In September to October Canberra hosts what is now Australia's largest floral festival - called Floriade. Held in Commonwealth Park, there are millions of tulips, annuals and every type of flower proudly on display.
And another place that's not exactly in Amsterdam: Floriade 2012 in Venlo. It's a horticultural expo taking place every 10 years, each time in a different city. Holland's a tiny country though, so maybe worth a visit when in The Netherlands.