Growing species Iris in planters when your garden and climate don't work

Kathleen Sayce, June 14, 2020

In 2017 I moved two irises, Iris attica and I. hartwegii australis, from the open garden to planters where I could control rainfall and drainage. I wrote about this in Fall 2017 for World of Irises. 

Iris hartwegii australis, photo by Richard Richards

Iris attica in flower

I used styrofoam planters and a planting mix with ample pumice, to ensure good drainage. Both planters went alongside the east side of my house under the roofline, to reduce winter rainfall. On average, this lowers the winter rainfall by half, from 86 inches (cm) to 43 inches (cm) per year. Both planters are otherwise open to rain, snow, hail, and in sun half the day.

Iris hartwegii australis after planting, early spring 2017

After planting, the surfaces  were covered with granite chicken grit (5 mm) to provide surface stability in heavy rain. The planters were placed in a group near a hose bib so that summer watering is easy to accomplish. We have bird baths nearby that we clean and refill every day in summer; watering the planters is easy. At least once a week I soak both planters, mimicking summer rainfall. 

Iris hartwegii australis, spring 2020

Iris hartwegii australis has not yet flowered, but it has put out several new fans, 6 fans when planted, 27 fans today. Compare the original planting to the planter this spring, from early spring 2017 to late spring 2020 in the accompanying images. 

Fans are larger, healthier, their color is excellent, and there are more fans each year. Meanwhile, the remaining plants in the open garden have vanished.

Four growing seasons later, it is clear that Iris attica thrived with the move, though seed set has been low. Despite its small size, this species fills its planter every two to three years, after which I take it out, prune it back and replant. Two years ago, I sent more than twenty rhizome pieces to a regional iris group for their summer sale. The plant left in the garden disappeared. 

Iris attica flowering in 2018, this is a happy plant!

For both species, I concluded that winter wet and summer drought in a fine sandy soil did not let them survive or thrive. Use of compost, mulch and fertilizer was not enough for either species. 

Conditions in the open garden were simply not close enough to their native habitats. 

 By keeping both species in planters, using a potting mix with compost and pumice, placing these planters under the eaves and near a hose bib, and with occasional foliar sprays, both have done better.  

I am still working on promoting flowering for I. hartwegii australis. I would like to know about your fertilizer regimes in your gardens for winter dry, summer rainfall species, to help me decide how much more I should be doing. 

Every spring I think, this might be the year when IHA finally flowers! Meanwhile, flowers or not, I have been very pleased that this touchy Pacifica iris is still living in (or next too) my garden.