Iris--TOW
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