This species used to be classed as a subspecies of Hydrangea macrophylla. They are often colloquially known as 'lacecaps', because the cultivars have this type of inflorescence (with flattish flowerhead comprising a few large sterile flowers surrounding many smaller fertile flowers), but H. macrophylla also contains some lacecap cultivars. H. serrata plants are usually quite compact, with narrowly ovate, pointed foliage. The flowers are smaller than those of H. macrophylla. Their height is usually around a metre or a little more. The stems are usually much thinner than the more robust-looking H. macrophylla shrubs. Flowering commences in late spring and continues into summer, but for a shorter period than that of the H. macrophylla types. The species is found in the wild in Japan and Korea; most of the available cultivars are of Japanese origin. 'Grayswood' is an attractive cultivar, with white sterile flowers that turn dark pink-red as they age (even in acid soil like mine!). 'Blue Deckle' is a pretty blue cultivar. Acid soil conditions (below pH 6.5) are needed for blue flowers, as with all Hydrangea. There are white-flowered cultivars, although I have never seen them myself.
These shrubs grow quite well in Sydney gardens, as well as in cooler areas. Because they are compact, they can be grown in large pots.They grow best in part-shade with some morning sun but protection from hot afternoon sun. They need reasonable soil and adequate moisture, especially in their early years, but not boggy soil. It is beneficial to provide an annual mulch of garden compost to help maintain soil moisture. These plants seem to have few pests or diseases, though fungal problems can occur in the leaves during the humidity of summer. The worst leaves can be picked off - don't compost them, however. Sometimes leaves may seem distorted, but this is due to sudden spells of heat in spring. Mildew on the leaves may occur if the plant is grown in a very dry shaded position. Red spider mite can be a problem - insect predators can be used to control them, if required. It is best to prune this type of Hydrangea in February, cutting the whole plant back by about half - otherwise you will get few flowers. Feed well after pruning and again in late winter. Osmocote can give good results. Hardwood cuttings can be taken in winter - they will take a while to strike but will eventually form new plants. It is also apparently possible to take tip cuttings in summer or to layer stems.