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sheet mulching

You don’t need to be this specific.
All of the resources you need are free and abundant if you live in a city. There are coffee shops EVERYWHERE that are happy to give you bucket loads of coffee grounds (nitrogen). Cardboard (carbon) is also all over the place, especially behind grocery stores or in your neighbors recycling bins. Bags of leaves (mulch) are being placed on the curb free for the taking, so there is no reason not to utilize them in your garden.
Why do this? To build healthy soil from the top down, smother weeds, and establish new garden beds without any digging.