I've often been surprosed how shallow fern root systems are. Give yours a
gentle tug and see if they move.
OTOH, your trash may be someone's treasure. Those ferns could be worth
anything from $300 to nothing each, depending on their type, size, etc. Put an
ad in the paper or on local bulletin boards, with a pic if possible, along the
lines of "Free ferns---you dig and fill," and you may be surprised by the
response. The previous owners of my house seem to have done nothing but water
the lawn, so I inherited a jungle which I am slowly editing--partly bu hand,
partly by the above method.