I tried my first arilate irises over fifty years ago; they were the
regeliocyclus hybrid 'Chione' and Iris susiana. Both bloomed, but neither
lasted more that a year or two more. I still have old Kodachrome
transparencies of both (or maybe later acquisitions of both). Subsequent
trials of Iris susiana in pure grit filched from the local railroad tracks
(I was still in the thralls of the "good drainage" mentality) resulted in
plants which, although they persisted longer, gradually starved to death.

Years later I tried again with a nice assortment When these were received,
I noticed something about them which at first puzzled me: it was obvious
that they had been grown in clay, red clay.

When inexpensive and readily available stocks of 'Dardanus' became
available in the recent past, I decided to give these plant another try.
Several other hybrids and species were obtained at the same time. They were
planted in a raised bed of the local red clay. Most grew vigorously and
bloomed. Still under the influence of the drainage myth, I assumed that the
raised bed (it was raised well over a foot high). Most of the plants,
especially the bigger ones which had bloomed, were already rotting when I
dug a few in June to check them.

It was at about this time that I had some exchanges with John Lonsdale
about the culture of these plants. What I took away from that was the use
of polycarbonate sheets to cover the plants after they bloom.

I joined the Arilate Iris Society in 2013, thanks in part to Dennis'
preiodic reminders to this list about that group. I obtained fifteen
hybrids and planted these out in a simple, ground level (i.e. not raised)
cold frame out in a field (my community garden plots) in late summer. All
grew and the following year some bloomed. Sometime in May I covered the
frame with a glass door (I'm getting too old for this and have since
acquired some polycarbonate sheets). All of these (and some other arilates
acquired elsewhere) sailed through the summer without a hitch. Many
retained their foliage, some became completely dormant.

In this part of the country, arilate irises ripen during May; guess which
month of the year is typically our wettest month? They will never dry out
if you don't cover them.

I got a nasty surprise in September when I removed the glass: no sooner
was the clean, vigorous looking foliage exposed to rain than it began to
get spotty and die back.

But the plants are obviously vigorous and otherwise healthy, and I'm
already counting next spring's chickens.

The frame, which might strike some of you as useless, does have a
function; it prevents water running across the surface of the ground from
entering the framed area.

In the literature, especially the rock garden literature, there are
articles (some of which read like calculus puzzles and kept me tied in
knots) discussing drainage. To make a long story short, I think it's
largely bunk as far as most summer dormant plants are concerned. What the
plants in question need is not good drainage: as long as they are growing
actively , they will probably thrive in a pig sty (at least until the pigs
get them). But as the time for dormancy approaches, what they need, and
this seems to be non-negotionable, is dry soil. That soil can be dried up
muck, dried up stable bedding, the local clay dried from its formerly
waterlogged condition - the sort of soil doesn't seem to matter, as long as
it is dry.

When these plants are put into very sandy, gritty media they do get rapid
water passage; that rapid water passage also takes water soluble nutrients
with whatever else drains out. It amounts to a starvation regimen.

Put them in the richest goop you can get your hands on and watch them
thrive - just remember to start to dry them off as they are coming into
bloom so that by the time they are entering dormancy the medium around the
rhizomes is dry.