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Why do rhizomes need sun?

Posted by veryzer 5a IL (My Page) on
Tue, Jul 31, 12 at 20:14

It just seems strange given that a fan has many, many times the surface area. Just curious.


Follow-Up Postings:

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RE: Why do rhizomes need sun?

They don't need sun. As a matter of fact, I just learned that many growers plant the rhizome entirely under the soil, especially in very hot areas, so that the plant does not get burned.

The reason people tell you to plant your iris with the top of the rhizome exposed is because irises need good drainage or they can get bacterial rot. Rick Tasco at Superstition Iris Gardens says they plant their rhizomes just beneath the soil. He notes that rot is from injuries breaking the skin of the rhizome through which bacteria can enter. If there are moist conditions the bacteria are more numerous and can move about more easily to infect the plant.

Tasco recommends experimenting in your climate/soil conditions to find out what works best for you. I'm going to start planting 1/2 beneath the soil and 1/2 with the top of the rhizome exposed to see what develops here in So Cal.

If you let a lot of leaf litter and decomposing mulch sit on top of the iris you may be creating fertile conditions for bacterial rot as well, that that's something to be aware of.

Renee


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RE: Why do rhizomes need sun?

It was Chuck Chapman who gave that info. Here's a link to the discussion on Iris Lovers on Facebook.

Here is a link that might be useful: Iris Lovers Suzy Schneider post


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RE: Why do rhizomes need sun?

Thanks for the link. I've switched from planting mine half out/half in the soil, to planting one inch deep, and I always leave the roots on. It's convenient that there isn't such a big problem with nematodes here, so that the fact that we need the roots to keep the rhizomes from blowing away in the winter isn't a problem. We can have wet years, and dry years, and some parts of the city have clay soil, and some sandy, so a middle of the road course is best here. The soil changes from one side of my property to the other. It's sandier towards the creek, and gets more clay in it as you go upland. The rhizomes tend to migrate up to a half in/half out position for most of the iris. I've never done the bleach soak that all the folks on the Facebook group were adamant about, and haven't had any new iris rot, but I have had the dirt blow away out from under them, and they end up dried and shriveled and frozen. So, if it is an open winter, I need to mulch with branches or something to keep the soil in place. If it snows a lot, I need to get out as it is melting and clean all the debris away from them. Talk about frozen fingers. It is during those years that the bleach soak would be good insurance. Since I don't know which winter weather I'm going to get, I may take it up as a practice.

I have a lot of respect for the folks planting 10K rhizomes at a time.


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RE: Why do rhizomes need sun?

Thanks, that makes much more sense.


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RE: Why do rhizomes need sun?

I have never soaked mine in 10% bleach water before either, but I'll bet I would not have gotten leaf spot here if I had. I will from now on.
Barb, I can't imagine your winters!
Renee


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RE: Why do rhizomes need sun?

I don't know, Renee. To get a disease you need a pathogen, a host plant, and the right conditions for the pathogen to grow. I wondering if the weather was just stacked against you. Was it mostly new iris that got the spots, or is it just in certain places in your garden, or is it sort of all over the place? If it was generally all over, it might be good to note if there are iris that don't have it. Well, the culture would have to be the same, I guess. Maybe the more crowded iris might be more susceptible. But knowing if some iris are resistant would a good thing. Setbacks are disheartening. Can you try some fungicide next spring?


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RE: Why do rhizomes need sun?

It has been much cooler and moister here than usual for the past three summers. I used Daconil this year in early spring and again at the end of the bloom season.

I think I introduced it with some nursery irises last year. It only affected the irises in one area of the garden. This year I divided almost everything, and I have been extremely diligent about removing affected leaves and about pulling off every old leaf, even before they get brown. I am hopeful that I have eradicated it and will no longer have to spray.

I have been told that Beverly Sills and other light pink irises seem to be more susceptible to it. I cut off all of the foliage of Beverly, sprayed, and moved the rhizomes to the back 40, and they were spot free this year. Keeping my fingers crossed!
Renee


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RE: Why do rhizomes need sun?

Sounds like you have the bases covered. I hope the weather is more amenable next year, and that all your work pays off with clean, lovely iris!


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RE: Why do rhizomes need sun?

Have always wondered when it is appropriate to cut back the foliage on iris. My bed bloomed beautifully last year but hardly at all this year.


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RE: Why do rhizomes need sun?

I will answer, but really you should have started a new thread for this. You will get more responses that way.

Maybe your iris are getting crowded and it is time to dig them and throw out the old mother rhizomes and replant the new ones. When iris get crowded they don't bloom as much.

If you have reblooming iris, I don't think I would cut them back now. I don't have any that rebloom, but I still don't cut them back at all until it is going to have a heavy frost here, or sometimes I leave them all winter and then clean them up during a thaw in February. Some people cut them back at the end of summer or if they are looking nasty, which yours might be since it has been so hot this summer. I think it is up to you.


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RE: Why do rhizomes need sun?

Thanks, and yes I know better.


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