Boronias are perhaps the most obvious of all scented natives. There are approximately 70 to 80 species of boronia and all are Australian plants.
Most are small shrubs, all have some scent in the foliage, but only a few have highly perfumed flowers.
Given the right conditions and care, Boronias are lovely shrubs, whether it be for their magnificent perfume, aromatic foliage or attractive flowers.
Leaves are opposite, simple or pinnate, with oil glands (seen as small spots); scented foliage and/or flowers; clusters of colourful flowers with petals forming a cup (not as flat or opened as citrus).
The best soil is sandy or loose and good drainage is a must. Light requirements vary between the species, but generally overhead shelter from both the sun and frosts is important. They require protection from both hot and cold winds.
Some boronias can be difficult to grow being particular in their requirements for drainage, fertility, soil acidity, light, protection and moisture. Avoid lime and nitrogen fertilisers. The roots must be kept moist, but not wet (root rots can be a problem). Plenty of water should be provided in summer, on the foliage as well as the soil. They require a cool root-run as too much variation in ground temperature seems to disturb them, and they resent too much heat. Root disturbance can be very detrimental, therefore cultivation close to the plants shallow roots should be avoided. In drier areas of the country, permanent semi-shade is needed for most species.
Cultivation requirements are also quite specific. A mulch of leaf-mould or some other acid organic material once the plants are established is beneficial. This helps to retain moisture and keep a cool root-run. All mulches should not be allowed to make contact with the stem otherwise fungal infections such as stem rot could be a problem. Very light applications of genuine Blood and Bone or thoroughly rotted farmyard manure should be made at intervals. A fairly heavy pruning of strong plants should be made after the first flowering and a consistent light pruning undertaken after flowering in subsequent years. If flowers are being cut regularly for floral arrangements this should suffice.
Boronias are not generally long-lived plants, up to ten years is a maximum, but usually most species are good for only 2-4 years. Old plants tend to become woody and unkept and are best replaced. Propagation of most species is generally easy by tip cuttings in late summer. Some can also be grown by seed planted in Spring.
B. denticulata -upright habit to 2m tall, pink flowers all year, one of the hardiest.
B. filifolia -to 50cm tall, and spreading to 1m diameter; pink flowers all year, prefers a cool, sunny spot.
B. heterophylla (Red Boronia) -to 2m tall, upright, red spring flowers, likes a well drained, mulched position, one of the most commonly cultivated species in south eastern Australia.
B. megastigma (Brown Boronia) -to 1m X 1m, perhaps the most commonly cultivated species, brown flowers in early spring, excellent cut flower, but short lived.
B. mollis -to 1.5m tall, bright pink flowers, soft, divided foliage.
B. muelleri -to 50cm X 50cm, Pink flowers in spring, fern like foliage.
B. pilosa -to 1m tall, upright habit, pink spring flowers, soft foliage.
B. pinnata -to 1.5m tall X 1m diameter, bright pink flowers.
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