Boronia

( bo - ROH - nee - uh )

At-A-Glance Information

Boronia, commonly called Scent Leaf, is a genus filled with species of evergreen shrubs that need full sun to light shade and regular waterings for best performance in the garden. They produce clouds of pink, white, or mauve fragrant flowers against wispy-looking foliage. Species are native to Australia. Use Boronia in mixed beds and borders, for their cut flowers, or in containers. Care must be taken when planting these shrubs around your yard, as the leaves can cause contact dermatitis in sensitive individuals.

Boronia Species and Varietals

The genus Boronia includes around 160 species and is included in the family Rutaceae. It is named for Francesco Borone (1769 - 1794), an Italian naturalist and plant collector. It was first described by James Edward Smith in the publication Tracts Relating to Natural History. Boronia growing zones vary by species. For more information, see the species descriptions below. To find your zone, click here: Zone Map.

Boronia alata (Winged Boronia)
Endemic to southern Australia, these shrubs reach up to 8 feet tall (or shorter in more exposed sites), and produce pinnate compound green foliage. Flowers are pink to white in color and star-shaped. This species makes a fine ornamental plant in the garden. Winged Boronia grows well in USDA hardiness zones 9b-11.

Boronia clavata (Heather Wand, Club-Headed Boronia, Yellow Boronia)
This variety grows best in USDA hardiness zones 9a-11b or Sunset growing zones 15-17 and 19-24. This shrub can get to 4-6 feet tall and wide. Leaves are light green and aromatic, flowers are greenish yellow and lightly scented. Grows best in partial shade, and can be used as a screening plant.

Boronia crenulata (Aniseed Boronia)
Aniseed Boronia grows well in USDA hardiness zones 9a-11 or Sunset growing zones 16-24. Individual plants reach up to 2-3 feet tall and 3-4 feet wide at maturity. Leaves are small and dark green, and flowers are small and light pink and appear in late winter and spring. Varieties include 'Rosy Splendor' (a more upright grower), 'Shark Bay' (also called Shark Bay Aniseed Boronia, a compact plant with licorice-scented leaves and pink flowers that appear year-round).

Boronia denticulata (Mauve Boronia, Toothed-Leaved Boronia, Toothed Boronia)
This species grows best in USDA hardiness zones 9-11 or Sunset growing zones 15-17, and 20-24. Grows to reach 3-8 feet tall and 1.5-4 feet wide. Leaves are strongly aromatic. Flowers are mauve to pink, and at times white in some varieties. They bloom in late winter and spring, and sporadically throughout the rest of the year.

Boronia heterophylla (Red Boronia, Kalgan Boronia, Pygmy Lantern)
Grows well in USDA hardiness zones 9-11 or Sunset growing zones 16-24, and has a dense growing habit to 6-8 feet tall and 4-6 feet wide at maturity. Leaves are finely cut and blooms are profuse in deep pink with reddish buds. Bloom time is late winter and spring. Intensely fragrant plant. Cultivars include 'Red', 'Moonglow', 'Cameo', 'Lipstick', and 'Blue Waves'.

Boronia megastigma (Brown Boronia)
Grows best in zones 15-17 and 20-24, this is a more compact variety growing to about 2 feet tall and wide with bell-shaped deep red to brown flowers with yellow interiors. Blooms in the wintertime. This plant has a powerful fragrance. Plants will need replacing every two or three years. Cultivars of this species include 'Jack McGuire's Red' (with deep red to orange blooms), 'Lutea' (with yellow flowers), 'Harlequin' (with striped yellow and brown flowers), 'Hot Chocolate' (with chocolate-colored blooms), and 'Heaven Scent' (with a stronger scent than the straight species).

Caring for Boronia

Plant Boronia shrubs in a space in the landscape that receives full sun to light shade; ideally, they appreciate between 6 and 8 hours of sun each day for the best blooms. There are some species that can take a bit more shade; make sure to check growing instructions for the species before installing. Ensure that soil is well-draining, rich in nutrients, and has a pH of between 5.5 and 6.5 (slightly acidic). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water new plantings regularly as they establish a strong root system in their new home. At maturity, these plants perform well in consistently moist soils. Roots should never be allowed to become completely dry or sit in standing water for too long. As a general rule of thumb, water whenever the top two inches of soil feels dry to the touch.

Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. Pruning is simple; remove any damaged, diseased, or dead foliage at any time during the growing season. A light pruning can be completed after blooms fade to encourage a more bushy, less leggy habit and to rejuvenate the plant and promote more new foliage growth. The average lifespan for most Boronia species is between 2 and 3 years, after which they will need to be replaced (though some species can survive for 5-10 years).

Caring for Boronia in Containers
Boronia shrubs are wonderful in the ground, but can also be grown in containers. Choose a container that is at least a few inches wider and deeper than the nursery pot or root ball. Ensure that the pot has adequate drainage holes on the bottom to allow for excess water to flow away. Fill with a well-draining potting mix amended with organic material and perlite, and top with a layer of mulch to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water regularly as the plant establishes itself in its new home. Once established, waterings can be lessened, but soil should be kept consistently moist. As a general rule of thumb, water whenever the top inch of soil feels dry to the touch. Boronia plants grown in containers will need more frequent irrigation than those grown in the ground. Prune to remove dead, damaged, or diseased foliage at any time during the growing season. Every few years, check the bottom of the pot to ensure that the plant is not outgrowing its root space. If roots are growing through the drainage holes in the bottom of the container, it is a good indication that it needs to be potted up; choose a slightly larger container and repot.

Propagation

Boronia plants can be propagated either through cutting or through seed. Cutting is the preferred method, however, given how difficult it is to both collect and germinate Boronia seeds. To propagate Boronia by cutting, follow these instructions:

Propagating Boronia by Cutting

Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with potting soil. A good substrate for propagation of cuttings is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
In spring or summer (May to August), before the plant has had time to harden its current season's growth, choose your plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 4-6 inch portion(s) of the end of a non-blooming branch and strip off all of the lower leaves, leaving the top two on the cutting. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot.
Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in cool, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about two months have passed, your cutting should be rooting. When you notice new growth on your propagated Boronia, you'll know you have roots.
Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, for about 18 months, after which your new Boronia will be ready to be planted in its new home in your garden.