One reason why individual flowers remain in good condition for a long time is that they are not being pollinated. As soon as fertilization takes place, there is no need to attract more pollinators and the flower's showy petals often wilt and dry out. I also notice that the earliest-flowering Narcissus species here, such as Narcissus cantabricus and Narcissus romieuxii, are very persistent this way, but the later members of the same (Bulbocodium) section wither sooner. I don't have the early ones in the open garden. Continuous bloom with repeated production of newly opening flowers is probably a characteristic of certain species that have evolved where the mechanism of pollination is available over a long period but not reliable in all years. Annuals grown in gardens have been selected for this characteristic. It is also well known that sterile selections have longer-lived flowers, whether the sterility results from hybridization or from the absence of reproductive structures as in some double-flowered plants. You can see this especially in Paeonia, where the single-flowered true species have short-lived flowers. (Mine are all available to pollinators, so I don't know if non-fertilization would induce the flowers to "last" longer.) One way to get a longer season of bloom is to grow plants from different populations of a species. It is curious to see how seedlings from one place may flower several weeks before those from another. It is also annoying if you have only one clone from one of the populations and would like to get seed from it. Jane McGary Portland, Oregon, USA