The aromatic boronia belongs to the rue family (Rutaceae). These evergreen shrubs are compact and small to medium-sized. All 140 odd species are endemic to Australia. The leaves may be simple or pinnate. The four-petalled flowers are small and often fragrant. Flower shape varies from open and star-shaped to bell-like with overlapping petals. Colours range from white, bluish mauve, brown, yellow, yellow-green and red.
Boronia alata grows to 2 metres and is endemic to south-west Western Australia. The leaves consist of 7 to 15 glossy leaflets. The edges of the leaves are irregularly serrated and the white to pink flowers are star-shaped. They may reach up to 25mm across and appear mainly in winter through to early summer. It can be grown in seaside gardens.
Native to the ranges and coastal areas of south-east New South Wales is Boronia barkeriana, a small shrubby bush. The simple leaves are dark green and the flowers form in small clusters of star-shaped blossoms from spring to summer.
Boronia megastigma or brown boronia is native to Western Australia. It can grow to 2 metres and is widely grown for its highly fragrant, small open bell flowers which appear from July to November. It is commonly brown to reddish-brown outside with yellow or lime-green interior. Sometimes the flowers are burgundy or lime-green. It is best suited to moist soil with relatively good drainage. The roots should not be allowed to dry out. Although it prefers semi-shade or morning sun only, it will grow in full sun. It is frost-tolerant.
A dwarf form of boronia is Boronia filifolia, also known as the slender boronia. It is native to Victoria and South Australia. It is a dwarf shrub with slender leaves which tend to be purplish in colour. Flowers appear mainly from August to January. The pink flowers are about 1cm in diameter. This species likes well-drained soil in partial or filtered sun. It responds well to regular light pruning.
Boronia floribunda (pale pink boronia) comes from the Sydney region of New South Wales and is also found in the Blue Mountains. It has reddish stems and dark green pinnate leaves. The pale pink flowers have a beautiful fragrance and appear in prolific clusters. If under cultivation, it needs good drainage.
Boronia serrulata is sometimes called the Australian native rose. It is a small shrub often with few branches and is confined to the Sydney district of New South Wales. The rich green leaves are diamond-shaped and the fragrant, bell-shaped flowers are a vivid pink. Although very attractive and an excellent cut flower, it is difficult to cultivate.
Boronias need to be positioned in a protected position, sheltered by other plants in full sun or semi-shade. Well-drained soil that has a relatively high organic content is best. Potted specimens will not do well in soil with a high phosphorous content. Do not let the plant dry out and, after flowering, trim the branches to half their length to improve the shape of the bush.