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Iris x robusta ‘Gerald Darby’

Categories:Irises Perennials

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Iris ‘Gerald Darby’ is my favorite iris and I’ve only seen it flower for one season. It is new in our garden and it is brilliant. I grow, plant, and photograph a lot of perennials, thousands. Gerald Darby reaches my heart in a way few plants manage.

Maybe it is because my wife Angela decided to plant irises this year and I’m predisposed to have an emotional connection to the plants she loves. Maybe it is the impossibly dark stems. Maybe it is the background of autumn fern and the foreground of California poppies. Maybe because it is a hybrid of two native irises. Or those perfect flowers. Maybe it is all these things and more.

Watching this iris grow throughout its first season reminds me of why we garden.

We bought it for the foliage, which is dark indigo when newly emerged. We certainly were not prepared for the beauty of those sinuous blue-black stems or that first flower. The foliage lightens over a period of six weeks or so.

We found Gerald Darby at a local nursery as a leftover from the previous year. It had no tag and I reckon it was passed over for big-flowered German iris. There it sat, waiting, until we happened across those dark blue leaves.

Gerald Darby has the scientific name Iris x robusta, indicating it is a hybrid of two native irises.

Gerald Darby is a hybrid of Iris versicolor and Iris virginica. It is named after hybridizer Gerald Darby and named in his honor. It was introduced in 1967, but only now seems to be finding the attention it deserves.

After consulting the USDA Plants Database I’ve indicated Gerald Darby as a native plant. The database does not include this cultivar, but it does identify Iris x robusta ‘E.S. Anderson’ as native. ‘E.S. Anderson’ is also a hybrid of Iris versicolor and Iris virginica.

Gerald Darby likes wet, clay soils but will do fine in average garden soil.

Both of Gerald Darby’s parents grow best in acidic, persistently wet soils. Iris versicolor, blue flag, and Iris virginica, southern blue flag, are plants of bogs and shorelines. This is also true of yellow flag – Iris pseudacorus. While these species all naturally occur in wetter places, they have proven to be adaptable in average garden conditions.

Keep all of the iris species discussed here watered the first season. Sun is preferred in order to flower. I have iris planted in shady spots and they rarely flower. I like the foliage, so they are safe even without their blooms.

The leaves grow two to three feet high and emerge a dark blue that lightens over time. Leaves are an inch across and in my mind are a happy medium between the larger, coarser leaves of the bearded irises and the thinner wraith-like presence of Siberian irises.

You may see photographs and descriptions of Gerald Darby online that are not the deep vibrant purple of the flowers pictured herein. Gerald Darby also produces paler lavender-toned flowers, often on the same plant, as seen here. It is not a trick of the light…these images came from the same season on the same plant and are reproduced faithfully for color fidelity.

It is my belief that while the bearded irises are surely impressive, they are not the most beautiful of the species.  The graceful presence of our native irises is hard to surpass.

Stalks are three feet tall and are strong. The proportion of the flowers to the stalks is a beautiful thing. A hard rain bent the stems over a couple of weeks ago and my heart sank. Over a period of a few days, I was surprised to see the stems slowly right themselves and return on the journey towards the sky. Daucus carota, Queen Anne’s lace, flops and never gets up. You don’t have to stake flopped over Queen Anne’s lace by the way. The stems will bend themselves vertically and while you’ll have shorter plants, they will be sturdier.

It would be a shame to stake any iris and many do tend to flop under the weight of their flowers. Flowers on our plant are a dark, royal purple, the ideal of what an iris should be.

I would suggest planting the blue and purple flowered irises where there is shade in the early evening. Try to plant against a background that is consistent, maybe dark yews or as in our case hydrangeas and autumn fern.

The color blue recedes in the landscape

Many irises, and Gerald Darby is no exception, can look washed out in sunny spaces. Further, the color blue recedes into the landscape, whereas the hotter colors such as red and yellow advance. What this means is that blue flowers can get lost. It is an interesting phenomenon as I am always surprised how dark blue colored flowers can be hard to see unless we look for them. I certainly don’t have to look for butterfly weed in the landscape. It is a beacon.

The irises are superb vertical elements in the garden and one might argue the sword-like foliage is their greatest asset in garden design. Still, if you site iris carefully you can enjoy the best of all they have to offer.

Genus/speciesIris x robusta ‘Gerald Darby’
Of notehybrid of Iris versicolor and Iris virginica, both of which are native to North America.
Fall colorinsignificant
Water requirementsaverage, moist soil conditions, high
Soil qualitywell-drained, average
Suggested use(s)bog gardens, cottage gardens, mixed borders/perennial beds
Hardiness zone(s)4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Typeherbaceous perennial
Nativeyes
Invasiveno
Deer resistantno
Deciduous or evergreendeciduous
Flower colorpurple/violet
Bloom periodmid to late spring
Exposurefull sun, afternoon shade

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