Update: Iris douglasiana at Atlanta Botanical Garden

by Kathleen Sayce

Iris douglasiana seedling at Atlanta Botanical Garden

In January 2022, Raleigh Wasser, Horticulture Manager, Atlanta Botanical Garden, sent me a update about their lone Iris douglasiana plant, which is growing in an alpine style bed with excellent drainage. After reading Wasser’s article about the botanical garden’s alpine-style bed in the Rock Garden Quarterly, I wrote a blog post about it in June 2021. 

World of Irises readers may recall that this plant flowered last spring. The plant went on to produce a pod with about ten seeds last summer. Botanic garden staff collected the seeds and sowed them. 

Raleigh’s update takes up the narrative: “We germinated a douglasiana seed! Just put it in some potting mix and left it in a corner of our greenhouse. Of about 10 seeds this is the only one that germinated.”

I suggested she put that pot outside as winter ends, and perhaps other seeds might germinate. Seeds of Pacific Coast native irises may take one to three years to decide to sprout, even from the same pod. However, getting even one seed to germinate and thrive is wonderful! 

Reminder: Seeds of Pacific Coast native irises do not like to germinate in warm, humid conditions. These seeds are fine outside in the snow and rain, so long as it is not too cold. Zone 7, -10°F is about their lower limit. I suspect the Atlantic Botanic Garden greenhouse where the seedling germinated is cool, not warm. 

This extraordinary Pacific Coast iris and its offspring continue to deliver surprises in its Atlanta, Georgia home.

Iris douglasiana in Atlanta, Georgia? Oh My!

Kathleen Sayce, April 6, 2021 

   In the current issue of the Rock Garden Quarterly, North American Rock Garden Society (www.nargs.org), Raleigh Wasser, horticulture manager, writes about a rock garden at Atlanta Botanical Garden (atlantabg.org). Heat, summer rain, and humidity are inevitable in this location, thus this rock garden is a test area, not for alpine plants from around the world, but for tough plants that demonstrate rock garden style, in Raleigh’s words “creating alpine vistas at sea level.” 

Raleigh likes irises, (sensible woman), and writes about irids that do well at ABG, including several Sisyrinchium species, Alophia drummondii, Herbertia lahue ssp. lahue, Iris pumila, and Iris douglasiana. I read that paragraph several times, then wrote the editor of RGQ to ask Raleigh for details about the last species.

I. douglasiana flower, photo from 
Raleigh Wasser, ABG

The Iris douglasiana selection came from Garden in the Woods (www.nativeplanttrust.org ) in 1993, and was a tiny grassy tuft of leaves when Raleigh started at ABG. In the past few years it has grown and bloomed. I asked if it has set seed, and have not heard back. Raleigh sent me a few photos, and yes, the flower details in the photo show this is clearly an Iris douglasiana type PCI. 

This was confirmed with several SPCNI members who grow, hybridize and judge PCI, Bob Sussman, Garry Knipe, and Debby Cole. 

The miracle is that it grows in Atlanta at all. 

Boulders in the rock garden are from midtown Atlanta, 1989, from a building excavation. The soil is sand mixed with local red clay and topped with pea gravel. 

Iris douglasiana label and foliage
at Atlanta Botanical Garden. Photo 
from Raleigh Wasser, ABG

Slopes are 15 to 30 degrees. This long arc of rock and well drained soil faces south-southeast. Atlanta is zone 8a, with 52 inches of rain per year, hot humid summers and cold winters. 

So, by chance, this rock garden has neutral to acidic soil, the soil is well drained, and has a very tough I. douglasiana species-type selection that can weather the humidity and year round precipitation. I would not have bet money this could happen, but it has. 

Irisarians, from beyond the regions where PCI naturally grow, take heart from this success:  Excellent drainage in neutral to acidic soil, summer rainfall, and a tough PCI all came together to thrive in a Georgia rock garden. This environment provided just enough of the right conditions. 

For more on growing PCI, check the SPCNI website’s gardening information at http://www.pacificcoastiris.org/gardeniris_introduction.html, which offers tips for climates outside the West Coast. 

Thank you to Raleigh for writing about ABG and including comments on irises.