rebloomers more prone to rot?

jostus(7)May 23, 2009

With all the rain NYC has received this spring I have unfortunately lost much of the blooms on my re-blooming bearded iris's.I usually get some soft rot during times of heavy rain but this year has been the hardest on my plants.I had to lift out many of the rhizomes so that they may dry sufficiently.These were intermingled with non rebloomers none of which have soft rot nor ever have.Often the problem occurs a second time in the fall when heavy rains return just when most are either blooming or sending up stalks( my non-rebloomers are again unaffected)

I have decided this time when replanting to simply 'sit' the rhizomes of the re-bloomers on top of the soil so that only their roots penetrate into the soil thus allowing the rhizomes themselves to dry quickly after downfalls of rain.I decided to do this after seeing the way many of the rhizomes on my re-bloomers tend to grow straight up out of the soil (Fully exposed) after having been left undisturbed for several years( high humidity during summer?)These are never affected by rot and send down roots into the soil that are sometimes themselves partly exposed to air.

My questions are the following...Has anyone else noticed an increased vulnerability to soft rot amongst re-bloomers when compared to non-re-bloomers or is this just my bad luck? Has anyone else simply sat the rhizomes on top of the soil?what has been your experience with that? and lastly Does anyone else's re-bloomers grow rhizomes straight up out of the soil in areas of high summer humidity?

Responses would be greatly appreciated


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eroctuse2(z5 SE Michigan)

Rebloomers have always seemed to have poor form and substance (IMO), so I avoid them. Therefore, I'm no expert, but I do have an idea of something that could be a factor: fast, lush growth is usually weaker than the slow and steady (seems true in many cases involving lifeforms), and in order to rebloom an iris has to go through two cycles within one year.

That could be meaningless ramblings from an undereducated irisarian, or there might be something to it.

I'd be interested to hear from the more experienced rebloom enthusiasts.

    Bookmark   May 23, 2009 at 11:04PM
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hosenemesis(SoCal Sunset 19 USDA 8b)

I have only ever had two irises rot, and both were rebloomers.

Again and Again never got off the ground, and I have lost three Frequent Flyer rhizomes out of five.

Anecdotal evidence, of course, it could be that they were in bad spots.

    Bookmark   May 24, 2009 at 1:03AM
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iris_gal(z9 CA)

I have heard of using 2 inches of sand on top of the bed so the rhizomes sit on that ~~ was not explained how to accomplish but did come from an authority. Shall look for the article.

    Bookmark   May 24, 2009 at 2:15AM
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From my experience the growth on re-bloomers is not any faster that that of non-re-bloomers only that instead of going dormant during summer they continue slowly growing( being unaffected by the higher temperatures of the season) Also I don't understand why their 'form or substance as a whole(group) would be any less then that of non-re-bloomers if the plants are well grown and don't encounter problems. and to be honest even with the rotting of the rhizomes I spoke of,many surprisingly still had flowers of high quality, I on the other hand decided it would be best to cut them off along with half the leaves some of which had begun to yellow in order to save what was left of the poor rhizomes from over exhausting themselves and possibly losing them completely. By the way the rhizomes have dried quite nicely and I now see small root "bumps" forming on their undersides(I guess they are as determined as I am Lol). Some roots have even poked into the soil below. I am very happy, It would have been devastating to have lost so many.Maybe its just wishful thinking but I feel very optimistic that with simply sitting them on top of the soil I have perhaps ended my problems with soft rot on my re-bloomers in a humid climate. I am however very interested and willing to experiment with the 2 inches of sand on the bed to sit the rhizomes on top of. Please iris_gal do post your article as it may be very useful to me as well as others.
Thank you all for your responses

    Bookmark   May 24, 2009 at 7:43PM
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iris_gal(z9 CA)

Here's the entire article. Hope I'm not violating copyrights.
I too have been disappointed in form on many rebloomers.

Sand and Soap
by Marie Gebert, Connecticut, from January 1998 Bulletin.

As a "backyard entrepreneur" I've had my share of horticultural woes; also access to other people with similar problems. Our most common complaints in growing bearded irises are bacterial soft rot and our buddy, the iris borer. Here's what I have done to combat these woes.

A lot of our bearded irises reside in an organic vegetable garden. I heard about a safe preventative for borers that sounded worth a try, and have been using it for five years now with great success, as have other people in our northeastern Connecticut area. Use a mixture of one half cup of Murphy's Oil Soap to one gallon of water. Spray on the iris leaves weekly (or after a rain) from early May to late July. This should be used after any other sprays, (for leaf spot prevention, etc.), so the other sprays take effect before sealing the leaves with soap. I'm not sure if the soap confuses the moth by changing the odor of the leaf, or simply suffocates the egg, but it's cheap and it seems to work. Most of all, it is safe -- for kids, pets, and wild birds.

As for "spring mush", as I call bacterial soft rot, I've tried most everything -- eliminating fall fertilization, mulching with straw, pine boughs, wood chips, soil, not mulching at all, you name it. Also, I removed the mulch right on time, too early or too late, all with the same resulting soft rot. The beds are raised to prevent the irises from having "wet feet", so I was practically resigned to the considerable problem here in our cool, damp climate.

In 1995 we put in a new bed with a raised base of new top soil and a little fertilizer. Instead of coming to the top of the rhizome with soil as we had done before, we topped it all off with washed sand. The light bulb went on! Bacteria need a "friendly environment" to increase. Washed sand is basically sterile, so I intended to use it to keep young weeds down. We applied an inch or more to all the raised beds ands even mounded it up around the base of each plant; something I would never successfully get away with had it been soil. By spring the sand settles to rhizome level, but offers a thicker "mulch" for winter. I then went to the older beds, removing the soil from the rhizomes and filling in with sand. In the spring of 1996 there was no evidence of rot. Granted, it was a very good year for irises in our area, but even in the best of years I have never had such success. This past summer we had similar results. A few more years with equal success would convince me we had a solution to our rot problem. Meanwhile, others with similar soft rot problems could test this method. It would be interesting to know if this works for people in other regions.

Editor's Note: If others have tried the "sand method" for control of soft rot, we would like to hear how it worked for you. We could report results in a later Bulletin for the benefit of other iris growers.

    Bookmark   May 24, 2009 at 8:12PM
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