Monty Don continues his extraordinary journey to see the world through 80 of its most inspiring gardens.This week he travels to Australia and New Zealand, two of the youngest gardening cultures in the world. But it is not just about dreamy climates and wonderful plants. Monty sets out from the aptly named Botany Bay to uncover a story of culture clash and plant invasion, where the gentle habits of the indigenous people and the extraordinary natural landscapes have been dashed aside in favour of imported plants and a surprisingly English style of garden.By the time he finds his feet in New Zealand he's soon gasping for native plants and sets off in search of the wild heart of New Zealand, where he revels in a magical rainforest garden created entirely of native plants.