Overcoming Climate—An experiment with Iris attica and Iris hartwegii australis

Kathleen Sayce, May 2017

Gardening on the coast in the Pacific Northwest, I grow many hybrids and several species of iris in the Pacifica (Californicae) group of beardless iris. The vigor of tall bearded iris is daunting—miss a year to divide and transplant, and my garden is overrun. I had to use explosives to clear areas (Joke! It just felt like black powder was more effective than a spade). 

Iris attica flowers, after seven years, three in the ground, four in a planter.

In 2010, the North American Rock Garden Society’s western study weekend was in Medford, Oregon. Gardens on the tour included Baldassare Mineo’s rock garden, Siskiyou Rare Plant Nursery, and a dozen private rock gardens in the area. A tiny bearded iris, Iris attica, came home with me. I planted it in the sunny end of a flower bed; it flowered the next year, and then began a slow decline. Four years ago, I removed it from the garden and planted it in a styrofoam box. 

In this new container, deep and well drained, tucked under an east-facing eave, Iris attica flourished and flowered. Which was when I discovered that squirrels, chipmunks and/or voles were eating the flower buds as they began to emerge and show color. [These varmints also ate my rainlilies.] But the plant was now sturdy and healthy; despite no flowers, Iris attica thrived in its new home. 

A working method to grow Iris attica in the Pacific Northwest:  a planter, a dry outside location (under eaves), very porous planting mix, and protection from animals during flowering. 

Last year we rebuilt the cold frame and added a band of heavy 1/2 inch wire mesh about a foot high all around the edge. This spring, when I saw buds emerging on Iris attica, I put the box in the cold frame; the mesh band was already open for spring. The result you can see, sans nibbling, is a planter packed with flowers. When it is done flowering, the planter will go back outside again. 

So, you are wondering, what is the link to Pacifica iris? 

I also have Iris hartwegii australis in my garden. This was grown from wild-collected seed, collected many decades before it was a listed species, then grown in a garden, and seeds from that plant passed to me. It flowered once and has been declining ever since. It’s native to mountains in southern California, which means the long wet winters here are probably wetter than it likes. It might quite like a box under the eaves. 

Iris hartwegii australis, ready to go into its new planter. Note the extensive root system--many more roots than on hybrid PCI plants. 

Richard Richards told me this about its native habitat:  

        “I. h. a. grows in its native range in decomposed granite with superb drainage.  It gets maybe 15 inches of water, occasionally in the form of snow, from November to April.  In the summer it gets a thunder shower about once a month.  There are often two or three inches of plant litter, mostly pine needles, above the young shoots in the late winter, and it grows up through this litter.” 

This spring, I dug up a sprawling clump of Iris hartwegii australis and tucked it in a styrofoam planter with a highly porous mix of coarse pumice and potting soil. I added some fresh compost and biochar for more soil carbon. I dressed the top of the planting mixture with granite gravel (chicken scratch), as its home mountains are geologically old granites of the Transverse Ranges in southern California.  Tucked along the eaves, the rainfall should be cut to under 40 inches, more like its home. This planter is close to a hose bib, and gets half days of sun (when we have sunshine). Summer soaking to mimic thunderstorms in the mountains is easy. 

Granite chips added on top, to help keep the soil mix in the planter in heavy rain, and in this case, to remind I. hartwegii australis of its natal home in the Transverse Ranges, southern California. 

My hypothesis is that native plants in these boxes do better than in thin-walled, dark-colored plastic pots, because the planting mix is deep and cool. I also grow Erythronium, Lilium and other bulbs in these boxes, where they can live for several years without transplanting. PCI seedlings do very well, though their roots will push through the styrofoam if left in there too long. In the winter, the well-insulated walls also protect the roots from freezing—just as in the ground. 

I’ll report back in a year or two on how this iris likes the planter. Or sooner, if it goes toes up!

Perils of Procrastination among Pacifica Iris

Kathleen Sayce
March 29, 2016

For those perfect gardeners among us, no pot of Iris seedlings ever goes a year or two too long before being separated and planted out. 

I'd like to know who they are, because this year I learned what happens when a styrofoam box of Pacifica Iris seedlings grows a year too long before division:  They grow their new roots into the box walls, out the bottom and into whatever medium is beneath. If the potting mix is to their liking, they also completely fill the mix with roots. 

A year past optimal planting out size, this dense mass of Pacifica Iris seedlings was not about to move to a new home easily. 

Thus, there I was on a sunny early spring day between storms, prying plants formerly seen as fragile out of what was formerly a porous and well drained potting mix of coarse perlite and half potting soil.  

First I tugged, then I tried to dig out some of the medium and gain some working space.  A few frustrating minutes followed with very little movement towards releasing these irises from their starter home. 

Sign of a thriving patch of Iris seedlings:  roots through the box into the gravel beneath. 

Then I resorted to my new favorite tool, a Japanese hori nori (gardening knife) and used the serrated edge to cut between plants, knowing I would cut through some.  Then I got tough, and held the box down with one foot and pried with both hands. Finally, most of the soil and roots emerged in a solid mass, which I was able to cut, not pry, apart. 

On the second box, I simply cut it open along the corners and took the mass of roots and plants out, and then cut them apart. 

Remains of the planting box to the left, a portion of the root mass to the right

Then I checked the plants from last year, which will go out soon, and sure enough, these young Pacifica Iris have also grown through the box into the ground and into the walls. Only a third the size of the older seedlings, they should come out a little more easily. . . 

Last year's seedlings are also ready to go, but I might not need to stand on my head to get these out, if I move them soon. 

There are undoubtedly some choice seedlings buried in the masses I planted––which is probably the worst of the unintended consequences. 

Why use styrofoam boxes for seeds? In the first few years of growing irises from seed, I found that dark plastic pots heat up in the summer, and when combined with normal summer drought, many seedlings died. I grow larger seedlings faster in styrofoam, which I deduce keeps the roots cooler. I may need to rethink the larger-faster-healthier choice and go back to slower, smaller and a little less vigorous. Or get out in the garden and repot them more promptly!