Since some construction at the house the stand of Siberian irises has rapidly claimed a large flower garden (and continues to spread). The growth is very dense and roots/rhizomes incredibly difficult. A few years ago dug out 4x10 area, planted new stuff but without enough attention the irises laid claim again within the year.

Don't want to put any chemicals down. My thought is to cut the plants down very low, then put layers of wet cardboard down? Thoughts on this vs black plastic? Has anyone used boiling water method? Would I want to wait a full year to put down a cover crop (say winter rye next fall)? What about sheet mulching? Would this be effective enough to eventually kill down the rhizomes?

This stuff is super sturdy and prolific! Thankful to the pretty flowers the irises have offered but hoping we can reclaim the flower garden with things that are not so prone to taking over. Expecting this may be a long process but, maybe not ?

Thanks so much!