I gave a talk on this topic in Kuching a couple of days ago, and this is a brief summary.
The everflowering garden can only be created where it is warm and moist all the time, as in the humid tropics. The British had a go at it when they ruled what is now Malaysia and Singapore, but most of the flowering plants they used were annuals imported as seeds from Britain. In front of their bungalows, the British created lawns fringed by borders of flowering plants. The lawn tradition survives but the flowering border could not be sustained. By default, gardens in the humid tropics are evergreen--monotonously so! However, in the past 50 years, more and more tropical perennial ever-flowering plants have come into existence. I counted over 100species in my book Tropical Horticulture and Gardening. The ever-flowering garden is now well within reach and should be one of the aims of tropical gardening.
50 years ago, it was a problem to keep bougainvilleas in flower. Now there are ever-flowering bougainvilleas in a wide range of colours, thanks of plant breeding and selection. Other plants that have become ever-flowering are the drunken sailor Quisqualis indica and Kock's bauhinia Bauhinia kockiana. New forms of Hibiscus, all ever-flowering, have been bred in Hawaii and Australia. Ever-flowering heliconias have become common. Ever-flowering Canna were bred by the late Professor Holttum in Singapore but most of these have been lost; we have to start all over again.
I am particularly keen on cannas because they are easy to breed and select. I distributed hybrid seeds in Kuching and encouraged my audience to form an informal club for future breeding and dissemination of seeds. The breeding and selection of cannas will be my next blog.