7 Tips For Getting Your Irises to Rebloom
Scratching your head over a patch of irises that never bloomed? Or thrilled with your iris flowers this season and determined to enjoy a similar bounty next year? Certified master gardener and landscape designer Liz Jaros shares 7 tips for getting your irises to bloom fully and faithfully for many seasons to come.
Disappointed by modest, lackluster blooms? Fortunately, an iris can rebloom with the ruffly, full-color thrill you expected. Even if you had a ‘leaves only’ season where there were no flowers at all, rest assured that irises take a few years to establish, and many do not perform well initially.
Even if this was your second or third year, and a clump of irises that once bloomed beautifully is no longer sending up flowers, you may have to make a few tweaks to make them productive again.
While generally considered easy to grow, the genus does have quirks and preferences that demand your attention. Here are 7 tips for getting your irises to bloom again next year.
Give Them Plenty of Sunshine
Irises need at least 6 hours of sun per day if they are to flower to their fullest potential, and you should evaluate their location every year to ensure this demand is met. Has a tree or shrub grown over them to shade out some of their daily rays? Has something changed in the landscape to reduce the hours they spend exposed to direct light?
If your irises aren’t flowering, exposure is one of the first suspects to cross off your list. Even if you’re pretty sure they’re getting enough sun, take a day to record their exposure level at each hour as the sun makes its way across the sky. This will help you know if they’re getting the required 6 hours, which do not have to be sequential but must add up to 6.
If you discover they are no longer (or never were) planted in full sun, find a new spot in the yard that can meet their needs. Transplant them in fall or early spring, and you can expect a more impressive floral display next season.
Make Sure They’re Not Planted Too Deep
Improper planting depth is the mistake new gardeners and inexperienced iris growers are most likely to make, so I can’t emphasize this enough; Bulb irises should be installed four inches deep with the pointy end up and covered with dirt, but rhizome irises that are planted too deep will not flower. They must sit just below the soil surface with a little bit of rhizome exposed above the ground.
We are so used to digging a hole, dropping in a plant, and covering it with dirt (a process that works just fine for many of our less persnickety green friends) that it’s easy to think this rule can be broken. But when it comes to irises, if you don’t follow the recommended planting depth exactly, you will be disappointed by their show of blooms.
To make sure you plant your iris at the right time and depth so it will flower again (and again), follow these directions:
- Dig a trench (or a hole if you’re just planting a single iris) and mound some dirt up in the center.
- Carefully set your iris rhizomes on top of the mound.
- Make sure leaf fans are pointed up and hairy roots are pointed down.
- Let the root hairs cascade down over the mounded center so they extend toward the bottom of the hole.
- Backfill with dirt until just the tops of the rhizomes remain exposed.
- Water lightly and regularly until established.
Nothing shuts down a potential iris flower show quite like rotting rhizomes. As a plant with tuberous roots, irises are particularly susceptible to disease and decay resulting from poor drainage or overzealous irrigation. Water your irises evenly and regularly during their first season (or after transplanting) but never let them soak or sit in standing water.
Once established, your irises should only need water during periods of drought and extreme heat. So be careful not to give them too much water. If you suspect your irises are not flowering because they are waterlogged, dig them up and have a look. If they are squishy, slimy, or black, they are probably suffering from a moisture-related disease.
Unfortunately, a rotted rhizome will never flower again and must be discarded. Get some more irises and give it another shot. Now you know.
Divide Every Three or Four Years
This routine perennial maintenance task is not optional when it comes to irises. If you want your iris to rebloom reliably, ensure they don’t get crowded.
Although it takes them some time to establish, mature irises will multiply rapidly after a couple of years, and their rhizomes may take on a matted or buckling appearance. When this happens, leaf and stem growth will be suppressed, negatively impacting the generation of new flower buds.
To avoid overcrowded irises (and the inevitable reduction in blooms that results from it), you should plan to divide them every three or four years. This will restore their bloom potential, and you’ll have more irises to plant in other parts of the yard! Division should be done in the fall for best results.
Here’s how it’s done:
- Dig up the entire iris clump taking care not to damage roots.
- Lay the plant sideways on a tarp or hard surface.
- Using a flat-edged shovel or a sharp knife, slice the root clump cleanly in half.
- Repeat until you have several small clumps, making sure each section contains some leaves and some roots.
- Replant each section as you would a new iris, with leaf fans pointing up and root hairs draping down.
Try a Reblooming Variety
While most iris cultivars will only bloom once a year for about two weeks in late spring, some varieties will flower again later in the season. And others that will bud out two or three times more if they are properly cared for. If you can’t wait til next season for your irises to bloom again, why not plant a reblooming variety?
Reblooming irises perform differently in different hardiness zones, so keep your expectations tempered to your part of the world. Gardeners in cold regions will likely only get a spring and fall bloom, but southern gardeners with longer seasons might get several bud productions in the same year.
Many iris varieties fall under the reblooming classification, the majority of which are bearded varieties from the germanica species. Here are a few high-performing, reblooming cultivars you might want to try in your own landscape:
|botanical name Iris germanica ‘Best Bet’|
|sun requirements Full sun|
|height 2-3 feet|
|hardiness zones 3-9|
This lovely tall bearded variety is gently ruffled with pale lavender standards and violet blue falls. It has subtle white veining near the throat and thick yellow beards.
Reaching heights of up to 3 feet on sturdy stems, this cultivar offers two to three flower stalks per plant and will flower again at least once in late summer or fall.
|botanical name Iris germanica ‘Champagne’|
|sun requirements Full sun|
|height 2-3 feet|
|hardiness zones 3-9|
This elegant reblooming cultivar has a sweet orange blossom scent and a softly ruffled personality. Standards petals are peachy-white and firmly upstanding, while falls are golden apricot and down drooping.
‘Champagne’ has a golden beard the same color as its throat. You can expect this cultivar to bloom at least twice during the season.
|botanical name Iris germanica ‘Carmel Celeste’|
|sun requirements Full sun to part shade|
|height 8-15 inches|
|hardiness zones 3-8|
This reblooming dwarf bearded iris has scalloped, lemon-yellow petals and creamy white beards. Despite its diminutive stature, it packs a colorful punch, growing roughly 15 inches tall. It has a spicy citrus scent and typically flowers in spring, mid-summer, and fall.
Do Not Cut Them Back Until Fall
After flowering, most iris varieties will remain green and upright in the garden for the rest of the growing season. And it’s best to let them stay that way. Though you may be tempted to cut their leaves down once their flowers are gone, this will likely harm next year’s blooms.
After completing a flowering cycle, irises will use their leaves to harvest the sun and draw energy toward their roots.
Although it looks like they’re doing nothing but taking up space, your irises are actually working hard below the surface to create buds for next year. Leave them alone as long as you can, and cut them back to about 4 inches above the ground after the first frost. You’ll be rewarded with full bountiful blooms next year.
Pull Back the Mulch in Spring
Cover the rhizomes with 2-3 inches of hardwood mulch when all’s said and done for the year. Since roots are partially exposed, the genus is somewhat vulnerable to freeze-thaw damage, and mulch will help protect them from dramatic swings in temperature.
It will also help manage the flow of water and melting ice, discouraging it from puddling around a plant’s base.
With that said, it’s essential that you pull the mulch away from your irises in early spring. Uncovering the tops of their rhizomes will expose them to the sun’s rays and warming temperatures, encouraging healthy blooms for the season.
Growing irises can be frustrating, especially during the first few seasons, but once you get the basics down, they’ll be off and running.
Whether your flowers were spectacular this season and you want to make sure you get an encore performance next year, or you were disappointed by a poor showing and want to make sure it doesn’t happen again, with proper care and maintenance, you can up the odds your irises will bloom beautifully again for many years to come.