Daylilies must be one of the plants with the most cultivars in the world! There are more than 50,000 registered cultivars of these perennials (many with rather bizarre names, such as 'Crocodile Smile' and 'Pardon Me'!). The original species come from China and Japan, and number around twenty-six; their flowers are mainly in the yellow to orange colour range. Some of these are still worth growing, such as double orange-flowered Hemerocallis fulva 'Flore Pleno' (which is said to tolerate some shade, unlike most other daylilies) and fragrant, yellow-bloomed Hemerocallis lilio-asphodelus . Nowadays, every possible colour daylily has been bred (except for absolute pure white and true blue), which gives amazing scope for creating colour schemes in the garden. Flower sizes vary from true miniatures (less than 7.5cm across) to large-flowered ones 11cm or wider. Flower shapes also vary, from the basic trumpet shape to elegant spidery-looking ones, star-shaped, triangular, full circle formations and doubles. Many have contrasting coloured 'eye-zones' and throats, which give a dramatic look.
As their name implies, the flowers are open only for a day. However, this is offset by the sheer number of blooms that can occur on a well-established clump, providing colour over a long period. Spent blooms can be quickly snapped off each morning as you admire the fresh crop, and this will improve the appearance of the plant and give the newly opening buds room to expand. There are early-, mid- and late-blooming varieties, with the peak display being around November and early December in Sydney. A lovely orange-red one I have called 'August Flame' flowers around January. Some will re-bloom in autumn, particularly if watered and fertilised regularly in summer.
The foliage of daylilies is basically a clump of strappy, arching leaves. There are evergreen, semi-evergreen and deciduous types. In general, the evergreen ones seem to do best in the Sydney climate; the more deciduous types are better in cooler climates but are worth a try here if you are really keen.
Easy to grow, they enjoy a sunny, well-drained position in soil improved with organic matter. A little lime is said to be beneficial - if your soil is inclined to be on the 'acidic' side. Daylilies dislike competition from nearby tree or shrub roots and they may rot off in very poorly drained soil. The crown should be at soil level; planted too deeply, it may rot. Water well for the first few weeks until they become established. It is possible to grow them in containers, especially the lower-growing cultivars, with the optimum pot diameter being around 30cm. They do appreciate some regular water during their growing season; though they cope with dry spells very well, flowering will not be as prolific. Keep the plants well mulched to retain moisture and minimise weeds, but don't let the mulch touch the crown of the plant or it may rot.
Daylilies respond well to fertilisers applied in September and again in March. Occasional applications of liquid fertiliser will be beneficial in between times. The clumps can be propagated by dividing the fleshy roots every three years in autumn or winter, and replanting in fresh soil, as flowering will be affected when the clumps become too congested. The clump can be dug up completely, or a serrated knife can be used to saw the clump in half and then one-half of it can be lifted and divided. The leaves can be trimmed in mid-winter if looking scruffy. Some growers cut these off completely in June.
Aphids can be a nuisance in spring, especially if the plants are stressed, and these should be tackled with horticultural oil or even soapy water, before they get out of hand and significantly reduce the vigour of the plant. Thrip can be controlled by overhead watering of the plant. Slugs and snails may also ruin the foliage, so need to be guarded against. A new threat to daylilies is a rust, which as far as I know, has no known cure yet. I have had reasonable success with removing the affected foliage at ground level and getting rid of it in the rubbish bin. The new leaves tend to grow without the rust, at least for a while. Organic fungicides can help, as can avoiding watering the plants in the afternoon or evening.
I think that the larger-flowered daylilies look best in gardens with shrubs or with warm-climate perennials (such as Salvia, Dahlia, Canna and Agapanthus), as their flamboyance and brilliant colours do not meld quite so well with dainty cottage garden planting schemes; miniature-flowered daylilies work better with these. Two reliable miniatures for the Sydney climate are bright red 'Crimson Icon' and orchid pink 'Siloam Bo Peep', which has a purple eye-zone. Daylilies, especially the spidery-looking ones, also associate well with ornamental grasses and prairie-style plants.