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.