I put cardboard down and covered it with mulch inside my tire garden. Today I decided to plant three gardenia cuttings I rooted. Well, digging a hole through the cardboard was about as much fun as I expected it to be. But it can be done. I think it might be easier because the cardboard was still moist from our last rain.
A friend said she was using the idea of cardboard or newspaper under mulch for weed suppression. I hope she watered it. I put mine down where I wasn't trying to grow anything, I just didn't want to use the lawnmower and a hoe. I didn't put the cardboard close to plants. What I planted today, however, will require watering occasionally.