westy1941(Boulder County, CO)September 30, 2009

I know the rhizomes need their tops exposed slightly when planted; however, they are now in a mixed bed of hosta and a few other plants which I would like to mulch shallowly (an inch) or put compost on. Is it okay to cover them with mulch for winter and then remove it in the spring or must they be free of anything all winter (except snow!)...

Thanks in advance,


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If you cover your iris with mulch for winter they will rot.

    Bookmark   September 30, 2009 at 5:14PM
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westy1941(Boulder County, CO)

So only snow should be on them then? I want to put down some home-made compost in my beds but I guess you're saying I should sweep it off the iris rhizomes or just keep it away from that area entirely? Is compost as bad as mulch for iris? I have the rhizomes in clusters so that they can sort of be 'off by themselves'. I don't ever want to go through another borer infestation like I did this summer!


    Bookmark   September 30, 2009 at 7:49PM
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carlos42180(Z5 Chicago)

Do not mulch OVER the rhizomes. I've had great success mulching AROUND the rhizomes, as I also have Iris in mixed beds. They also perform much better and grow bigger than my Iris that are not in mulch. I have not tried any other type of mulch other than red bark cedar, so I'm not sure how compost will affect it. Borers are just something you have to be prepared for. They're never going to go away and you will always have a few.


    Bookmark   September 30, 2009 at 8:57PM
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iris_gal(z9 CA)

Mulch and compost both are moisture retentive --- a no-no on top of rhizomes.

Protection against borers in only possible with, egads, chemicals. There are lots of old threads on borers - a search will find them. I'm so glad I don't have to do a search and squeeze.

    Bookmark   September 30, 2009 at 9:01PM
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westy1941(Boulder County, CO)

Thanks again to all of you. I am going to do a search on Iris borers right clue why I didn't think of that before. I know about Merit (must be a chemical) that you're supposed to apply in early spring or spring sometime. And I guess I'll be mulching/composting close to - but not ON TOP OF the Iris!


    Bookmark   September 30, 2009 at 9:42PM
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