If you use card board do not use colored card board, only plain brown stuff.
Many of the colored card boards will be there for a long time and some are treated with fire retardant material which I have found out when burning it. Some need a hot, hot fire to ignite.
A woman on another site a few years back had made a raised bed with card board on the bottom to kill grass.
She said she watered but the water most ran out the bottom flooding her lawn.
When she pulled the soil out to check the cardboard, the colored stuff was still solid as could be which was the reason her water did not soak into the ground. It could not penetrate the card board.
This was not a new bed either, it was a year old.
