Alkaline soils are reasonably common in Australia, particularly in the arid zones. There is no easy method to lower the pH of highly alkaline soils. Luckily there are a number of Australian native plants that are either native to, or are tolerant of, calcareous or alkaline soils.
The following list is certainly not exclusive but gives some idea of the native Australian plants that are worthy of cultivation, being highly decorative in the area of form, foliage, flowers and fruits and sometimes eye-catching in all areas.
Australia has a number of acacia species, more commonly known as wattles. Acacia calamifolia, also known as Wallawa, is endemic to New South Wales, Victoria and South Australia. It is a medium to tall shrub with long, narrow phyllodes. Profuse, golden, globular flower heads are produced from July to November. It requires a warm, well-drained situation and is drought and frost tolerant. It is useful as an ornamental and as a screen plant.
The Allocasuarina verticillata or Drooping She-oak (once known as Casuarina stricta) can grow to 11metres and has an erect trunk and dark, furrowed bark. The foliage is long, narrow and pendulous. Yellow-brown male flowers are produced during March to December. It is a hardy plant and suited to a wide range of conditions including exposed coastal conditions. It prefers a well-drained position but tolerates wet periods.
Baeckea behrii, or Broom Baeckea, is native to the inland districts of New South Wales, Victoria, South Australia and Western Australia. It grows to 2 metres and is a slender shrub with small, white, open-petalled flowers appearing mainly during August and September. It is drought resistant and prefers warm conditions but will grow in cooler climates. Occasionally a pink-flowered type is seen.
Brachychiton populneus has the common name of Kurrajong. When in bloom, it is a spectacular tree with cream or pink, bell-shaped flowers. Red markings are present on the inside of the flowers which appear mainly from October to February. It is widely used for shade and shelter and is popular as a street tree. Young plants are often grown indoors. It is resistant to frost.
The cultivar Callistemon ‘Harkness’ is an eye-catching specimen (to birds too!) with new leaf growth being a pink colour. The bright red flower spikes grown to 15cm long. The flowering season is mainly from September to January. It is a popular garden choice and adaptable to a wide range of situations. It responds well to pruning after flowering.
The cassias are a hardy species with many forms and hybrids. One that does well in alkaline conditions is Cassia nemophila or Desert Cassia. It grows to 3 metres and is a bushy shrub with green or silvery leaves. Clusters of yellow flowers are produced from June to November.
The Correa alba or White Correa grows to 2 metres. It is a dense shrub with oval, green leaves and sometimes rusty new growth. Starry white or (sometimes) pink flowers appear mainly during November and through to May. It is a hardy plant which tolerates moist or dry, well-drained soils and exposed coastal situations. It prefers full or partial sun and is not affected by frost.
Eucalyptus Maculata or Spotted Gum is often grown for its spotted, smooth-barked trunk. Prolific white flowers appear in May and June. It is hardy and adaptable, and makes an excellent shade and shelter specimen. It also attracts birds.
Moat grevilleas produce nectar which is sought after by birds and Grevillea lavandulacea is no exception. It is also known as the Lavender Grevillea . It is a variable species with greyish foliage and has clusters of bright pink to red flowers mainly from June through to November. It is adaptable, widely cultivated and prefers a warm, well-drained position. It responds well to pruning.
Templetonia retusa or Cockies Tongues is endemic to South Australia and Western Australia. It usually forms an upright shrub and has grey-green, wedge-shaped leaves. Showy, large bright pink or red (rarely white) pea flowers are produced from May to October and attract native birds. It prefers a relatively open position.
These are just some of the lovely Australian natives that will grow well in alkaline soils and give an eye-catching display throughout the year.