Australian Plants for Adelaide Gardens

The following is a transcript of the opening sections of a booklet published by the society in 1990. It was prepared by the late Ivan Holliday and others named in the Preface based on experience gained by our members.

In the printed book, this section is followed by three more covering Coastal and Near-Coastal, Adelaide Plains, and Mt Lofty Ranges regions, and for each region has lists of suggested plants under the groupings Ground Cover, Other Small Plants, Climbers, Shrubs, Trees and Ferns.

Current society members are in the process of revising the lists so that they can be published electronically.

Preface #

This publication is a completely revised edition of the original publication (and its revised edition) which was compiled in three sections “Coastal and Near-Coastal Gardens” by John Scarvelis; “Adelaide Plains” by Robert Smith; and “Mount Lofty Ranges” by Laurie Russell.

Although such a publication as this cannot hope to cover the entire vast range of Australian native plants which may be grown in the Adelaide area, this revised edition is much more comprehensive than its predecessors, and should fill an important need for gardeners in Adelaide. It should always be remembered that most of the textbooks available are written by authors from the Eastern States, where climate and more importantly, soils differ markedly from those in Adelaide and to an extent which may cause some of the textbook information to be misleading to the people of Adelaide.

In compiling this new edition, which retains the format of the previous editions, I was assisted by Neil Shirley of the Fern Society of S.A., who prepared the information on Ferns. Neil’s contribution is gratefully acknowledged.

It is hoped that this publication will encourage and help the people of Adelaide to protect and enhance the character and beauty of their environment and to learn a little more about one aspect of this country’s heritage – it’s native plants, by growing and protecting them.

Ivan Holliday, Past President S.G.A.P. (S.A. Region) (November, 1990)

Introduction #

This book has been prepared as a general guide to the people of Adelaide and environs in their use and selection of Australian native plants. Naturally, in such an area there is considerable variation from garden to garden and it is not always possible to be precise when advising growers on their chances of success with a particular species. As a consequence the publication centres mainly on those species which have proved to be generally reliable over time under a wide range of Adelaide soils and conditions, but presents a different list for areas such as the coast or the Mount Lofty Ranges where soils and / or climate affects the range of suitable plants.

Even so, there are many more species (some not yet tried) which may well be successful in your garden and growers should not be discouraged from trying a species which does not appear on the lists.

Planning the Garden #

When planning your garden observe the natural landscape around your property, the landform, soil and rocks, the animals and vegetation, and then try and fit your plan into this environment with minimum disturbance.

Designs evolved around existing contours and taking advantage of local materials such as stone and native vegetation are more likely to be in harmony with the surrounding landscape.This point is particularly relevant to gardens in the Mount Lofty Ranges where in places, increasing human impact is causing environmental decay.

If your property is in the Ranges, try and play your part in preserving this beautiful area of our State. Unless the people who live there want the character and beauty of the Ranges to be retained and enhanced by saving and recreating areas of natural vegetation, then the Ranges are going to regress still further.

A collection of beautiful plants does not necessarily make a beautiful garden. Plants should be chosen to relate to each other and to the area for which they are intended, giving shape, form and harmony to the total space. For example, broad- leaved tropical species such as the Queensland Umbrella Tree (Schefflera actinophylla) would look out of place among a massed planting of fine-leaved, dry area species, not to mention the quite different watering demands.

In this regard, species of reasonably similar watering, nutrient and climatic requirements should be located together because they usually relate visually as well as functionally – and don’t be afraid to use a massed planting of the one species, which can often be more rewarding than a mixture.

If you prefer a mixed garden with some natives and some exotic plants, be very careful in your siting. Many natives (but not all), particularly in the heavy soils, grow too lush if over-watered, resulting in weak plants prone to disease and wind damage. Some of the hard-wooded myrtaceous species such as most Callistemon and some Melaleuca, are so hardy that they thrive with, or without extra watering. Hence such species are ideal for providing an informal living edge to a lawn, especially if the lower growing bushy types are chosen.

Above all, a garden is a place to be used and enjoyed. So in designing your garden, consider how it will best suit your needs. How a mound or a dense shrubbery can be used to soften a hard line or create a pleasant private enclosure, perhaps a secluded play area for children; how a pathway can be used to disappear through dense shrubbery as an element of surprise and interest, or surface run-off used to create a hollow as a natural drainage area where special water loving plants can be grown. A good garden, like a well designed house, is more successful when it performs its intended functions.

Site Preparation #

Plants grow best when free from competition. Thus efforts should be made to eradicate weeds before planting, which is easier than afterwards.

Use of a non residual weedicide such as Round-Up may be the best method of clearing the site of the existing weeds.

In open areas a deep cultivation before planting will assist in plant growth. This is particularly worthwhile if planning a wooded area where the tree and shrubs can all be planted at the same time. This treatment also helps retain moisture.

If planting new plants into a well-grown garden, clear around the immediate area and dig deeply to temporarily remove root competition and give the new plant a good start.

When preparing the planting hole where limestone is present ensure that the limestone is broken up using a crowbar to allow for root penetration. Similarly for heavy clay soils break up the soil to a depth of at least 400mm and thoroughly mix with 50% coarse sand to a depth of 300mm. Do not fill plant holes in heavy clay with free draining friable soil as the surrounding clay will retain moisture and drown the plant. It is better to mix a coarse sand with the clay in which the plant is to be planted in a much larger and deeper hole to assist clay breakdown and drainage.

As there are a wide range of native plants tolerant to many different soils, it is suggested, however, that in most instances, the new gardener does not change the soil condition.

When to Plant #

Provided water is available, successful planting can be undertaken at almost any time of the year, although weather extremes such as summer heat-waves and very cold, wet spells in winter, are best avoided.

For the beginner the safest time to plant is in the autumn when the soil is still warm from summer heat, promoting strong root growth before the onset of winter. Autumn planting produces well established plants with less follow-up watering. For quicker growth, however, spring and summer planting is best, provided the plants can be artificially watered.

Where frosts, long cold periods or water logging are a problem, however, it is best to plant in late spring, so that the plant can become well established before meeting these conditions in the ensuing year.

Late spring-early summer is also the best time to plant species from the warmer, sub-tropical areas of Australia, such as the rainforest trees of the East Coast, some of which do well in Adelaide.

How to Plant #

This may vary slightly according to soil conditions and topography. Normally, a hole should be prepared which is only slightly larger than the container in which the plant is growing and ideally the soil should be moistened.

It is important to plant with a minimum of root disturbance. Ensure that the potted soil is thoroughly moist before removing the plant from the container. Most plants can be gently removed from a tapered container by placing a hand over the top surface with the plant stem between the second and third fingers – turn upside-down and tap the pot edge on a solid object to free the plant.

With straight-sided tubes and plastic bags the plant can usually be removed in similar fashion to the above, although a firm squeeze around the middle circumference of the container prior to turning upside-down will usually free the more difficult ones. Plastic bags need to be gently shaken, not tapped. In very difficult instances where the plants refuse to budge, one side of the container can be carefully slit with a razor blade or sharp knife and the container taken from the soil.

If the plant is pot bound, the roots should be carefully loosened and the most twisted ones cut off before planting.

Place the plant in the prepared hole so that the top of the soil in which it is growing corresponds with the soil at ground level. After planting, carefully firm the soil around the plant, water thoroughly and fill in any soil subsidence which occurs.

A shallow saucer about 500mm to 600mm diameter can be provided around each plant to hold water (except where drainage is poor) and this can be filled with mulch which will conserve moisture and insulate the root system from temperature extremes. The mulch should be kept away from the plant trunk to reduce the danger of collar rot.

At the time of planting a handful of organic fertiliser such as “Blood and Bone” can be beneficial in some soils if placed a few centimetres below the root zone of the young plant and covered with soil so that the roots do not contact the fertiliser initially.

In some areas it may be necessary to protect the plant from wind damage, frost or animals for the first few years. Hessian tied to four stakes 500-600mm apart will provide for this. Do not use sheet metal because it radiates too much heat in summer and is not enough insulation against frost.

Stakes should only be used if the plant needs support – and then do not let them remain too long or the plant will become dependent on them.

If staking is considered necessary always use two or more stakes with the ties lightly tensioned to avoid bruising but allowing for natural flexing of the tree so it can develop its own strength. Pieces of garden hose or pantyhose around the point of restraint are ideal.

Low growing, spreading plants can be tripod staked with the tree prunings angled through the foliage.

Soils #

As a very general guide to the grower the soil map* has been included which categorises the Adelaide soils into broad types. Adelaide soils, however, are quite complex and variable and in many places, have been altered by their use as gardens over time, so the new gardener is best advised to have the soil tested before drawing any firm conclusions.

Good drainage too, plays an important part in successful growing of many native plants. Hence, limestone soils on steeper slopes (e.g. the Glen Osmond-Beaumont area) may grow some plants successfully which fail on poorer drained similar soils on the flatter plains.

Most of the Adelaide Plain’s soils are of clay-limestone origin, usually neutral to alkaline in the topsoil but alkalinity increasing with depth. Some of the foothills soils in suburbs such as Tea Tree Gully, Athelstone and Hope Valley, are lime-free sands which are more conducive to growing many of the more difficult native plants. Deep dunal sands occur along the coast, mainly very alkaline and containing some salt. Here plants are usually subjected to strong salt-laden winds which play an important part in determining which ones may succeed.

The Mount Lofty Ranges are quite extensive and the map does not attempt to show the soil variations of this complex region. Nonetheless, two soil types are common – podzols of acid reaction and skeletal soils – rocky soils with little topsoil or nutrient. The cooler, wetter climate may often play a more important role than soil type when choosing plants suitable for growing in Hills gardens.

*Reproduced from ‘Growing Australian Plants’, Holliday, Ivan and Lothian, Noel Rigby, Adelaide; revised ed. 1981. For further reading on Adelaide soils refer Chapter 1, pages 9-13 of ‘Growing Australian Plants’.

After Care #

Watering #

There are too many variables such as weather conditions, microclimates, soil, density of planting, the plant itself – its capacity to withstand dry spells to lay down specific guidelines for watering.

Deep soaking by slow irrigation to encourage deep root systems is the recommended method of watering native plants. Frequent light wanderings from a sprinkler or hand-held hose should be avoided as it encourages surface rooting.

A way of reducing water costs is to select species capable of surviving on natural rainfall, once the plant is established. Species native to the area or species from a similar climate and soil type are usually the best choices to meet this requirement.

Mulching #

A good method of conserving moisture in the soil is to mulch. Many mulch materials are used, the organic mulches such as pine or casuarina needles and chip litter being the most sympathetic visually.

Advantages of mulching include:

• leaves and sticks dropping from trees become part of the mulch,
• as the mulch decomposes it forms a leaf mould material similar to the natural floor of a forest,
• ground cover plants thrive in them,
• hand weeding is very easy in a friable material of this kind.

Disadvantages are:

• mulches tend to keep moisture out as well as in, so that rain in summer may not penetrate into the soil below,
• they use up available nitrogen when decomposing. This can be overcome by the careful use of a slow release nitrogenous fertiliser,
• some materials such as pine bark and needles (unless very old) contain toxic leachates. These disadvantages are rarely serious if the mulch is laid fairly thinly (5-6cm) and gradually built up as the lower layer decomposes.

Weeding #

Weeds competing for moisture and nutrients often look out of place among natives and should be removed.

The most effective and safest method of removing weeds is by hand pulling. Mulches greatly assist by repressing weed growth and enabling easy removal by hand.

Digging around plants can damage the root systems of native plants and in some cases, be fatal. Cultivation also tends to spread weeds, particularly those of a bulbous nature.

Chemical herbicides can be effective if particular care is taken and they are used at recommended strengths. They are best used to remove troublesome weeds prior to planting out the area with desired plants.

Fertilising #

Small amounts of fertiliser applied over the root zone after it has been watered, can benefit many native plants. Caution is necessary, however, as many complete fertilisers which contain phosphates can be fatal to some natives, particularly proteaceous plants such as banksias.

Used in moderation Blood and Bone is one of the safest fertilisers. It is particularly effective on eucalypts and has the added advantage that it will deter rabbits if applied in a ring around the plant. Jomoco is a good organic fertiliser to give plants a boost.

Slow release fertilisers are a good method of fertilising in conjunction with drip irrigation.

There are no hard and fast rules, especially as soils are so variable.

The grower is best advised to experiment with fertilisers only if a plant is ailing or appears to need a boost.

Pruning #

Pruning should be carried out mainly to shape and strengthen plants to meet desired requirements. With care and subtle pruning at regular intervals this can be achieved without desecration.

If the size of a shrubby plant is required to be limited, frequent light pruning is better than spasmodic heavy pruning. This method retains the natural appearance of the shrub without exposing woody branches which may encourage disease.

Most native plants are best trimmed immediately after flowering, removing the dead flowers and ensuring that the plant does not become dominated by seed capsules. Such a method is particularly successful with many of the hard-wooded myrtaceous plants such as Callistemon, Melaleuca and Leptospermum, because it encourages soft new growth followed by a wealth of flowers each year.