Peter Taggart
Sun, 25 Nov 2012 11:17:36 PST
Hello Colleen,
If you do not lift the dahlias from the ground, the mulch should be a very
good idea for them, and for most lillies too.
However bearded Iris tend to get a bacterial rot (and greenfly which
transmit virus), if warm and /or humid. cold and airy is better for them.
Many bearded Iris species will in fact burrow their rhizomes under the
surface of the ground, especially most of the Oncocyclus and Regelia
species, as well as Iris reichenbachii, variagata, attica, pumila..... Most
historic Iris have a lot of Iris Pallida in them, which is less fussy, as
well as I variagata, aphylla and pumila.
If these are planted in humus rich soils they tend to rot, though I have
found I variagata in particular more resistant.
In my experience, many of the bearded Iris, and in particular the ones
which do not grow with their rhizomes on the surface, are very reluctant to
put down roots if the rhizomes are not buried, as you have observed. - I
normally mulch them with grit or gravel.
I would expect that in your less humid climate that many of these Iris
would indeed do better planted well below the surface, but a gravel mulch
rather than an organic one would be more appropriate.

The UK has a very variable climate. My normal minimum winter temperature
here is about minus 10 c, however I have had two recent winters with
several weeks of minus 15c or colder at night. Occasionally winters here
are almost frost free.
Peter (UK)

On Sun, Nov 25, 2012 at 6:35 PM, Colleen <> wrote:

> Thanks Sean,
> While your area and mine are about the same temperature zone, I think you
> are probably more humid.  I think what is going to happen is that I won't
> be
> able to remember just where all the iris are planted so some will get
> uncovered and some will remain covered and the results will be a highly
> uncontrolled experiment!  Hopefully it won't be disastrous.

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