Jane McGary
Tue, 09 Mar 2004 09:31:35 PST
Regarding Iris species that grow well in my area, I would agree with Mary 
Sue that the Pacific Coast species and their natural and garden hybrids are 
the most dependable. They are useful for holding the soil on banks and for 
providing a grasslike foliage contrast when out of flower. The flowering 
period is short, in late spring to early summer.

All Pacific Coast irises flower best in sun here, although they can often 
be seen growing in woodland in the wild. They are adapted to persisting 
vegetatively when shaded, and to flowering and increasing by seed when the 
tree or shrub cover is removed by fire or other means. The seeds can remain 
dormant for many years, germinating when the soil is disturbed -- which 
suggests shallow sowing. This pattern is also observed in an iris endemic 
to my area, I. tenuis, the only western North American member of the 
crested iris group. It forms huge colonies in shade, but flowers much 
more  in open situations such as road cuts and under power lines.

If I can get healthy bulbs of Iris reticulata, Iris histroides, and their 
hybrids, they are long-lived in the garden in areas not watered in summer. 
They flower best if planted deeply. The problem is that most commercial 
stock is infected with ink spot disease, which soon debilitates the plants 
once they are not subject to the Dutch cycle of lifting, treatment, and 
controlled storage. Growing I. reticulata from wild-collected seed was a 
revelation for me: plants three times the size of commercial varieties, and 
setting big seed pods.

A few bearded irises have persisted here, notably I. albertii, wild forms 
of I. pallida, and I. subbiflora. I gave up on bearded iris hybrids years 
ago when I found that they do not tolerate competition from neighboring 
plants and suffer incessantly from diseases and slug predation. One might 
as well grow hybrid tea roses.

Some Juno irises seem to be doing all right outdoors here, in particular I. 
magnifica, I. vicaria, and I. bucharica, all of which are readily 
available. I grow them on the rock garden. Now I'm trying some selections 
of the Regelia species I. stolonifera outdoors. Oncocyclus irises cannot be 
grown in the open in the Pacific Northwest, and hardly can be grown under 
cover, unless you use fungicides and keep them dry until late winter.

The bulbous irises of the Xiphium section are represented in our gardens 
mostly by "Dutch" irises, which don't persist here over many years since 
their winter-growing foliage gets frozen. Far better is the "English" 
(actually Spanish) Iris latifolia, which comes in a number of color 
selections and doesn't make growth until spring. It should be a standard 
border plant in Mediterranean climate gardens.

Iris unguicularis is increasingly grown in the Pacific Northwest, though it 
can be expected to suffer in our colder winters. (I keep some in the bulb 
frame as insurance.) Its close relative I. lazica is more cold-hardy and 
flourishes here, as do most plants from the Pontic region, its home. It 
grows well in part shade but flowers better in sun, though its evergreen 
foliage can sunburn in the latter situation. It blooms in early spring and 
unlike I. unguicularis has little fragrance.

Spuria irises do very well here, but they are grown mainly by specialists, 
since they take up a lot of space for the sake of a very short season of 
proportionately small flowers. Siberian irises are fine as long as I get 
them in spots where the soil is retentive enough. Iris cristata cannot be 
grown here because of the slugs, which love it intensely. Japanese irises 
(I. ensata) do not flower for me, I suspect because of too much night 
cooling at this elevation; they are hot-and-humid-summer plants and do fine 
on the valley floor 1500 feet (500 m) below me.

Jane McGary
Northwestern Oregon, USA

More information about the pbs mailing list