Abstract: A cover unit 12 adapted to interlock with other such units having a top surface 14 capable of supporting persons. The unit 12 is formed of semi-opaque plastics material thereby providing for a required reduced amount of light to reach any plants located beneath the unit 12. A grid is provided by a plurality of recesses 18, 20 on the surface 14, the recesses 18, 20 accepting liquids thereby permitting evaporation and run-off of the liquids from the unit 12. A framework of ribs 22 is provided on the underside of each unit 12. Locating means may be provided on the ribs 22 in the form of spikes 24 or alternatively feet 224. The locating means are shaped to engage the ground beneath the unit 12 substantially without causing damage thereto. A plurality of ports 28 extend through the unit 12 enabling plants beneath the unit 12 to breathe. The ports 28 and recesses 18, 20 are of a size to be bridged by footwear.