Euphorbia characias subspecies wulfenii is a shrubby perennial growing to about 1 m, with blue-green leaves. In late winter and spring it has stunning rounded heads of acidic lime-green bracts, which last for a long period. A Mediterranean plant, it needs a sunny, well-drained position. It combines well with other Mediterranean plants which grow in Sydney, such as French lavender Lavandula dentata, tough purple flag irises (the original Iris germanica), perennial statice (Limonium perezii), Pride of Madeira (Echium candicans), rosemary, perennial wallflowers (Erysimum mutabile) - which all enjoy the same garden conditions.
This Euphorbia should be pruned back after flowering, when new foliage growth can be seen emerging at the base of the plant. Where it is happy, it may self-seed. Cuttings can also be tried - the best time may be in winter. Many of the Euphorbia genus do not thrive in Sydney, but this one can, given the right conditions. After a few years, it may get woody and tired, which may be the time to replace it with a seedling or cutting. A new cultivar, 'Silver Swan' (ht 50 cm, pictured above), has white and green variegated foliage and white flowers; however, I have found it not particularly successful in my Sydney garden for very long.
All Euphorbia have an irritant sap in their stems so take care when handling these plants and always wear gloves when pruning. Be very careful not to get any sap in your eyes as this can cause damage to them. It is also prone to self-seeding so be sure these don't escape into bushland areas.