A shrub growing usually to about 1.5 metres tall.
It has a comparatively small natural distribution, growing between Gosford and Wollongong, close to the coast with a gap in the middle of Sydney.
It is found in moist heath and dry sclerophyll woodland on Hawkesbury Sandstone.
Boronia spp. produce opposite leaves which can be simple or compound (sometimes on the same plant) and are usually aromatic (sometimes strongly-so).
In this species, leaves are crowded and sessile along the stems, strongly aromatic, broad-obovate to elliptic, to about 2 cm long and to 1 cm wide with margins finely but obviously toothed.
Boronia spp. have complete flowers (bisexual and with all whorls present). The flowers are produced either solitarily or in groups, in the leaf axils, or, at the branch terminals. There are usually four sepals, four petals and generally eight stamens, surrounding one female part (carpel). Flowers are often pink to purple, which makes them easily identifiable in NSW bushland.
In this species, inflorescences are produced at the terminals, solitarily or in up to groups of 4, bright to deep pink, about 2 cm across and very showy, usually in winter-spring.
The fruit of Boronia are described as a schizocarp-capsule; a capsule that splits into even segments, which each segment called a coccus. In this species, the cocci are in a cluster of 4, producing dull or shiny black seeds.
Makes an excellent specimen plant and performs well as a cut flower.
Has very fragrant flowers and is a useful feature plant but may be short lived.
In a garden situation B. serrulata should be grown in well-drained soil, in a raised rockery. Some authorities suggest placing some sandstone rocks placed around the root zone to give the plant a cool root run. It has been cultivated with some success.
Leaf-eating caterpillars and root rot sometimes affect this species.
Growing boronias can be a frustrating experience and they have a reputation for being difficult. Their attractiveness has led to substantial efforts to cultivate them. One tip is to try to grow forms that are local to your area, rather than attempting to grow those species from interstate. There are certainly some species that have proven easier to grow than others.
Most boronias have a short life span of two to three years in a garden situation but are a rewarding plant while healthy as they provide lovely fragrance and flowers in Spring.
For them to grow at their best, select a position with dappled sunlight and especially protection from hot afternoon sun in summer, as well as from wind, which they dislike.
The soil must be well drained and have an even supply of moisture. These plants are likely to die if they dry out too much.
Planting on a slight slope is said to work well.
For a longer life, the best way to grow them is in a medium sized pot, say 30 cm in diameter where drainage and moisture can be controlled. A sheltered patio or courtyard that receives at least a few hours sunlight a day would be ideal.
Fertilise after flowering.
The conventional wisdom is, think deeply about which species to plant and the location to plant it.
Propagation is by semi-hardwood cuttings taken in early summer. Boronias can be propagated from cuttings but with limited success with most but not all species.
Boronia is a genus of about 150 species in the citrus family Rutaceae. Most species are endemic to Australia and species can be found in all states. There are also 4 species in New Caledonia, which were previously placed in the genus Boronella. In 2020, several species of Boronia have been transferred to the genus Cyanothamnus (meaning “blue shrub or bush”), as these species have been found to be more closely related to other Rutaceae genera rather than other Boronia species. After the move of some species to Cyanothamnus, there are about 30 Boronia spp. in NSW.
Boronias are likely killed by fire and regenerate from the seedbank.
Boronia – after Francesco Borone (1769-1794), an 18th century Italian botanist who assisted John Sibthorpe. Allegedly, he died at age 25, due to falling out a window whilst collecting plant specimens.
serrulata – from Latin, serra, meaning “a cutting saw” – a reference to the fine serrations on the leaves.
This species is not considered to be at risk of extinction in the wild.
Australian Native Plants Society Australia – Boronia Family Profile Page
Gardening with Angus Website – Boronia for Beginners
Australian National Botanic Gardens – Boronia serrulata Profile Page
NSW Flora Online (PlantNET) – Boronia serrulata profile page
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.