if i lived closer, i'd come over and take that purple grass

(i just love anything that's purple)
pull the iris up and replant somewhere else for the time being.
then use a
weed-whacker to cut everything down to ground level - make sure to rake up everything and dispose of it...don't want any stray
seeds being re-tilled.
then put a tarp down, or a thick layer of newspapers...at least 6 sheets thick - more like 10 thick would probably be better. use a good mulch to hold the paper in place.
after about 6 months everything in the bed should be dead. pull the mulch/paper aside and then pull up all the roots that are left and then till the mulch/newspaper back into the base soil and then
plant whatever you'd like there.
the quicker thing to do (and much more hard work) is to dig up everything. if you do that, make sure you get the roots for everything and any bulbs that are there. then replant with whatever you want there.