Like many plants which do well in Sydney gardens, Agapanthus are native to South Africa. They are currently classified as belonging to the Amaryllidaceae family of plants.The big rounded umbels of mid-blue or white flowers appear on 1 m stems above the strappy leaves in late November and bloom all through December, providing lots of material for floral arrangements at Christmas time. The most commonly seen species is Agapanthus praecox .
They enjoy a sunny, well-drained position (with boggy conditions being fatal for them) and can grow in very harsh, deprived situations, providing a refreshing sea of green leaves where few other plants will thrive. They can also do reasonably well in part or dappled shade but will not flower as profusely as they do in sun. They can also be used to provide a bank of lush green foliage in a shaded spot! where little else will grow! However, they shouldn't be just used as a desperation measure in gardens: they have much more to offer than that.
Their foliage forms an excellent groundcover and they can also be used as a low border along a driveway or fence. The bold flower-heads make them probably more suited to a semi-tropical style or shrubbery garden than dainty cottage gardens. They mix well with summer-blooming Salvia, providing a good contrast of flower form, or with lush Dahlia and Canna cultivars. The many colours of daylilies (Hemerocallis), which are in bloom at the same time, provide a range of possible combinations.
Agapanthus look very effective grown beneath deciduous trees and will cope well with root competition of, for example, Jacaranda. White versions of Agapanthus look wonderful grown with white-variegated foliage, such as that of Miscanthus sinensis 'Variegatus', or the silver leaves of Plectranthus argentatus; alternatively try them with purple-black foliage or flowers, to provide a striking contrast. Grown in an open spot with a background of Hydrangea shrubs planted in shadier sites, they will echo the shape and colour of those flower-heads which are in bloom at the same time, giving a pleasant coherence to the garden.
Although they will thrive on neglect, a little attention will be repaid with better flowering, so it is worth throwing some fertiliser into your Agapanthus clumps when you are doing the rest of the garden, and giving them a little water in very dry times. They also like mulch around their shallow roots. They can be grown in pots, but will need repotting every year or so, as excessively pot-bound plants will flower poorly. Clumps growing in the ground can be divided in spring or autumn when they get too thick - every four to six years; this will improve flowering and is the best way of propagating them. Snails will congregate in the foliage, so use some sort of bait to control them; apart from that there seem to be no pests or diseases which worry them. The flower-heads should be removed before seeds form, as these may cause problems in bush land areas. Removing shabby old foliage in late winter makes the plants look better!
There have been some excellent cultivars developed over the years and there are now many shades of blue to choose from: the miniature 'Peter Pan' with narrow grassy foliage and milky blue flowers, which grows to only 45 cm; the tall, sultry 'Purple Cloud' (ht 1.8 m) and the stunning midnight blue 'Guilfoyle' (ht 1.5 m) are just some examples. 'Queen Mum' (ht 1.5 m) is a tall, robust cultivar with large white flowers that have a blue-tinged centre. They seem to be as tough as the original species. Agapanthus 'Amethyst' and 'Buccaneer' flower two or three times through the year; I haven't tried these myself. I have an attractive cultivar (possibly 'Zambezi') with cream-striped leaves and blue flowers. The foliage looks good all year round. There are a number of deciduous species, but these seem to do better in cooler climates than ours.