Laravel 5.1 How to join two collections of objects

All warehouses tables have differemt number of columns. So I can't use union inside a query. But I hate this way to join this collection of objects. There is a better (clear) way? Thx :)

public function index()
{

    $warehouses1  = Farm_warehouse::all();
    $warehouses2  = Butchery_warehouse::all();
    $warehouses3  = Grape_warehouse::all();
    $warehouses4  = Iron_warehouse::all();
    $warehouses5  = Rice_warehouse::all();
    $warehouses6  = Silk_warehouse::all();
    $warehouses7  = Wood_warehouse::all();

    $warehouses2 = $warehouses1->merge($warehouses2);
    $warehouses3 = $warehouses2->merge($warehouses3);
    $warehouses4 = $warehouses3->merge($warehouses4);
    $warehouses5 = $warehouses4->merge($warehouses5);
    $warehouses6 = $warehouses5->merge($warehouses6);
    $warehouses = $warehouses6->merge($warehouses7);


    return view('warehouses.index', compact('warehouses'));

}

via Chebli Mohamed