shades of yellow, cream, and purple. The cutting garden will be ripe for the picking. The neighbors will pause on their walks to ask if you’ll share your secrets.
It’s been a long, gray winter, and spring was peppered with the delights of tulips, daffodils, and hyacinths. You’re ready for the parade of perennials! Up first is your beloved iris: Maybe it’s a Dutch variety that a fellow gardener shared with you at the end of last season or a Japanese cultivar you planted near the creek. It should bloom any day now. But let’s say it doesn’t.
Maybe you are scratching your head, looking at a plant with healthy leaves but zero flowers. Perhaps the leaves are brown or wilted, with no signs of floral growth. Maybe you’re looking at stems with no buds. And suddenly, it dawns on you that something has gone wrong.
Here are 9 possible causes for your plant’s startling lack of flowers.
It’s Newly Planted
Although an iris can be planted almost any time during the growing season (depending on your zone), the best time to plant is fall. This allows your iris to set strong roots, photosynthesize, and store the nutrients needed for healthy flowering next season.
With a fall planting, there’s a good chance you’ll see blooms next year, but not always. Some varieties will need more time to establish and may not bloom until the 2nd or even the 3rd year. Around 25 percent of irises planted at the perfect time in the perfect location under the perfect conditions will not bloom in their first full season. Be patient with them!
If you’ve planted a bulb or rhizome iris in late winter or early spring, which is doable in warmer climates, you probably won’t see flowers until the following year. Depending on the plants’ storage conditions, it may take a season or two to get on the same dormancy cycle as other perennials in your yard.
If you’ve planted a nursery-grown iris after the plant’s bloom time has expired, you’ll have missed the show and have to wait until next year. But again, it’ll be worth the wait. Hang in there!
It’s Planted Too Deep
Rhizomes or bulbs planted too deeply can pose issues for a developing iris. This is one of the most common reasons an iris is not blooming. These plants are not difficult to grow, but their planting instructions must be followed carefully, or flowering will be adversely affected.
For a rhizome iris, experts advise digging a hole 4 inches deep and mound up some dirt in the center. Set the rhizome (the fleshy, potato-like part) on the mound and let its root hairs drape down over the sides. Backfill lightly so that the rhizome sits just at surface level and is not completely covered with dirt.
For a bulb iris, dig a hole 6 inches deep and four inches wide. Plant your bulb with the pointed side up and the flat side (with the root hairs) growing down. Backfill loosely with the soil that was excavated from the hole.
The good news is, if you believe your irises are not flowering because they have been planted improperly, you can dig them up and plant them again using the proper depth. In all likelihood, they’ll flower just fine next year!
Irises need a lot of space. Not only do they require good airflow to prevent disease, but they also spread vigorously once established. So plant them 12-24 inches apart from the get-go, even if they’re just a small fan of leaves at the start. When they start to take off, you’ll be glad you did.
One of the most common causes of limited iris flower growth is overcrowding. Signs of overly dense plants include:
- Tight clumps of foliage
- Matted or buckling root clusters
- Aead zone in the middle of the plant where nothing grows
With most iris cultivars, you can expect overcrowding every 2-3 years. The plants direct most of their nutrients toward expansion, and newer roots will send up more flowers than the mother bulb or rhizome. Crowded plants should be dug up, divided, and replanted to encourage healthy roots and optimal flowering.
To divide a rhizome iris (German, Siberian, Japanese…), use a sharp knife to cut off the outer sections of the plant. Aim to include a large piece of rhizome (the potato part), some root hairs, and at least a small green bud or ‘fan’ of foliage.
To divide a bulb iris (Dutch, Dwarf…), use a sharp knife to cut off new bulblets that have grown from the mother bulb. Include a few shoots and roots with each bulblet for best propagating success.
It’s Not Getting Enough Sun
Most iris varieties, especially bearded cultivars, require a full 6 hours of sunlight daily to flower to their fullest potential. Some irises, particularly Japanese and Siberian cultivars, can handle a bit of dappled shade. But even these irises must get at least 4 hours of direct light per day.
An iris receiving too much shade may have firm, green foliage and an upright habit, but its flower production will be minimal. If you suspect your iris is not blooming due to low sunlight, consider relocating it or trimming nearby trees and shrubs that might be casting too much shade.
A plant conserving water will not send up as many blooms as one that’s well-hydrated. During drought, an iris will use whatever moisture is available to quench its roots and ensure its leaves can photosynthesize. If there’s nothing left over for nurturing flowers, it will stop producing them.
If your plant has dry, brown leaves or a wilted appearance, or the ground looks parched, evaluate your watering practices. A newly planted or transplanted iris needs regular, even watering (but not too much!) until it enters dormancy.
While an established iris does not need much supplemental water, it may need an extra drink here and there when rain/snow is scarce. Direct water at the roots rather than the leaves, and be extra vigilant when it is entering or leaving dormancy in early spring and late fall. This is when an iris is particularly active and may be thirsty.
It Has a Disease or Pest
A plant suffering from root rot may not flower well or at all. If its leaf fans are browning at the base or falling over, you may want to dig it up and investigate. Irises are highly susceptible to root rot, and that can have a major impact on bloom capacity.
Root rot can be caused by the introduction of bacteria by a boring insect or root damage or by a fungal condition fueled by an overzealous watering regimen. If an excavated iris has a few mushy rhizomes and some firm, healthy ones, cut the rotten ones away aggressively and remove some dirt from the area around it. Replant with some new dirt, and monitor carefully.
Similarly, if a bulb iris exhibits rotten roots, the mushy bulblets can be cut off, and the healthy sections replanted. If the entire plant seems soft, dispose of it and replace the dirt in the area.
Sap-sucking pests can also cause disease and stress that may reduce flower output. When insects like thrips or aphids pierce holes in the leaves or produce excrement that hinders photosynthesis, the plant will direct its energy toward foliage rather than flowers.
Keep an eye out for small holes or chew marks and a black, sticky residue on leaf surfaces to indicate insect damage. Diligent hand removal with a strong hose spray or applying horticultural oil can help prevent next year’s iris from losing blooms to sap suckers.
It Was Overfertilized
Fertilize irises with an NPK ratio of 6-10-10 to encourage abundant, healthy flower cycles. Excessive amounts of nitrogen will lead to foliage production rather than bloom production, so you want to ensure your iris is getting a mix of mostly phosphorus and potassium.
If you suspect improper fertilization as a possible culprit in your flower failure, but you applied the correct NPK ratio, ensure the iris isn’t receiving incidental nitrogen from a lawn management or tree feeding program in its proximity.
Fertilizer applications should be timed a few weeks before a new planting, just after green shoots have emerged in spring, and after flowering is complete in fall. This will provide the nutrients for healthy, plentiful blooms.
It Was Cut Back Too Early Last Year
When your iris flowers have faded, and you’re left with nothing but foliage, you might be tempted to cut its leaves down to tidy things up and give other perennials the spotlight. But that would be a mistake.
Iris leaves should be left alone until the very end of the season when they’ve endured a major frost and have begun to brown. This is a sign that they’ve stopped photosynthesizing and are about to enter dormancy.
After blooming, plants direct all incoming nutrients toward their roots and future blooms. Leaving foliage in place will lead to larger, more abundant, and more beautiful flowers next season.
Its Flowers Were Eaten
Many critters are attracted to an iris plant’s sweet-smelling buds and colorful flowers. If you’re seeing stems with no heads, stems that are broken in random locations, or stems that have been chewed down to the crown, something is probably eating your iris.
While a rabbit is most likely to blame, irises are attractive to deer, squirrels, voles, moles, and birds. Critter damage can be particularly frustrating to a gardener since there’s not much that can be done to prevent it, and most of us want to be kind to the fauna and the flora.
While prevention tactics are hit-or-miss, flower damage from mammals is most often addressed with fencing or some deterrent:
- Try a sensor light if a chicken wire fence or raised bed doesn’t work.
- Some predator urines are available at stores and may be applied around the garden to reduce invaders.
- If a store-bought repellant doesn’t stop critters from feasting, add motion-activated sprinklers to shoo them away.
- You can also try sprinkling its crown with cayenne pepper, although this method is a very short-lived treatment.
Hopefully, you’ll find something that works well before next season, and your flowers will be back in full bloom.
A season without iris flowers can be extremely disappointing, but if its leaves are still green and look otherwise healthy, there’s a good chance the situation is temporary. Observe and investigate thoroughly to determine the probable cause and take action.
Be patient with newly planted irises and ensure rhizome tops are slightly exposed. Care for them properly and watch out for disease and pests. Through the process of elimination, you should be able to zero in on the cause of your flower failure and address them promptly. The next year’s blooms will certainly be fabulous!