Sometimes known as the floss flower, this Ageratum is a tough plant from Mexico that forms a mound 60 cm or more wide and about 30 cm in height, with curious soft blue-lilac, fluffy flowers. Ageratum is often grown as a dwarf annual (which is something of a weed) but this perennial form has been grown in our Sydney region for a long time. It takes root where it touches the ground and seems to flower all year round. It flowers best in sun, in well-drained soil. Occasional deadheading of the spent blooms will prolong the flowering period. I also prune it back occasionally and pull up any stems that have wandered too far. Tip-pruning in spring is very beneficial in promoting a bushy shape; it can get a bit straggly otherwise. It is like a miniature version of the shrubby Mexican Eupatorium megalophyllum (ht 1.5 m), which flowers in August. Ageratum and Eupatorium are both unlikely members of the Asteraceae family of plants - though they don't look like most daisy flowers! Both have nectar-rich blooms that attract butterflies.
Postscript: Eventually, I removed this plant from my garden as it seemed to be subject to a pest or disease that made the leaves curl up. It also needed constant deadheading, as the spent flowers were unattractive. I loved the colour of the blooms, however, and now have a replacement for them in the form of the beautiful, long-flowering Plectranthus zuluensis!