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Australian Plants for Clay Soils

Many gardeners regard clay soils with disdain, believing that nothing will grow in them. However, although they can be difficult to work with, clay soils are usually quite rich in nutrients and can sustain good plant growth.

You need to understand how to work with clay soils, and choosing the correct time is the key.

Preparing clay soils

Clay soils should be prepared when the soil is just damp.

Clay soil should never be worked while it is wet, as this destroys the structure of the soil leaving great lumps of mud. When dry these become hard and unworkable.

Likewise, a clay soil should not be worked when very dry, for this also destroys the soil structure, turning it into a dust bowl.
A rotary hoe should not be used to work clay soils because the rotating action of the
tines will create a hard pan beneath the worked surface. A rotary hoe should only be used when mixing an introduced soil in with existing soils.
Once a clay soil has been broken up, and not compacted by machinery, it will remain in a condition conducive to good plant growth.

Adding gypsum to clay soil

Applying gypsum to the soil will not only improve the soil structure, but also allow air and water movement within the soil profile.
Gypsum works by binding the tiny clay particles together to form larger particles. However, gypsum is not stable in the soil, leaching down through the soil, requiring further applications every 4 or 5 years, depending upon rainfall and watering.

Adding organic material

Adding generous amounts of organic material to the soil will improve the workability of ALL soils.

Soil microbes such as bacteria and fungi will improve the soil structure by changing organic matter into humus.
Humus provides valuable nutrients for plants.
Plant diseases may be reduced by the addition of organic material to the soil.
Improve the quality of your soil by adding lots of organic material once or twice a year.

When selecting organic material, remember, if it has once lived,
it can be returned back into the soil.

Plants that will grow in clay soils

Astartea fascicularis 1 x 1.5m. Small leaves, white or pink flowers throughout the year.

Banksia ericifolia 5 x 4m. Rounded dense shrub, long cylindrical orange flowers during autumn and winter.

Banksia ‘Giant Candles’ is a cross between B.ericifolia and B.spinulosa. The orange flower spikes can be up to 40 cm. long.

Banksia spinulosa 1.5 x 1.5m. Cylindrical orange-yellow flower spikes during autumn and winter. Bird attracting.

Banksia spinulosa

Banksia robur

Banksia robur 2 x 2m. Large tough leaves with serrated margins, flower spike is blue-green in bud and yellow–green when in flower.

Banksia marginata 4-6 x 2-4m. Dark green leaves with a silver underside. Yellow flower spikes during spring and summer.

Bauera rubioides 1 x 1m. Rosy pink flowers for most of the year with a main flush in spring. White flowered forms are available.

Boronia denticulata 1 x 0.6m. Aromatic foliage, star pink flowers in spring.

Brachyscome multifida 0.5 x 1.5m. Small blue or white flowers throughout the year. Soft divided leaves.

Calytrix tetragona 1 x 1m. Bright green foliage. White through to deep pink star

shaped flowers in spring followed by reddish fruiting capsules.

Correa alba 1 x 1.5m. Oval greyish leaves. Open star shaped flowers in winter with some flowering throughout the year. Suitable as a front line coastal plant.

Correa ‘Dusky Bells’ 0.5 x 2.5m. Showy pink bell shaped flowers in autumn.

Correa ‘Mannii’ 0.5 x 1.5m. Dusty pink flowers in autumn and winter . Dense growth habit.

Correa reflexa 1-2 x 1-2.5m. Many forms available. Green through to red bell shaped flowers during autumn and winter.

Crowea exalata 0.8 x 0.8m. Aromatic foliage. Pink or white star like flowers in summer and autumn.

Dianella revoluta Flax-like leaves. Bright blue flowers in spring followed by deep blue globular fruit.

Eremophila maculata ‘Aurea’ 1.5 x 1.5m. Suitable for hot dry position. Yellow tubular flowers for most of the year .

Grevillea x gaudichaudii 0.3 x 3m. Vigorous groundcover with oak shaped leaves. Tooth-brush like deep red flowers in winter and spring .

Grevillea ‘Honey Gem’ 4 x 4m. Large shrub with orange toothbrush like flowers for most of the year. Bird attracting.

Grevillea ‘Moonlight’ 4 x 3m. Large shrub. Attractive cream toothbrush-like flowers.

Grevillea ‘Poorinda Royal Mantle’ 0.3 x 3m. Vigorous groundcover. Dark red flowers in spring and summer. One of the best ground cover grevilleas.

Hardenbergia violacea Trailing plant 1 to 3m. Can be used as a climber to cover fences etc. Purple, pink or white pea–shaped flowers in spring.

Hibbertia scandens Quick growing twining plant. Large yellow open flowers in spring.

Melaleuca hypericifolia 2 x 4m. Dense shrub. Brick red bottlebrush flowers in late spring and summer.

Melaleuca thymifolia 0.6 x 0.6m. Small shrub with elliptical leaves. Mauve or white flowers for much of the year.

Micromyrtus ciliata 1 x 1m. Very tiny green leaves. In spring the plant is covered in small white flowers. Suitable for cut flowers.

Myoporum parvifolium x 1.5m. Dense ground covering plant. Green or purple leaf forms, with white or pink flowers are available.

Prostanthera rotundifolia 1.5 x 1.5m. Roundish leaves often with toothed margins. Masses of purple flowers in spring. A pink flowering form is available.

Scaevola ‘Mauve Clusters’ Prostrate x 1.5m. Quick growing ground cover.

Westringia fruticosa 2.5 x 2.5m. Blue-green foliage. White flowers throughout the year. A hardy front line coastal plant.

Xerochrysum bracteatum syn. Helichrysum bracteatum ‘Dargon Hill Monarch’ 0.6 x 0.6m. Large grey-green leaves. Large flower heads in spring, summer and autumn. Bright yellow through to white everlasting flowers.

Produced by the Australian Plants Society, Central Coast Group in conjunction with Gosford City Council and Wyong Shire Council.
Australian Plant Society, Central Coast Group Web site: www.australianplants.org