Answer: There are no chemicals to eradicate the grassy weeds that won't also affect your irises. Pull the weeds while they're still young and then put several inches of organic mulch over the bed to suppress weeds that might try to sprout later in the season. Irises should be dug and divided every 4-5 years (when they're overcrowded they won't bloom well). When it's time to dig and divide the irises, plan on renovating the bed to exclude weeds in the future. The easiest way to do this is to place weed block fabric over the entire bed, cut holes in it for the irises, then plant them. Cover the weed block with decorative bark or compost. When it's time to renovate the bed again you can simply rake the bark or compost off the weed block and pull the fabric up, divide the irises, cover the bed with new weed block and replant the irises. This method will keep weeds to a minimum and allow your irises to thrive.
Best wishes with your garden!
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