Each flower blooms for but a day, hence the common name daylily, and the scientific name Hemerocallis , which in the Greek means something like "beauty for a day." But each spike can hold as many as a dozen blossoms that open one after the other, and a healthy clump may produce as many as two dozen spikes.
So though the individual flowers last but a day, daylilies seem to be in flower all summer long.
Daylilies are one of summer's most reliable perennials, coming into bloom as spring's flowers fade. The common lemon yellow is an almost indestructible plant, used even in freeway plantings, but all daylilies are tough, and easy to grow. They stand the heat of the inland valleys, and some actually require it (the reds especially). And they're bothered by few pests (but watch for snails in coastal gardens). In the hottest areas, they may look best facing east, where they receive afternoon shade, and in all areas they easily tolerate a half day of shade, much like agapanthus.
Their arching, fountaining foliage can be the backbone of any perennial garden; so avoid the few deciduous kinds. The flowers will stand well clear of the foliage on sturdy stems though they look more dramatic against a dark background. Most grow three to four feet tall, in clumps as wide, but there are also useful miniatures and in-betweens for smaller gardens.