Thanks Peter! The coldest we have experienced here is -32F (-35.5C ?). It used to always get at least -10F (-23C). However, things have been warming for several years now and the coldest it has gotten was two winters ago with -22F (-28C). Then one year it only got down to 14F. Some years it dips to -4 or -8 for just a few hours which is just long enough to do damage. We also no longer have the generous snow pack that we used to. I generally plant for the worst case scenario as it is too expensive to lose things every few years. We also have WIND. The cold, dry air combined with extreme winds really dries things out. In the summer we can get dry winds that will take away the moisture in the upper inches of soil in a matter of minutes after I just finished watering. With all of these stressors my iris, which until this year, were all very old, did not multiply as most seem to expect them to do. No clumps. So far I don't think I have had bacterial rot, though I just may not have known what it looked like. Thanks for all your sharing. I will save this post. Colleen -----Original Message----- From: pbs-bounces@lists.ibiblio.org [mailto:pbs-bounces@lists.ibiblio.org] On Behalf Of Peter Taggart Sent: Sunday, November 25, 2012 11:18 AM To: Pacific Bulb Society Subject: Re: [pbs] Iris 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 <silkie@frontiernet.net> 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. > >