Napier Grass

Pennisetum purpureum, the Napier Grass or Elephant Grass, is a giant African cane grass reaching 2 to 4 metres in a season, with broad arching leaf blades that are green in the agricultural forms and purple-bronze in the ornamental selections.
It is the fastest screening plant in the grass palette, used to close a boundary or hide a compound within months rather than years.
Napier Grass is the quickest green screen available, on the understanding that it needs an annual cut to stay where it was put.