Alan Titchmarsh and Joe Swift take viewers around the floral world as part of Chelsea's celebration of the International Year of Biodiversity. There's an entertaining journey through plant species from northern coniferous zones to the tropical rainforests, including a visit to South Africa's famous Kirstenbosch botanic gardens to see the stunning proteas that have been grown for Chelsea. Alan chats to some of the UK's celebrity visitors pledging support to the International Year of Biodiversity.