Piece of 10'x10' 20mil thick HDPE liner.
HDPE or #2 plastic is less flexable than other liners like EPDM, PVC, Butyl, LLDPE, but is more puncture resistant and resistant to hydrocarbons and chemicals. Most Importantly HDPE the safest of the listed plastics for human and animal health.
Folding the plastic before placing in grow bed
Plastic in grow bed
Sides and ends folded up and stapled in place
1.5" Stand pipe, 1.5" ID bulkhead, 1.5" barbed fitting