Soils

Understand your soil type

Soil type is a most important factor influencing which native plants you will be able to grow successfully, so it is essential to know and understand the soil types in your garden before starting to select and plant suitable native plants.

Our soils in Victoria are very diverse and it is possible in any one area to have many different soil types.

Soils are classified into a number of types depending on the particle size. Soil scientists define size classes as: gravel, sand, loam, silt and clay. Gravel particles are larger than 2mm and others go down in 10-fold jumps in fractions of mm.

Gravel	Course sand	Fine sand	Silt	Clay
>2mm	2mm	0.2mm	0.02mm	0.002mm

Most of us classify soil as gravel, sand, sandy loam, loam, clay loam or clay.

How to determine your soil type

One way is to take a sample to your local Department of Primary Industries office and have it analysed. Another method is to take a slightly moist sample in your hand and squeeze it: ...

Gravel or sand - Soil fails to compact and runs through your fingers.

Loam - Soil compacts slightly but still fragments through your fingers.

Clay - Soil remains as a solid mass.

Soil structure

Soil structure refers to the way soil particles are grouped together. The particles in most soils consolidate into fragments of various sizes. Some soils, such as beach sand, have particles which do not cling together and therefore have no structure. Some clay soils cling together in one solid mass but also lack structure. Well-structured soils break up easily into fragments with definite shapes and sizes. These fragments, being irregular in size and shape, do not completely fill the space they occupy and result in a net work of open spaces and passages which are filled with water, air and plant roots. In fact, an average soil may consist of 40 to 60% open space.

The structure of the soil is very important to gardeners. A well-structured soil will easily take in water through the spaces between the particles. Excess water will drain away through the spaces and be replaced by air. Most plants need air and water near their roots to grow well.

As many native plants have deep-penetrating roots, it is advisable to take a number of soil samples, one at the surface, another 200mm in depth and the last at 400mm in depth. Surface soils may contain a lot more humus and be much more friable than those underneath. A friable soil is one which can be easily fragmented or broken up. Friable soils allow easy cultivation. These soils contain varying amounts of all sizes of mineral particles, together with organic matter.

Will my soil support the plants I want to grow?

Having determined your soil type, the next objective is to decide what native plants you want to grow and find out what is the soil type in which they grow naturally. This is very important as some native plants are very particular about soil type and are difficult to grow in other types. For example, Banksias from Western Australia mostly grow in deep sand that has excellent drainage.

Soil type and structure are not the only considerations - Is your soil boggy, acidic or alkaline?

Plants that grow in boggy soils will grow in well drained soils provided adequate moisture is provided in dry periods, but the reverse will not work. Plants that grow in alkaline soils will grow in acid soils, but the reverse will not work. Most plants around the southern and eastern part of Australia grow in acid soils, however in inland Australia the soils are more likely to be alkaline.

A soil's degree of acidity and alkalinity is determined by measuring its "pH". pH measurements are expressed as a number on a scale from 0 to 14 where 7 is neutral, less than 7 is acid and greater than 7 is alkaline. Most soils have pH values between 3.5 and 10. In higher rainfall areas the natural pH of soils typically ranges from 5-7, whereas in drier areas the range is 6.5-9. Soils with pH values of 6.5 to 7.5 are referred to as ‘neutral’. Those with pH less than 6.5 are acidic, and soils with pH less than 5.5 are considered strongly acidic.

The acidity of soil can be reduced by adding lime or dolomite, and alkalinity reduced by adding sulphur. To ensure the desired soil pH level is maintained, these treatments may have to be repeated at regular intervals.

To determine the pH of your soil you can buy a soil pH testing kit, or take soil samples to your local Department of Primary Industries for analysis.
>> Broad-scale surface soil pH map of Victoria

Characteristics of different soil types

Gravels have little ability to hold water, retain fertilizers and are naturally very low in plant nutrient. They make an excellent mulch, however, it is difficult for plants to survive in them unless clay and loam are added to hold moisture and nutrients. Deep rooted plants from gravelly soils, once established, will survive in them, because moisture is often present at depth.

Sands have similar characteristics to gravel but do retain some moisture, especially as depth increases. Often sandy soils become more compacted as depth increases and tend to have more of a sandstone profile. Their drainage is excellent and many plants from sandy areas such as Western Australian Banksias have adapted to survive in these nutrient-deficient soils.

The top 100mm plus of sandy soils can be water-repellent due to wind-blown particles. This can be overcome by digging in humus, clay or loam soil to give a much better water retention profile. Alternatively, the top 100mmm plus can be removed from the proposed planting area to expose the more porous sand below. Soil wetting agents can also be used.

Near the sea, calcareous soils may be found which, due to their poor structure, accept very little moisture and it can be very difficult to establish a garden unless using local native plants.

Loams are often found where market gardens were once established. Much of south-eastern Melbourne, which is now built on, consists of these soils. Whilst they have good drainage they do retain some moisture and allow the roots of native plants to readily penetrate downwards. Many native plants can easily be grown in these soils.

Clays are heavy soils that can retain a lot of moisture, but when they dry out and crack they are hard to dig. They have plenty of plant nutrients.

To make clay soils more friable, add gypsum at a rate of 1kg. per square metre repeating the treatment at yearly intervals if necessary. Ripping the soil when the gypsum is added will help it penetrate further down, and adding sand and humus also helps improve friability. Many native plants grow well in clay soils.

Soil types across Victoria

It is not possible to detail all the soil types to be found across a geographic region as they are too numerous. Here we will deal with the major soil types. For more precise information on the soil types where you live, consult with your local APS Victoria District Group, obtain a soil map from your local Catchment Management Authority and check out information available on line from the Victorian Department of Primary Industries bioregions web site.
Soil profile photograph courtesy of the U.S. Geological Survey

The Mallee

Most of the area consists of sandhills overlying limestone deposits. The soil is alkaline and poor in nutrients. The low rainfall makes it difficult to grow plants other than from inland areas.

Along the Murray River the sands are more loamy and less alkaline and with the aid of irrigation water the range of native plants which can be grown increases. The summers are very hot with most of the rainfall occurring in the winter/spring period.
APS Victoria District Groups covering this region - Mildura

The Wimmera

Much of the region has been cleared for farming as the soils are generally heavier. The northern part merges into the Mallee sands and to the west the sandy country is much flatter, with some high ridges. The latter have more loam content in them and combined with a higher rainfall to 500mm, are able to sustain taller shrubs and trees. A large area of the Wimmera consists of heavy clay soils which have a higher proportion of sand grit in them, enabling the sowing of cereal crops, etc. Most soils are still alkaline and the climate consists of hot summers and wet winter/springs, although rainfall can be very erratic.
APS Victoria District Groups covering this region - Wimmera / Horsham | Grampians / Pomonal

Northern Country

This region stretches from the Loddon River in the west to Yarrawonga in the east. It is mainly flat with numerous streams traversing the country side. The soils are mainly clays but clay loams to loams can be found in fruit growing areas.

Along the major rivers there are some sandhill deposits which are excellent for growing Proteaceae species. The summers are hot and generally dry and the winter/springs wet, although the rainfall can be very erratic.
APS Victoria District Groups covering this region - Loddon-Murray / Kerang | Bendigo | Shepparton

North Eastern Region

There is a great variety of soil types here as the region extends from the flat country of the river systems as they flow north to the Murray River, to the alpine areas of Mount Hotham. Here are also the granite outcrops of the Warby Ranges, Strathbogie Ranges and the ranges of the Beechworth and Cudgewa areas. The lower slopes of these ranges often have deep loamy soils with underground moisture.

The flat country is generally made up of clay soils but as the streams head back into the hills, better clay loams appear.

East of the Strathbogie and Beechworth Ranges, the hills consist of richer clay loam soils and taller trees and shrubs occur. The rainfall is considerably higher. Also in the hills there are some volcanic outcrops of rich red brown friable clay loam soils which sustain lush vegetation.

The exposed alpine area is covered in snow in winter and consists of shallow soils in amongst outcrops of shales and schists. Below the snow line the soils become friable clay loams to loams and support forests with thick deposits of leaf and bark matter. The slopes are steep, the rainfall high and much more uniform throughout the year.
APS Victoria District Groups covering this region - Albury / Wodonga | Wangaratta | Strathbogie Ranges / Seymour / Euroa

Central Highlands

This region takes in much of the Great Dividing Range from the Grampians in the west to the high country around Mansfield. The Grampians is a sandstone region and soils around the perimeter slopes consist of loams, which will support a large range of native plants. Further east there is a wide range of rock outcrops from shales to granites and soils vary from clays to loams. Interspersed, and particularly to the north of the great divide, are the goldfield soils characterised by the box ironbark forests and clay loam soils, which have been so extensively dug over that much of the original loam soil has been replaced with clay loams mixed with quartz.

In the Kinglake, Gordon/Macedon areas, rich volcanic soils are encountered. The region has a wide variance in rainfall. The northern slopes are characterised by cold, wet winters and hot dry summers whereas the southern slopes have cold, wet winters but the summers are milder, due to westerly changes and some moisture.
APS Victoria District Groups covering this region - Strathbogie Ranges / Seymour / Euroa | Kilmore | Ballarat | Grampians / Pomonal

Western Plains

The volcanic plains of the western district consist mainly of heavy grey/black soils with volcanic rock outcrops. Combined with a higher and more regular rainfall they tend to be more friable at the surface, but crack extensively in summer.

Towards the South Australian border the soils are derived from marine deposits and are more sandy to clay loam formation.

Along the coast, coastal sand dunes have been formed and at Tower Hill the ash bed has broken down to very friable grey soils.
APS Victoria District Groups covering this region - Ballarat | Colac / Otway | Geelong | Hamilton | Warrnambool

The Otways and Strzelecki Ranges

Here sedimentary rocks have been uplifted and then eroded to form mountain ranges. The soils are generally friable loams to clay loams, rich in humus in forest areas.

The area experiences high rainfall and cold winters and plants need good drainage to do well in these conditions.
APS Victoria District Groups covering this region - Colac / Otway | South Gippsland / Leongatha | West Gippsland / Warragul

Eastern Ranges and Gippsland Lakes District

From Warragul to Mallacoota the ranges rise up to join the Alpine areas. The soils are mainly friable clay loams giving way to rocky shale outcrops near the snowline. Interspersed are some volcanic red/brown soils as found on the Errinundra Plateau. Most of this area is national park or forest reserve.

Along the river valleys, clay loams have been formed in the Latrobe and MacAlister river systems but near the coast and further east the river systems consist of more loamy soils.

Rainfall is high in the mountains north of Warragul but further east, rainfall declines to 700 mm and long periods without rain can be experienced.
APS Victoria District Groups covering this region - Bairnsdale | Latrobe Valley / Morwell | West Gippsland / Warragul

Melbourne / Geelong Region

Geelong

Coastal soils are mainly sandy loams but further inland soils become more clayey.
APS Victoria District Groups covering this region - Geelong

Around Melton and across to the You Yangs

Brown clay soils exist that are more friable at the surface. The rainfall is about 400-500 mm in this region due to the Brisbane Ranges uplift causing a rain shadow. The winters are cold and wet and the summers hot to mild with numerous cool changes.
APS Victoria District Groups covering this region - Melton & Bacchus Marsh

West of Darebin Creek to the mouth of the Yarra River

Heavy grey-brown volcanic soils exist. It is difficult to grow a wide variety of native plants in these soils.
APS Victoria District Groups covering this region - Keilor Plains / Airport West | Wyndham / Werribee

East of Darebin Creek and north of Burwood Highway

The Silurian-derived sedimentary soils have broken down into light grey loams over clay.
APS Victoria District Groups covering this region - Foothills Daytime / Blackburn | Maroondah / Blackburn | Yarra Yarra / Eltham

South of Burwood Highway

The tertiary sands have formed dark grey sand or loam over clays, characterising the former market garden belt.
APS Victoria District Groups covering this region - Wilson Park (Berwick) | South East Melbourne / Hughesdale | Waverley / Mt Waverley

The Dandenong Ranges and around Red Hill

Red-brown loams that are rich in nutrients and exposed to high rainfall. The foothills to these areas often have dark grey sands or loams over clay and can support a wide variety of plants, especially of the Heath type.
APS Victoria District Groups covering this region - Wilson Park (Berwick) | Foothills Daytime / Blackburn | Foothills / Boronia

"The Flora of Melbourne", produced by APS Maroondah, has excellent details on soil types and maps of soil deposits in the Melbourne area. It is recommended that you borrow a copy from your local Library.

If you are member of APS Victoria, purchase a copy from APS Vic book sales (go to Members Area) or check with your local District Group to see if they have a lending library with a copy.

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Tips for Growing Australian Plants

Most prefer well drained soils
Building up of garden beds, or provision of underground drainage, can be beneficial.

When adding soil, thoroughly mix it into the existing soil
Do not just spread soil on top of the garden.

Eliminate weeds from the planting area
Especially those spreading by underground runners.

Group together plants needing similar conditions

Plants needing full sun rarely survive in shady situations

Avoid over watering

Most grow well without extra fertiliser
High phosphate fertilisers may be harmful.

Use mulches and groundcover plants
They help reduce weed growth and keep the soil cool, moist and friable.

Lightly prune immediately after flowering
Light pruning promotes compact growth and more flowers. Heavy pruning kills plants which reshoot poorly from old wood.

Rejuvenating an old garden? >> Learn from Tony Cavanagh's experiences

Low water usage gardening >> How Jan Hall copes with unreliable rainfall and minimal water on tap

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Planting Times

The time to plant natives depends on your climate and the type of plant. Autumn is generally the best time, as it gives the plant time to establish itself before the next summer. Some areas of Victoria, however, are subject to frosts below 2 degrees C and cold conditions. In these areas it is best to plant in the spring after the cold has abated. Also, some native plants are hardy to cold weather and frosts and hence can be planted in the autumn after reasonable rains have occurred.

Recommended planting times

Northern Country, Wimmera and Mallee

Rainfall in these areas is below 500mm. Autumn planting is necessary as the effort to keep frequent moisture up to plants in the summer is time consuming.

Slopes of the Great Divide and adjacent ranges

Winter can be very cold and only the hardiest of new plants will survive. Here spring planting should be done as the summers are usually cooler and there is normally more moisture available over a larger part of the year.

Melbourne (most), Coastal areas, adjacent uplands, and East Gippsland

The climate is usually milder throughout the year and planting can be done from autumn through to the end of spring.

If in doubt as to when you should plant, consult your local APS District Group, native nursery, or look to when native plant sales are on in your area as this is a good indication of the best time to plant.

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Pruning

In natural conditions plants are constantly subject to pruning - animals eat the foliage and break branches as they trample through the bush. Unless the damage is severe the plants survive these set-backs and vigorous, healthy new growth follows.

Reasons for pruning

Appearance and flower production
Garden design, personal preferences and the function of a particular plant determine the type and degree of pruning for appearance each plant should be given. For example a screening plant might be regularly pruned to make it bushy, or a plant in a natural bushland setting might only be occasionally lightly pruned to blend in with the rest of the garden while maintaining a “natural” appearance.
Use these methods to achieve your desired appearance:

• Pruning for shape
  Heavy pruning is used to remove unwanted growth so a plant remains in proportion with the rest of the garden.
  Pruning to ground level is used on plants with a lignotuber, and suckering plants, to encourage the growth of multiple stems leading to a better shape, more foliage and more flowers.
  Lignotuber = a woody swelling at or below ground level containing buds from which new growth forms if the top of the plant is cut or burnt.
• Tip pruning - Carried out by pinching out the growing shoots forcing the plant to make new growth further back along the branch. This increases the number of flowers, makes the plant bushy and prevents it from becoming straggly.
  Tip pruning can be started when the plant is young.
• Flower picking - Picking flowers for indoor use and removal of old flowers immediately flowering finishes, stops the plant putting energy into seed production thereby increasing flower production next season.
• Regular light pruning - Used to promote and maintain dense growth of hedge and screening plants right down to ground level.

Maintenance of plant health
Remove diseased and damaged wood as soon as possible.
Clean out unwanted foliage in the centre of the plant to promote air movement and allow light to penetrate, thereby discouraging pests and disease.

Rejuvenation of old plants
Severe pruning rejuvenates and extends the life of many types of plants such as callistemons, grevilleas and others with a short life span.

Plants with a lignotuber should be pruned to near ground level just above the lignotuber.
Lignotuber = a woody swelling at or below ground level containing buds from which new growth forms if the top of the plant is cut or burnt.

Pruning rules

Keep pruning tools sharp and clean
Ensure your pruning tools are sharp, and kept clean by regular washing in disinfectant. Blunt, dirty tools damage plant tissue and introduce disease organisms.
Keep the cutting blades of secateurs and shears free of build-ups which might wedge between the blades springing them apart leading to bruising of plant tissue and ragged cuts.

Use the plant’s natural habit of growth as a guide to its pruning requirements
Plants which grow slowly should only require light pruning to keep them tidy and well shaped.
Fast growing plants may require frequent tip pruning and general pruning.

Prune shrubs back by about one third of the new growth and always ensure some green leaves remain
This rule applies except in extreme circumstances such as rejuvenating an old plant, or where specific knowledge of a particular plant’s response to pruning suggests a different approach.
Hard pruning into old wood may kill some plants or cause the loss of next season’s flower crop in species such as leptospermums, melaleucas and hakeas.

Pruning cuts
Make pruning cuts at an angle so water will run off and not collect in growing shoots where it will encourage fungal growth.
Undercut branches before making the top cut to remove them. This ensures a clean cut by preventing bark underneath the branch being torn from the plant or wood splintering as the branch falls away. If the branch is very heavy, cut it off a few centimetres further out from the trunk than your final cut so that most of the weight has been removed. Then make your final cut to remove the remaining short stub of the branch from the plant.
Disguise cuts by making them inside the plant’s foliage envelope so that the cuts are hidden by the remaining foliage.

Old and over-size plants
If a plant has got to the stage where you have nothing to lose, prune hard and see what happens.
Plants requiring constant heavy pruning to constrain their size are too big for the location. Consider replacing them with a smaller plant.

When to prune

WARNINGS
Never prune when there is the likelihood of damage to new shoots from extremely cold, hot or wet weather conditions.
Depending on your local climate and current weather patterns, late winter to early summer and late summer to early winter are generally the the best times to prune in Victoria.
Do not prune flowering plants while flower buds are forming (if flowers are desired next season.)

Established plants

Remove old dead flowers immediately after flowering.

General pruning as needed whenever weather conditions are suitable.

New plantings

Tip prune from an early stage if a bushy, compact plant is desired.

On planting, establish the future shape of the plant by removing unwanted branches.

Pruning notes for specific species of plants

These notes supplement the pruning rules and should be read in conjunction with them. They are based on the experience of people living in southern Victoria.

Acacia species
Trim to shape when planted. Thereafter remove dead wood, and, if required, straggly branches. If a bushy plant with heavier flowering is desired, prune immediately flowering has finished as far down the branch as the green wood or the last leaf buds nearest the trunk (typically about one third of the branch).

Alyogyne species
Pruning is desirable to prevent them becoming straggly.
A. hakeifolia - Straggly plants can be rejuvenated by cutting back to near ground level during spring. They will rapidly reshoot.

Anigozanthos species (Kangaroo Paws)
Should be cut back to 25mm above the ground after flowering.

Banksia species
Must not be pruned below the lowest green foliage as they will not reshoot from a leafless stem. For many species a savage pruning will rejuvenate them. Some species from fire-prone areas have a lignotuber and can be reinvigorated by pruning to near ground level above the lignotuber.

Brachyscome species
Brachyscomes are generally annual or perennial herbs bearing typical daisy-type flowers. Removal of spent flower heads often produces a new flush of blooms. They should be pruned and fed a little fertiliser when they have finished flowering or begin to look a bit untidy.
B. multifida - Wait until they start sending up new growth in early spring, then cut off the old growth.

Correa species
All species should be pruned immediately after the main flowering as soon as the new shoots come in spring, then regularly tip pruned to keep the flowers coming.

Callistemon species
Most callistemons can be heavily pruned after flowering. An exception is Callistemon viminalis and its cultivars, which have a weeping habit of growth and can be damaged by pruning. For all species remove the seed cases along the plant’s stems by pruning to promote more flower stems. Old plants can be rejuvenated by cutting them back almost to ground level as shown in the picture. (Photo - Tony Cavanagh)

Chorizema species
Tip prune lightly after flowering if desired.

Epacris species
Prune the shoots after flowering - erect types to within 2-3cm of the base, and pendulous types to half way along the new growth.

Eremophila species
Prune early in their life to make them bushy and then to prevent them becoming straggly.
E. glabra - Can be savagely pruned.

Eucalypt species
E. caesia - Can be coppiced and will reshoot from the lignotuber at the base of its trunk.
Eucalypts with blue-grey juvenile foliage - can be kept as bushy shrubs with juvenile foliage by cutting periodically to 20-30cm from the base.

Goodenia species
Respond well to cutting back to ground level.

Grevillea species
Cut on an angle just above a leaf node because this is where new growth shoots form. Rejuvenate straggly plants by cutting them back to near ground level during spring. Some cultivars such as G. ‘Robyn Gordon’ and G. ‘Superb’ respond well to this treatment.

>> Further information on pruning Grevilleas

Hakea species
Cut on an angle just above a leaf node as this is where new growth shoots form. Straggly plants can be cut back to near ground level during spring and will rapidly reshoot. Some species can be pruned down to bare wood.

Indigofera species
I. australis - Must either be lightly tip pruned after flowering or cut back to ground level and left to reshoot. Other types of pruning are not tolerated.

Melaleuca species
All respond well to pruning, and some species can be pruned down to bare wood.
Melaleuca ‘Green Globe’ - Can be heavily pruned almost back to bare wood.

Further information

>> Further information on pruning

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Plant Propagation

The average home gardener using simple tools and methods can have a lot of fun propagating plants. ANPSA, our national body has comprehensive information on how to propagate plants - just follow these links

>> Propagation from seed
>> Propagation from cuttings
>> Propagation by division
>> Propagation by grafting
>> Tricks of the trade
>> Further information

Precautions Against Frost Damage

Frost damages many plants and may even kill them, therefore steps to minimise damage need to be a consideration for every garden or plantation.

Most of Victoria is liable to frost at some time of the year. Areas along the Great Divide and the adjacent slopes are amongst the most frost-prone parts of Australia.

Local knowledge is important in planning for frost because features of the landscape such as valleys and hills can channel or divert cold air as it flows downhill, creating microclimates which are significantly more or less frost-prone than the surrounding region.
>> Further information about how to guard against frost.
Frost photograph courtesy of the Botanic Gardens Trust

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Australian Plants Suppliers

If you would like to advertise your nursery here, please >> email us or contact Mr Keith Buck on (03) 5998 7608.

Further Advice

1. Consult your local District Group.
2. Buy "Growing Australian" our resource kit for home gardens in Victoria. >> Buy on-line now
3. Visit APS Victoria's Open Forum. An answer to your query may already be posted there.
4. Check out these lists of recommended plants to suit various local conditions across Victoria
5. Visit a local garden featuring Australian plants and check out which grow well under your conditions
6. Consult ANPSA's Guide to Australian Plants
7. Consult "Gumnuts", ANPSA's native plant blog.
8. Read "Australian Plants Online", ANPSA's online native plants magazine.
9. Speak to knowledgeable local nursery people
10. Read plant books
11. Consult leaflets produced by government departments and local councils.