[goodnesswins]

I have used cardboard to do what you are intending...just bury it well with good soil (thick newspaper works, too)

[metmom]

I’ve used cardboard as well, and putting a good layer of wood chips on it helps, too.

I have used landscape fabric in the past, but weeds can still grow through it. Cardboard seems to smother better and composts nicely after a year or so.