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SOIL |
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Checking out your Soil |
| Composting | |
| Mulch is a Must | |
| Using Water Wisely | |
| More Good Oil on Soil | |
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Wetters, Clay Breakers & Crystals |
Before going off to spend money at the nursery buying plants for your garden, you really must spend some time finding out what kind of soil you have. You are much better off planting plants that will do well in the conditions you have rather than trying to change the conditions to suit the plants you buy.
Soil Type
To check out the soil, you will need to dig several holes around the
garden. This will give you an idea of the soil profile - it may vary from place to place
in the garden. The holes you dig will have to be at least 30cm deep - more if you can. Pay
particular attention to the layers in the soil. A typical garden soil will have a thin
layer of top soil over a subsoil where there is not much organic matter. It may be heavy
clay, stony, rock, builder's rubble or the soil may be sandy to a great depth - typical in
beach-side gardens. All types of soil can support attractive garden plants, but if you try
to plant something that requires perfect drainage into a heavy, wet, clay soil for
example, you will have wasted your money, because it will almost certainly die.
Drainage
To check how well your soil drains, fill the holes with water and
check how long it takes for the holes to empty. If it drains away very quickly then you
probably have sandy soil and moisture retention will be an ongoing problem - mulching,
adding organic material and using water-storing crystals or granules are all strategies to
use. If the water is still there after a few hours then drainage will be a challenge in
your garden. 
Planting into raised beds, installing drainage, adding organic
material to attract earthworms that help to aerate the soil are all things to consider.
However the best option is to choose plants that do well in your type of soil.
Improving all soil types
Clay soil is hard to work with and doesn't drain well but it is usually high in nutrients. Sandy soils can be dug over easily but they often lack nutrients and dry out rapidly. The best way to improve any type of soil is to add large amounts or organic material. That is why it is so important to get those compost bins operational. In southern gardens and streets there are ample quantities of autumn leaves available for anyone with a rake and a packet of plastic bin liners - just keep filling them up. Be a brazen bag dag! If you have access to a mulcher, chop up the leaves (or run over them with the mower) so that they break down quicker. If you haven't, just add them to your garden or compost them. Because they don't smell you can easily compost them in a heap. Just keep turning them over regularly. By the next summer they will have been converted to lovely rich leaf mould.
Checking pH
Another easy and useful thing to do is to check the pH of your
soil. pH testing kits are available from large nurseries and they are dead easy to use.
There are different kinds but the most common involves getting a small soil sample (about
1 teaspoonful) and mixing it with a small amount of a chemical provided, then sprinkling
the mixture with the special powder provided. The powder will change colour and you then
match the colour of your sample with the colour on the card included in the kit. The card
will tell you what the colour means. If the pH is low (6 or below) then your soil is acid.
Plants such as azaleas, rhododendrons, camellias and many Australian plants will grow well in
soils with a pH of 4-6. If your pH is 6.5 - 7.5 then it is about right for most plants. If
it is 8 or above then it is alkaline. Plants such as lilac, bearded irises, lobelia and
figs will grow well in soils with a pH of 8-9. For most plants if the soil pH is too high
or too low, nutrients will be chemically "locked up" in the soil and they won't
be able to get the nutrients they need. Once again it is easier and more effective to
choose plants to match your soil than to try to change the soil's pH.
A soil PH test kit is available from the Global
Garden online shop.
Importing soil
Many developers' solution to a new development that has been cleared of all natural topsoil is to import some. However dumping topsoil onto existing soil with no attempt to mix the soil profiles together is bad gardening practice. Integrate the new soil with the site soil as much as possible and once again add organic material. This will encourage earthworms which are very good soil conditioners and work tirelessly on your behalf.
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One of the first tasks in establishing a garden is to begin composting. Not only is this an environmentally sound thing to do, but it will provide you with an ongoing supply of free, high quality, soil-enhancing material for the garden. Using compost reduces the need to use animal manures, which can often introduce all manner of weeds to the garden if they are used uncomposted.
You can choose to use a closed compost
bin which prevents rats and other nasties from breeding in the composting material and
literally puts a lid on the smell, or you can build an open heap. The disadvantage of a
bin is that it is much more difficult (but not impossible) to get air into the mix. A heap
is more untidy, but easier to manage and probably achieves a faster processing of the
materials. Your decision will probably be largely determined by the proximity of the
composting area to surrounding houses. Compost that is ready to be applied to the garden
(see right) does not smell bad, but has a sweet, earthy smell. Always use gardening gloves
when handling compost and other organic materials.
Tips on Composting
Locate your bin in a semi-shaded area of the garden. The material in the bin will get hot as it decomposes, but after the hot stage you want earthworms to colonise the compost. A bin in the sun may always be too hot for earthworms.
Use a variety of materials eg. food scraps, crushed eggshells, lawn clippings, leaves, soft prunings, animal manure, seaweed.
Don’t put weeds with seed heads and invasive plants that strike easily from stem tissue in the bin or heap. A really hot compost heap can kill these off, but you would need a very big heap and the outside of the heap would have to be turned to the inside in order to kill all the material.
Chop up everything as small as you can. Run the mower over leaves, put prunings through a mulcher or chop them manually. This greatly increase the rate of decomposition.
Keep the mixture moist - too wet and there will not be enough air, too dry and decomposition will slow down dramatically.
Get air into the mixture by turning it over regularly. Bins with ridges down the side and revolving bins are helpful in aerating compost. Without enough air the mix becomes anaerobic - it really stinks and can become so acidic that it can kill plants. A broomstick can be used effectively to fluff up material in a closed bin (even pushing the stick down into the compost to make "breathing holes" works well).
Decomposition relies on lots of microbes. The material you put in the compost bin will contain plenty, but to give the population a boost, add a shovelful of compost from the last batch, or a shovelful of soil. Packaged compost accelerators are of limited value.
Adding lime may reduce the smell and speed up decomposition but can cause a dramatic loss of nitrogen. Adding some gypsum will provide additional calcium and it also helps to reduce the smell.
Don't include meat and fats in your composting materials, and also avoid citrus skins and onions which earthworms hate. Earthworms are great for processing organic material into nutrient-rich worm casts, so locate your bin or heap on the ground, not on concrete.
It is a good idea to have two bins or heaps - one that you are adding to daily and one that is "cooking" - it takes several months for compost to be ready for use.
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Mulching is very important. To mulch means to cover the surface of the soil or growing medium with a layer of material eg straw, leaf litter or bark chips. Mulching is the solution to many of the problems that beset Australian gardeners, it makes gardening easier and, depending on the material used, it can also greatly enhance the visual appeal of a garden.
In our frequently hot, dry, infertile soils, mulching is a great problem-solver. These are some of the ways it can help your garden:
Mulches can be organic, inorganic or living. The choice depends on the nature of the garden, the purposes the mulch is to fulfil and the kinds of plants it surrounds. Because it adds nutrients, organic mulch is generally regarded as most desirable, however if long term weed suppression or a particular aesthetic effect is regarded as more important, inorganic or living mulches may be a better choice. Living mulch suppresses weeds and keep roots cool, but competes with other plants for water and nutrients. Often a combination is a good solution.
Types of mulches include:
Here are some tips to help you make the best decisions about mulch for your garden.
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Years ago the solution to the problem of the drought cycle was thought to be the building of more and bigger dams. This ancient country responded with disdain and revenge. Clearing and irrigation and the resultant rising water tables, turned great tracts of land into saline wastelands. The message became clear. The country would not be tamed by easy means. The only way was to learn to understand the nature of the land and the climate and to develop techniques that did not disturb its fine balance.
Most of us are urban dwellers, far-removed from this great struggle between man and the land. The one aspect we cannot escape, however, is the question of water usage. Our increasing consumption of water is one of the major environmental problems that will have to be tackled in the next decade. Part of the solution is in changing our habits and the perception of water as being free and unlimited. It is neither.
As responsible gardeners, what can we do? The following list is a good start.
1. Use a tap timer or a programmed watering system. Forgotten sprinklers waste an enormous amount of water.
2. Water less often but more deeply. Do not give the garden a light spray daily. It discourages the development of the deep roots that make your plants more robust.
3. Sprinklers lead to a great deal of water loss through evaporation. Instead use drip systems or surface or underground soaker hoses.
4. Choose drought-hardy plants. Australian native
plants, South African plants, Californian plants, Mediterranean plants, succulents and
cacti are among the most drought resistant plants available in nurseries. Group together
any plants that have greater watering needs so that additional watering may be confined to
the one spot and the water not wasted elsewhere.
5. Choose drought-resistant lawn grass (Tall Fescue in cool, temperate, semi-arid and Mediterranean climates, Couch hybrids in sub-tropical & tropical areas) . Don't cut lawns too short. If necessary, allow the lawn to dry off in summer. It will green up again quickly when it rains. Alternatively, avoid lawns altogether and grow trees, shrubs and ground-covers.
6. Mulch all garden beds thickly and add plenty of compost to the soil to allow the water to penetrate easily. If the soil is persistently water resistant ie if the water runs off and isn't absorbed into the soil, you could use a wetting agent.
7. Swimming pool covers dramatically reduce the amount of water loss through evaporation and mean that less "topping-up" is necessary.
8. While fountains may be appealing, be aware that 50% of the water in a fountain can be lost through evaporation on a hot day.
9. In urban areas, consider installing a rainwater tank to collect water for use on the garden.
10. Ensure that any leaking taps are fixed promptly. The water meter is ticking away with every drop, and the water conservation bomb is one that each one of us has to help to defuse!
Illustration:
Above right: Agave attenuata is a drought tolerant succulent
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Most Australians live in cities, which means that most Australian gardeners make their gardens in soil that has been compacted, de-oxygenated and nutrient-depleted by decades of human traffic. Unless we deal with these problems in our soil, then the plants we buy are going to find it very hard to survive.
Compaction
It is not difficult to diagnose compaction in the soil. When you go to push your
trowel into the soil and it springs back at you, it's pretty clear that the soil
is compacted. Compaction matters for a number of reasons. Firstly plants rely on
their roots to take up all the water they need. If the soil is hard and
compacted, then the roots find it difficult to push their way through. This
means the plant will not be anchored well either, so can be easily blown over in
strong wind.
Oxygen needs
The most important problem with compacted soils is that the compaction prevents
plant roots from having access to the oxygen that is vital for respiration i.e.
creating the energy for growth. A good soil has plenty of air spaces or pores in
its structure. When it rains, or when the plant is watered, the oxygen in the
pores is dissolved in the water and is taken up by the plant roots. If the
texture of the soil is very fine e.g. a clay, or the pores have been squashed
flat by pressure from above from foot or vehicular traffic, then there will be
insufficient oxygen in the soil. Also the water won't drain away and stays in
the pores, preventing oxygen from entering.
Dealing with deoxygenation
Fortunately there are plants that are tolerant of compacted soils and this is
the easiest way of dealing with the problem. Alternatively you can cultivate the
soil by ripping or using a chisel plough for large areas, or a fork for small
areas. You can also add material to improve the porosity of the soil. Organic
material is the best material to add. It also attracts earthworms which help to
aerate the soil. Gypsum can help, but only in soils which have a weak structure.
Growing a crop of potatoes is also a good way of loosening up compacted soils.
Nutrients
Urban soils are often lacking in nutrients, especially where organic
material such as leaves and grass clippings have been been constantly removed
and not allowed to return nutrients to the soil. Adding compost, leaf mould,
animal manures, seaweed, straw, etc. on a regular basis is the best recipe for
plant health. A word of 
warning though, don't incorporate organic matter deeper
than 20cm - it can produce gases around the roots of plants and kill them.
Organic mulches are great for water conservation and weed control as well.
Organic material does however use up nitrogen as it breaks down. A good way of
replacing nitrogen is planting a green manure crop of legumes e.g. peas (see
right), lupins
or beans and digging the crop into the soil. Chemical fertilisers allow you to
be more scientific and exact in the way you apply nutrients.
Soil pH
Plants use the chemicals in the nutrients for reactions within their
tissues that produce the huge range of substances that make up the plant world.
Sometimes the uptake of these chemicals is hampered by the chemicals makeup of
the soil e.g. if the soil is too acid or too alkaline, most plants will have
difficulty accessing the nutrients, even if there are plenty of them in the
soil. A pH test will tell you if your soil is very alkaline or very acid.
Luckily there are plants that can tolerate either highly acid or highly alkaline
soil, and these are the plants you should use if this is a problem in your
garden.
Applying fertiliser
Over-fertilising can cause problems for plants. Don't add more than the
recommended application, or apply it more frequently. Never apply liquid
fertiliser to dry plants. Too much fertiliser in the soil makes it hard for
plants to absorb water and roots may even lose water if the soil is
over-fertilised. Don't kill your plants with kindness.
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Soil Wetters, Clay Breakers & Water-saving Crystals
All of these products can be useful in our dry climate.
Soil
wetters eg Saturaid, EcoWet, Wettasoil & Ezi-Wet overcome the problem of
water-repellent soils. They break down the surface tension of the water and
allow it to enter the soil. Use a soil wetter if the water just runs off when
you hose the garden or you find that the soil is still dry a few millimetres
under the surface even after you've watered. Use it also to rewet potting mix
that has dried out and use it on hanging baskets that often become too dry and
water-repellent.
Clay-breakers are chemicals that actually change the structure of the soil. They change the molecular structure so that soil particles will clump together and open up spaces between them so that water and nutrients can flow through and air can enter. Clay soils often have a poor structure. They are often compacted and there is very little in the way of pore space. This means that it is hard for plant roots to push through the soil and they also cannot get the water, food and oxygen they need to grow properly. Digging up the soil, adding gypsum or organic matter and encouraging earthworms may all help to improve the structure of the soil, but where this is not possible, a clay-breaking product is a useful option. Products include GroundBreaker, Clay Breaker & Claygon among others.
Water-saving crystals or granules are water absorbing polymers. They are incorporated into the soil and swell up with water to form a gel when it rains or when the soil is watered. Plants can then access this water as needed. (There is some debate how readily plants can actually do this however.) These crystals or granules can be dug into soil or mixed in with potting mix. (They are included in some of the more expensive potting mixes.) Don't be surprised after heavy rain to find clear gel oozing up from the ground somewhere where you've emptied out some old potting mix! It will be the water saving granules doing their thing. Products include RainSaver Water Crystals.
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