You can use old cardboard boxes as weed or grass killer!
I lay down cardboard under my raised garden beds to kill the grass in preparation for filling with dirt. The cardboard is plentiful and is biodegradable. It will just compost down under the garden.
Cardboard can also be laid down anywhere you need to kill grass or weeds, and then recycled when it’s finished the job.
This is a wonderful was to reuse a packaging product that may have just been tossed aside.