It will grow right through the mulch. Horrible stuff. I haven't yet tried any of the specific herbicides (like Sedgehammer), but have had some success with pulling it out over and over; eventually it slows way down or stops growing altogether. Good luck with however you try,

where's the agent orange when you need it? i'm going to try the mulched over cardboard & pulling. this stuff is a royal p.i.t.a.! i think i may have brought it in with some mulch. i read up on it on another site that says once there are tubers (nuts ) established that hebicides have little effect. one suggestion was to move to another house. i'm not after a perfect lawn. dandelions & dutch white clover are fine with me as i'm a beekeeper. but this sedge is taking over my flower beds & vegetable patch.

Understanding about sedges can help in controlling them some. Sedges evolved as wet land plants and althouigh theuy have adapted to growing in drier areas they still need that wetter than normal soil to get started. Mulches provide the ideal habitat for Yellow Nut Sedge to grow in, the cool, moist, soil they evolved in.
Correcting the soil conditions is one method of control and digging the "nuts' the rhizomes that produce the plants is another. There are poisons that you can spray that will kill the Yellow Nut Sedge as well as any other grass it contacts, but unless the soil conditions are corrected new seeds ,brought in by the birds, could germinate and grow to replace what you just killed.
I see Yellow Nut Sedge growing in lawns and gardens that are sprinkled every day but do not see it growing where the lawn or garden is watered only once a week or so.

Kimmsr....you are so fortunate. Nutgrass does not behave in the predictable way you've observed in other parts of the country.

There are plenty of post emergent herbicides that target grasses and sedges but will not harm broadleaf garden plants. We use a product called Sedgehammer in our perennial beds....sprayed right over the top of everything else.

I might add that our soil is very well drained and not irrigated, very rarely watered.

There are even herbicides that help control sedges in turfgrass.