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Grass in iris bed

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I need advice:

I have not been able to get outside much this Spring to weed and clean-up. As a result a field type grass (course and tall) has invaded my Iris beds. What is the most expeditious way to remove the invader without harming the Irises which are starting to form flower heads.


I plan to dig up the Irises this fall to thin them out and replant as they have moved up to the surface. They are generally mulched with hardwood chips. - J.G. -

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I am so sorry to be so long in replying, Jerry. We've been more dizzy this spring trying to keep up, than ever before -- must be our age catching up!


However, the timing is good in this way: Earlier, you didn't want to disturb the iris' bloom. However, now is the perfect time to dig and divide irises. Better than fall because now is when division does the most for iris borer control -- and the control of iris soft rot disease that goes hand in hand with borer management. Right now, the only place in the world where iris borers are to be found is IN the iris rhizome. They have finished feeding in the leaf but have not yet left the rhizome to pupate in the soil. So dividing irises now will knock the borer population 'way back, and thereby reduce the transmission of iris soft rot.


So in late June or early July we lift bearded irises, divide them, discard all soft and borer-infested parts. Then we clean the bed of any weeds, including fixing the edging if need be to prevent the grass running right back in. Then we re-set the irises.


(Digging is always our first choice when there is grass in any perennial bed, period. Grass is a top-dog competitor; no getting rid of it easily.)


There are some apply-over-the-top herbicides that have been developed to keep grasses in check when they get into groundcover juniper, etc. For the discussion of which herbicides are listed as safe for use in iris beds, see the post-emergent herbicide list in this bulletin from University of Georgia:



Keep in mind that the herbicide approach may be right for a production iris nursery but not such a great thing in the home garden. That is, 1) Those herbicides may kill the grass blade and a portion of the root, but can't kill a whole grass colony that exists part-in, part-out of the bed. And they cannnot block the grass re-entering along the same path it took the first time, such as a breach in the edging, or via mower-distributed seed. So the grass comes right back and you must repeat the herbicide application. Yet 2) in a private garden, iris beds are ornamental. With post-emergent herbicide use comes the unavoidable ugly period as grasses gradually die back. This must happen if the grass is to conduct a herbicide from blade to root. So the gardener has to look at ugliness. Then, adding injury to insult, the gardener must still remove the dead grass once it's all brown.


I hope this helps!

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