It's complete bunk as far as anything having to do with plants is
concerned, but seems to have some relevance growing plants in
wet-winter climates. (I have the Deno quote about "drainage" right
here on the laptop but am too lazy to include it.)
As far as I know, onco species like Iris iberica, paradoxa, barnumae,
etc., grow in climates almost identical to mine. I get a little more
rain in July and August than do, say, Erzurum and Van.
I suspect that the rain is delivered to the plants there as it is
here, by thunderstorms, and all at once. The soil here never stays
wet; it never rains all day, and it never rains in winter. (The only
all-day precipitation we get here is in the form of snow, like today.)
Nothing happens to the dormant irises here if they are rained on. The
plants don't need any kind of protection (except from rabbits) or
special cultivation techniques.
Growth in spring starts after the snow melts, with occasional rain and
hail precipitation "events". The hail sometimes destroys flower buds,
which is extremely annoying. (Understatement.)

Bob Nold
Denver, Colorado
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