How mulching and canopy architecture interact in trapping solar radiation inside a Mediterranean greenhouse

•Representative ground (ag) and cover (ac) albedo was measured in unheated greenhouses.•Plastic and gravel-sand mulches substantially influenced ag and ac of greenhouse crops.•Greenhouse crops grown with high-wire systems presented lower ag than outdoor crops.•A model for ac estimation was assessed and used to evaluate the influence of ag on ac•Extensive Mediterranean greenhouse areas might increase the global albedo regionally.