>Is there some collective wisdom on when rot occurs? Doesn't seem to me
that you would get much rot in ground that was 40 - 45F even if it was
mulched. I was under the impression that it was warm (hot) and humid and
wet that promoted rot. Maybe springtime when you get the warming trend
that really warms the soil is when you need to be concerned about
clearing off the mulch to allow things to dry out.
The bacteria hard at work rotting down your mulch will give off quite a lot
of heat - have you noticed how warm your compost pile gets? So the ground
under a mulch will be warm and moist - very desirable conditions for most
plants, but for bearded irises I would reckon that would lead to rot - hence
my advice to Nancy. However, I do agree that extra vigilance in spring would
My experience of rot is this:
- worst time: spring, especially during that period of rapid growth. May be a
reflection of winter damage though - slug holes and weevil damage
(cockchafers are a problem here - they burrow into the rhizomes - a bit like
iris borer but not so bad (thank goodness!)) give a start point for rot.
Blackfly can act as a vector for rot. Do iris rhizomes split open in very
cold weather? We also get trouble after blooming in wet summers (although we
have not had a wet summer in several years) - cutting out and removing spent
stems may help, and getting rid of old leaves. Thoughts from others welcome.
- problem is always made worse by poor husbandry - lots of rotting leaves or
weeds around the base of the plant are bad news.
- fungicides help - Systhane (myclobutanil) I have mentioned before (use a
wetting agent) as a preventative. Where damage has begun, dig the plant up,
trim out the damaged rhizome, dry it off in a shed for a day and dust with
flowers of sulphur before replanting. Bleach is talked about in some US
texts, but is prohibited from commercial use in the UK (due to our lovely
COSHH regulations and other laws - sneeze and you have to fill out a risk
assessment - my girlfriend had to do a risk assessment for the office bicycle
last week, including how to avoid the possible risk of injury or death
resulting from falling off - answer - don't use it! She works for local
government - somehow you can tell!).
- some varieties are more prone than others - comes back to my comments about
hot colours not doing well in our climate. I'm sure Clarence will concur that
pink/orange irises are much more prone to rot than blue/purple or plicata in
- rot is always worst after long periods of damp weather - we had a very wet
spring a few years ago, and had real trouble with one or two varieties,
especially those planted where the ground was less freely drained - in fact,
I am convinced that wet is more important than temperature as a catalyst to
rot. Raised beds are vital.
More thoughts welcome!
Croftway Nursery, UK
Maybe we could not only edit our subject lines, but perhaps also add a little