9 Reasons to Plant Bicolor Irises This Season
Interested in growing some bicolor iris this year but not sure if it’s the right plant for you? Wondering what kind of iris you can grow in your southern garden? In this article, certified master gardener Liz Jaros offers 9 reasons why you might want to give this lesser-known, warm-climate iris a closer look.
Though not a member of the Iris genus, the bicolor iris (Dietes bicolor) hails from the same plant family (Iridaceae) as its German, Siberian, Dutch, and Japanese iris cousins and shares a lot of the same characteristics.
Its creamy white flowers are more orchid-like in form than the common iris, but they share the same pattern of 3 small upper petals and 3 large lower petals. They also have strong ‘signals’ near their throats, rhizomatous roots, and strappy, upright foliage.
The biggest difference between bicolor iris and plants from the better-known Iris genus is their region of origin. Dietes bicolor is native to South Africa and partial to warmer, more humid regions, while its European and Asian relatives prefer cooler, drier climates.
Often casually referred to as an African iris (due to its native roots) or a fortnight lily (because it blooms every two weeks and has lily-like leaves) and often confused with the bi-color iris (which is a term commonly used to describe a traditional iris with multi-colored petals), a true Dietes bicolor iris is its own unique genus.
Averaging 24 inches in height with a full, round habit and sending up multiple flowers per stalk, bicolor iris plants are hardy between zones 9 and 11.
They tolerate soil that does not drain perfectly and will thrive in multiple sun conditions. We think this is an underrated perennial worth checking out, and we’ve come up with 9 reasons why you might want to plant some in your yard this season.
You Love a Natural Garden Aesthetic
When planted en masse, bicolor iris creates a natural, grassland vibe in the landscape. Its leaves sway and move in the breeze, its creamy flowers float above the foliage, and it blooms off and on from spring to late summer.
After flowering ends, bicolor’s dense root system discourages invasive species from moving in, while its concentrated foliage holds a nice green color long into the fall.
Do not plant this genus in rows or try to control its spread if you want a natural effect. Let these plants wind and curve at the edge of the property, or give them some room to roam near a creek bed. Work some smaller, native perennials into the mix and let them mingle as they would in the wild.
You Live in a Warm, Humid Part of the World
To grow Dietes bicolor as a perennial, you’ll need to live somewhere warm and moist. As natives of South Africa, these durable beauties have a hot history and will not survive in areas that receive temperatures below 25 degrees Fahrenheit.
Botanists have given this perennial a hardiness zone range of 9 to 11, which means northern gardeners are out of luck unless they want to dig them up and bring them inside for winter.
Dietes also enjoy more humidity than their European iris cousins and wilt in the hot, dry sun. If you’d like to grow them in an arid climate, plant them where they will get some relief from hot afternoon rays and be prepared to provide supplemental watering. A hose or irrigation system with a mist setting will typically do the trick.
You Have a Large, Sunny Area With Moist Soil
Bicolor irises will bloom best in areas with at least 6 hours of sun per day and prefer moist soil. They can even handle long periods of standing water during their active growing periods. This makes them particularly well-suited to low areas or waterside locations where moisture levels may rise and fall throughout the day, week, or year.
During periods of drought or in locations with soil that tends toward dry, provide supplemental watering as needed to keep your bicolor iris roots moist, healthy, and active. This may mean 3 to 5 times per week, depending on your unique conditions, humidity levels, and rainfall totals. Or it may mean once or twice. If your irises are wilting or sagging, they are probably thirsty.
You’re Looking for a Neutral Addition to Your Perennial Pallete
Bicolor irises pair well with almost everything you may already have in the yard. Their neutral white flower color does not compete with other perennials or call out for attention. Although stunning in a large mass, the genus is also completely comfortable in a supporting role.
Plant Dietes with other whites and creams for a serene moon garden effect, or work them into a bold tropical landscape to provide contrast. They can also be incorporated into a soft pastel palette with pinks, purples, and yellows.
You Need Texture in the Landscape
Bicolor irises are basically evergreen plants and will hold their leaves all season. For this reason, they serve an aesthetic purpose in the landscape even when not in bloom.
Their sturdy, upright form and fountain shape create an excellent background for low-spreading perennials. Their foliage also provides a great, spiky contrast against finely textured or brightly colored leaves of other flowering plants.
You may notice some brown or wilted leaves later in the season, particularly on the undermost layers. These can be snipped off with a pruning tool or pulled by hand to keep plants healthy and green all year.
You Want a Unique “Thriller” for Your Container Garden
The same attributes that make the bicolor iris a beauty in natural settings make it a winner in the container garden. With a sturdy, upright leaf structure that holds its color all season and a neutral, creamy white flower palette, this plant works really well as a central figure in a patio pot or a raised bed.
Pair bicolor iris with annuals that will provide enduring color, and layer in some trailing plants to spill over the side. You’ll have a unique arrangement that stays beautiful from spring to fall, and you can leave the irises in place to come back next year.
Plan to divide every other fall to keep your container from getting crowded. And cut leaves down to keep growth vigorous and healthy.
You Want to Attract Pollinators
With colorful yellow splotching at their throats and a light, sweet scent, bicolor irises are attractive to pollinators like butterflies, bees, insects, and birds. When planted in large quantities in a sunny location, their leaves and flowers provide grazing options to a host of pollinators.
Plant them in the vicinity of food crops to help encourage a robust produce season, or work them into an urban patio design to provide pollinating opportunities where they can be scarce. Since bicolor irises are so easy to care for and thrive even when slightly neglected, they make a natural choice for pollinator-focused companion plantings.
You Can Give Them a Little Room to Run
Since bicolor irises spread via rhizome expansion and seed dispersal, they multiply easily and can consume a large area rather quickly if left unchecked. This can be a good thing if you’re looking to suppress weeds, crowd out invasive plant species, or replace traditional turf grass, but maybe not so good in a small urban backyard that is tight on space.
Remove spent flower heads before they go to seed and drift in the wind to control their spread. This will stop them from self-planting elsewhere on your property. You can also control their territory by digging them up and redistributing new rhizomes or installing a hard border that will prevent roots from running where you don’t want them.
You’d Like to Control Erosion
In landscapes with sloped terrain or prone to erosion, bicolor irises can be effectively used to hold soil in place. The plant’s dense, fibrous root structure can play a major role in preventing surface loss from wind, rain, and running water.
They also keep the earth aerated and loamy while discouraging soil compaction that can render the soil less fertile.
Since the genus can tolerate wet soil and periods of standing water, bicolor irises can be planted near the shore of a lake or pond that rises and falls with rain levels.
They also work well on a hill or switchback that descends to the water’s edge, creating visual interest and structural integrity. So planting bicolor irises for erosion control is both pretty and smart.
While Dietes bicolor is not a plant genus on the tip of everyone’s tongue, we feel it should be! With a bloom period that essentially comes and goes all season, a foliage shape that proves attractive in the garden even when the plant is not flowering, and a tolerance for soil that does not always drain perfectly, bicolor iris is definitely an underrated option for meeting some of your most basic garden needs.