Aquaponics combines hydroponic food production with fish aquaculture to create amazingly productive food and fish growing systems. In an ironic twist, water restrictions placed on backyard gardeners have provided a much needed boost for this fledgling aquaculture-based food production system.

Maintaining traditional home vegetable gardens during the drought has been impossible without a good supply of tank water. Water restrictions do not apply to aquariums, so aquaponic growers have been able to continue to produce a bumper harvest regardless of the rainfall pattern. Fortunately, aquaponic systems are very economical water users.

Water enriched by fish waste is pumped through gravel beds or floating rafts of vegetables and other food plants. Plant roots extract nutrients from the water and use it as a food source. The clean water trickles (usually by gravity) back to the fish tanks below. Covering the fish ponds reduces evaporation, so the only water lost from the system is that which is actually used to grow plants. Pumps (electric or solar with battery backup) are required to move water from the fish tank to the grow beds and to oxygenate the water and keep the fish alive.

Many home owners will be attracted to the thought of an endless supply of backyard barramundi, silver perch, trout or jade perch that an aquaponic system can provide. But if you do not think you could bring yourself to harvest and eat fish you have seen grow to maturity, there is always the gold fish option. While leafy green are an obvious aquaponics crop, your potential harvest appears only limited by imagination. Enthusiasts have demonstrated that tomatoes, capsicum, onions, peas, beans, parsley, strawberries, sweet corn, broccoli and even pawpaws can be successfully grown using aquaponics.

Earth Garden, arguably Australia’s best known magazine on sustainable living and organic gardening, has caught the aquaponics bug. Their latest offering is titled, Easy Aquaponics – Backyard Fish and Food and can be purchased on-line through their Good Life Book Club ($19.95 plus postage -www.earthgarden.com.au). This 78 page magazine style publication profiles a number of inexpensive, do-it-yourself systems. The owners of each system explain how they got started, mistakes made, and various modifications. It is all good, practical advice from people who have learnt what works best through their own trial and error process.

Queensland based aquaponics enthusiast, Murray Hallam, provides a comprehensive introduction in his 90 minute DVD, Aquaponics Made Easy! ($33 plus postage - www.aquaponics.net.au). The program guides you through the basic principles behind aquaponics, provides a detailed analysis of each of the components in a small scale commercial system, demonstrates techniques for testing and maintaining water quality and discusses suitable plant and fish species combinations. For those serious about sustainability and the economics of this system, he examines use of solar power and details methods of reducing input costs by growing your own fish food.  The site also provides information on small scale, of-the-shelf aquaponics kits specifically designed for backyard and balcony food and fish culture.

Western Australia gardeners have been quick to adopt aquaponics and the state is at the forefront of the aquaponics movement. You can tap into this experience via Backyard Aquaponics [www.backyardaquaponics.com.au].

Gardeners are reporting increased incidence of a little known citrus pest. Close inspection and timely intervention may be the key to controlling the citrus blossom midge.

Citrus trees that fail to carry fruit to maturity are a common source of frustration for gardeners. Young trees often flower prolifically, but fail to form fruit or drop the fruit when it reaches the size of a pea. These trees may simply be too young to carry fruit to maturity. This fruit shedding is a natural response that allows the tree to put all its energy into leaf growth. The problem usually rectifies itself in a year or two when the tree matures.

A second common cause of fruit drop is a nutrient imbalance. Use of compost, balanced fertiliser containing nitrogen, phosphorous and potassium, calcium (in the form of gypsum) and trace elements are vitally important. They ensure that the tree can set and sustain fruit development through until harvest. Adequate water is necessary to allow for the uptake of nutrients, so regular watering and mulching are also essential.

A number of gardeners have recently alerted me to the fact that mature, well nurtured and regularly watered trees have flowered prolifically, but failed to form fruit. Investigation under a microscope has revealed infestations of the little known citrus blossom midge.

This tiny fly produces maggot-like larvae that infest citrus blooms. The lifecycle is very rapid and many generations of midge flies can be produced in one flowering season. Lemons appear particularly susceptible, although gardeners are also reporting attack on mandarin trees. Unseasonally warm, dry weather may be responsible for increased incidence of this pest.

Systemic chemical controls used by citrus producers to keep other pests in check also control citrus blossom midge, so this pest is not commercially significant. Most home gardeners rarely spray their fruit, so infestations appear more problematic in back yard trees.

Examine your citrus blooms closely this weekend and look for evidence of tiny maggot-like larvae. Look for unusually large flower buds within a flower cluster as this tends to be a characteristics of infested blooms. Remove and dispose of any buds infested with larvae. Applying pyrethrum sprays just before dark to flowers of infested trees may help to minimise damage caused by the citrus blossom midge and help to boost your potential harvest.

Is there a risk of cadmium accumulating in potatoes grown in tyres? To answer this question, it is necessary to look at the much broader issue of cadmium contamination in soil and food crops.

Cadmium enters the environment as by-product of mining and smelting of zinc, lead and copper and metal reprocessing. Burning of domestic, hospital and industrial waste, fossil fuels and exposure to tobacco smoke are also significant sources. Cadmium is used to make batteries, metal plating, alloys for soldering, brazing and electrical contacts, pigments, rubber (including tyres), paint, ink, stabilisers used in plastics and cement. Unlined galvanised tanks also contain impurities of cadmium.

Impurities in commercial fertiliser, particularly those found in superphosphate are a significant source of cadmium in soil and crops. Fertilised soils in Australia contain 2-6 times the level of cadmium when compared with unfertilised soils due to the use of superphosphate. Organic certification requires the use of naturally low-cadmium phosphate rock. There is currently no viable process for removing cadmium contamination. Cadmium is a cumulative toxin that concentrates in the liver and kidneys. The National Occupational Health and Safety Commission (NOHSC) classifies cadmium as a probable human carcinogen.  While acknowledging that workplace exposure to cadmium should be minimised, the NOHSC identifies dietary intake as the main source of exposure for most people.

Fertiliser manufactured in NSW and Victoria and those sold or manufactured in South Australia must carry a warning statement if concentrations of cadmium higher than 1mg per kg.  Absence of such a warning is not a guarantee of low cadmium levels. No such regulations apply to fertilisers manufactured and sold in other parts of Australia or those manufactured interstate and overseas then sold in NSW and Victorian.

While cadmium is generally found in insoluble forms in the soil, soil acidity, salinity and the type of plants being grown affect uptake. Potatoes are known to accumulate cadmium. This is of particular concern because potatoes form a significant part of most people’s diet. Cabbages, carrots, radishes, lettuce, turnips, tobacco, cocoa, chocolate (especially dark chocolate) and peanuts also accumulate cadmium. Significant levels are also found in offal (especially from sheep), shellfish and crabs. Peanuts imported from China that typically find their way into ‘no-name’ brands commonly fail quarantine tests for acceptable cadmium levels.

Finally to the issue of growing potatoes in tyres. I have been unable to find anyone prepared to put their name to a scientific research paper that provides definitive evidence that cadmium leaches from tyres into the soil. However, given our knowledge of the various ways that cadmium finds its way into the environment, it seems most likely that this is a reality. Given that we know certain edible plants, including potatoes are known accumulators of cadmium, I can only agree with your conclusion that no edible crops should be grown in tyres. In fact, I do not advocate using them at all in the garden.

What is crop rotation and why is it important?

If you grow the same vegetables or their close relatives in the same soil season after season, two things can happen. Firstly you run the risk of depleting the specific nutrients required in the greatest quantities by related crops. For example, all Brassica crops are very hungry nitrogen feeders, so it is common for them to be planted in a bed that has previously been planted with a nitrogen enriching, green manure crop. Secondly, you are likely to experience an increase in the specific pest and disease problems commonly associated with that group of plants. For example, while all members of the family Solanaceae are very prone to attack by soil nematodes, many other crops do not support nematode populations. By rotating crops from one bed to another, you avoid a continuous build up of nematodes in any one bed. Vegetable crops should be rotated according to family groupings. Some examples of the main family groups are listed below:

Solanaceae – capsicum, chilli, eggplant, potato, tomato
Brassicaceae – broccoli, Brussels sprouts, cabbage, cauliflower, kohlrabi, radish, rocket, swede, turnip
Curcurbitaceae – cucumber, melon, pumpkin, rockmelon, squash, watermelon, zucchini
Fabaceae – all legume crops such as peas and beans
Amaryllidaceae – garlic, leeks, onions
Apiaceae – carrot, celery, parsnip
Asteraceae - chicory, endive, lettuce

Where Winters are Warm
The tables below are based on two major rotations per year namely Winter planting (April – September) and Summer planting (October – March). This timetable allows for progressive planting and harvesting as well as allowing time for crops to mature for seed saving purposes.  A six bed rotation is ideal for warm climates as it leaves room for a dedicated green manure bed as well as individual beds for peas/beans and brassica crops. Where space is limited this can be reduced to five beds by combining Apiaceae and Asteraceae crops in the one bed. Gardeners in tropical areas have difficulty growing vegetable crops during the summer ‘wet season’. The summer rotation outlined below can be used as a winter ‘dry season’ planting guide in the tropics.

Example of winter layout in warm climates

In this example, the Solanaceous crops grown in bed six during winter move to bed one during summer. Beans grown in bed one during winter, join corn in bed two, bed two moves to bed three and so on. Some crops not suitable for summer planting like brassicas are replaced with more climatically suitable curcurbit species like cucumber, pumpkin and zucchini.

Where Winters are Cool
The tables below are based on two major rotations per year namely Winter planting (March – October) and Summer planting (November – February).  Gardeners in cool climates often start off their summer vegetables in seed trays or pots, planting them at an advanced stage as soon as continuously warm weather can be guaranteed.

This timetable allows for progressive planting and harvesting as well as allowing time for crops to mature for seed saving purposes.

This sample four bed rotation system includes a winter green manure crop. Solanaceous crops replace Brassica crops during summer. Bed two moves to bed three and now includes corn and cucurbits. Bed three to bed four and bed four becomes bed one.

When laying out formal vegetable gardens be sure to leave adequate space between beds. Pathways should be at least wide enough to freely move a wheelbarrow. To contain soil and compost within beds and define pathways, untreated timber, rocks, bricks or other available materials may be used to surround vegetable gardens. Sawdust, decomposed granite or other materials may be used as pathways or living paths of groundcover plants including clover and pintos peanut may be grown in between beds.

Can vinegar be used to control weeds?

Vinegar is made from acetic acid. Acetic acid is registered for use as a non-selective herbicide in several countries overseas, but I am unaware of any such registrations in Australia or New Zealand.

The concentration of acetic acid in household vinegar is typically not more than 5%.  While household vinegar directly applied to plants will kill some weeds, it is not terribly effective at this strength. You could experiment yourself to see if direct application of vinegar works on problem weeds in your garden.

Formulations used as herbicides typically have acetic acid concentrations of 10-20%.  While using these products poses no long term environmental threat, it should be noted that concentrated solutions can burn the skin if mishandled.

The acid breaks down plant cell membranes exposing the contents of the cell to desiccation. Acetic acid is not translocated through the plant so will not work its way down to the root system of aggressive weeds with underground tubers or rhizomes.

Tips for Growing Instant Plants
We live in a world of instant gratification. Many people don’t want to wait for plants to grow from seeds or cuttings. Purchasing all your plant needs from the local nursery can be an expensive exercise, especially for those just starting out. Gardeners are a generous lot and have traditionally swapped plant material. You do not even have to be particularly adept at growing plants because some species grow well despite you. Throw out the rule book. Many plants can be grown from metre long cuttings, cut up with a carving knife or literally ripped apart. Be prepared to be shocked at how easy it is to propagate some of our most popular garden plants.

Grow these plants from metre long cuttings

Quick Tips

• Look for sound sections of stem.

• Cut longer stem sections into pieces.

• Remove excess foliage – it will fall off anyway.

• It is OK to cut individual leaves in half.

• Use a flat cut on the bottom of the cutting and a slanted cut on the top of the stem – you will always know which way is up when it comes time to plant.

• Insert 30cm of stem into the ground to ensure the cutting stays upright.

Take to these plants with a carving knife

• When dividing grass-like plants, just imagine you are parting hair!
• Be brutal and use a sharp knife to cut cleaning through the plant - roots & all
• Avoid being greedy – don’t cut individual sections up into tiny pieces

Really rip into these plants

Hippeastrum
Autumn Crocus
Other bulb forming plants

Quick Tips

• Avoid cutting into onion-like bulbs or they will tend to rot.
• Separation carried out during late autumn is less likely to disrupt flowering.
• Plant back at their original depth – hippeastrums like their necks exposed.

Many gardeners suspect that water restrictions are here to stay no matter what the weather does. While much of the focus of waterwise gardening education has revolved around plant selection, gardening in dry times is as much about how you garden as it is what you plant. In response to the restrictions, some home owners have embarked on their own backyard blitz, filling gardens with natives, succulents and grasses in the mistaken belief that banishing exotic flowers and foliage will save water. Look around and you will notice that deep rooted trees and well-established shrubs have faired remarkably well despite the water restrictions.

• The Most Efficient Way to Store Water Is In The Soil

Avoid water leaving your property
Your property is a huge catchment area. Take advantage of this by directing runoff from driveways and paving on to lawns and gardens. Use porous materials like gravel on walkways so that water can soak in and become available to trees and shrubs. Incorporate mulch filled swales into larger garden beds and on sloping land. They will serve as infiltration pits when heavy rain falls.
Recycling organic waste so that the soil holds moisture
There are some good commercially available compost products available from your local nursery. Unfortunately, most have been pulverised, deodorised and pasteurised. They contain nutrients and are a source of organic matter, but much of the life we hope they will inject into our soil has generally been processed out of them. There is really no substitute for home made compost. Resolve to recycle all garden clippings and kitchen waste back into the garden. Compost bulk garden waste in a heap. Buy a bin or bury kitchen scraps. Work your way around the garden digging holes 30cm deep between existing trees and shrubs and bury kitchen scraps each day. Other strategies for improving the moisture holding capacity of soil include incorporating coir peat into the soil. Avoid gimmicky, synthetic products. Read the label, if you need to wear gloves and a mask to use it don’t bother. It cannot be good for the soil.
Use seaweed and other wetting agents
Always water new plants in with liquid seaweed. It stimulates soil organisms like fungi and bacteria, which in turn help release nutrients to plant roots. Seaweed increases the disease resistance and drought tolerance of plants by thickening cell walls. Seaweed is also a wetting agent. In other words, it helps the soil to absorb and retain moisture – but keep in mind that it takes time to work. For more instant results try one of the commercially available products available. Organic Crop Protectants has a product called Eco-Hydrate that actually helps soil absorb moisture from the atmosphere (dew and humidity).

• Rainwater Tanks And Grey Water Can Sustain Your Water Needs

Install A Tank
Take advantage of the government rebate to install a rainwater tank. At least then you can water the garden when you want and how you want. But remember, unless you intend to install an inline pump or a tank stand, the water will only really be of use if you can store it at the highest point in the landscape and use gravity to create pressure. A five thousand litre (1100 gallons) water tank will be empty in under 3 hours at normal household flow so think big and install the largest tank you can afford and can accommodate. Drip irrigation is still the most efficient way to water your garden, so consider connecting the tank to a pump and drip irrigation system. Install a programmable timer and you can basically forget about water all together.
Recycle Grey Water
The water that currently goes down the drain from your laundry, kitchen and bathroom equates to the average household outdoor use. Simple diversion values available from hardware companies and mail order suppliers like Green Harvest allow water to be temporarily diverted for garden use. Just remember that diversion valves work on gravity. The pump in your washing machine is a volume pump not a pressure pump. If you add an additional length of hose and expect your washing machine to pump the water out onto the garden you will burn out the pump in your washing machine. You also need to be careful what you put down the sink, especially in the laundry. Use only no phosphorous and low sodium laundry products (ref. Lanfax Laboratories) such as:

Overcome potential problems of salinity by avoiding the use of water softeners when washing clothes. A little vinegar in the final rinse has a similar effect. The vinegar will not be detrimental if the water is put on the garden as it will simply counter-act the alkalinity associated with the powder or liquid products used to wash your clothes. If using grey water be sure to add mulch and compost, use gypsum (displaces sodium ions), add sulphur if pH rises. Flush with fresh water if available. (For further reading see ‘Create An Oasis from Grey Water’ by Art Ludwig).

Using waste water from the bath or shower typically creates fewer problems in the garden as the products we use to wash our bodies are generally less caustic that those used in the laundry. Problems do arise however, when the bathroom is cleaned. Always ensure that waste water from the bathroom is not diverted on to the garden when cleaning, as the bleach and chlorine found in most bathroom cleaners can kill plants. The same applies if colouring your hair, using anti-dandruff shampoos and other potentially soil damaging products. A range of pure soaps and products based on natural plant extracts are available from health food stores and chemist outlets. Bathroom products from party-plan organisations like Tri Nature and pure soap distributors like Batphone Australia, are also typically safe to use on the garden. Very little information about phosphorous and dissolved salt levels can be found on bathroom products sold in supermarkets, so as a guide you should look for pure soaps and shampoos with as few additives as possible.
Simple Grey Water Precautions
Always apply grey water directly to mulched garden beds. Do not store it for later use as this will result in a dangerous build-up of e-coli bacteria and an offensive smell. Avoid spraying grey water directly onto plant foliage. Do not use it on vegetable gardens or lawns as this has the potential to bring householders in direct contact with bacteria that the grey water may contain. Never allow grey water to pool on the soil surface or run into neighbouring properties.

• Design and Management Guarantees Water Efficiency

Avoid Close Planting
Avoid the mistake of planting at close intervals to create instant landscapes. Allow each plant sufficient room to develop a good root system. Use annuals, herbs and short lived native plants to fill in the spaces until longer term plants become established. Always add compost whenever you plant. You will be providing a reservoir of moisture holding material in the soil around the roots of your plants. Think about getting the water close to the roots of new plants with devices such as the Borby Water tube.
Group Plants According To Need
Select and group plants according to their water needs. Put plants that need more regular watering close to exits, entrances and areas of activity. You are more likely to notice that they need a drink and attend to them more regularly.
Apply Soil Improving Mulch
Select mulch for its soil improvement qualities not just its aesthetics. Mulch should break down and require replacing. Decomposing mulch adds organic matter to the soil. Lucerne, pea straw, coir peat and finely chopped cane mulch are some of the best. They will help break up heavy clay, increase the water holding capacity of sandy soil, hold on to nutrients and help sustain plants in dry weather.
Consider Use Of Anti-Transpirant Sprays
Commercial anti-transpirant sprays reduce the water loss from the foliage of plants by up to 50%. Stressguard and Envy are two brands available. They can be useful when you are trying to establish new plants during dry times, when the weather is dry and windy, if you live by the sea, when you go on holidays and on plants that dry out quickly like pots and hanging baskets.
Fertilise Sparingly
Use limited quantities of organically based fertilisers so as not to create overly thirsty plants. Boost individual plants with liquid fertiliser applications. Limit applications of fertiliser to the lawn.
Water Where And When It Counts
Reduce areas dedicated to grass or accept brown lawns during long periods without rain. Learn to water plants on the basis of need and their ability to recover. Direct the water to the root zone and really soak each plant. Move the mulch, water by hand around the roots of plants and replace the mulch. Water only when plants need a drink, but water deeply at this time. Apply these strategies and you will dramatically cut water use and your garden will look better than ever!

Download PDF File (27KB) of Nambour Gardening Expo Notes 2006

Increasingly popular with new gardeners is the no-dig or sheet mulch gardening technique.  In no-dig gardens, layers of organic material are built up on the top of the soil, rather than dug into it.  Lucerne is usually used as the main component of the no-dig garden, but you can mix in other high nitrogen materials such as grass clippings and sappy green prunings with animal manure and compost.  This will make the lucerne go further.  Straw, sugar cane or some other high carbon material is used as a mulch on top of the garden.  No dig gardens can be built on top of the soil or any surface, even concrete!

Ingredients:
To build a no-dig garden 2m x 3m you will need:
Four bales of lucerne
One barrow of compost
One barrow of manure
One bale of straw/cane straw
Wet newspaper

Method:
Slash or mow any existing lawn or weeds.  Water the area well and spread some gypsum if your soil is heavy clay.  Lay down a thick layer of wet newspaper, overlapping it well.  Alternate thin layers of the lucerne, compost and manure, watering as you go.  When you have a nice thick layer almost knee high and all your nitrogen materials have been used up, spread the straw/cane mulch over the top to form a mulch layer.

Leave for at least two weeks before planting, re-wetting if necessary. Covering the bed with plastic will ‘cook’ the layers and help them to break down more quickly.

To plant the no-dig garden create small pockets within the lucerne layer and fill with compost or potting mix.  Plant seeds or seedlings into the compost pockets, drawing the straw mulch layer back in around the plants.  Leafy crops such as silverbeet, spinach and lettuce grow well in no-dig gardens as do tomatoes, melons and pumpkins.  Avoid planting root crops in no-dig gardens for several seasons until a good depth of compost has accumulated.

Water Woes
Watering is such a key factor in the growth of plants, but so many people still get it wrong.

Banana Splits
Intermittent watering has caused these bananas to split as they have matured and ripened. They are still edible, but the problem is common to many fruit trees subjected to irregular watering during fruit formation. Our bananas receive no additional watering and rely solely of rainfall, so our banana splits are a result of the seasonal rainfall patterns.

Automatic Watering Systems
If you mulch your garden to save water and have an automatic watering system installed, drippers are your best option. This is because you need to leave sprays running for a very long time if you want the water to soak through the mulch and finally through to the roots.

Two drippers per plant are best for even root growth. Rather winding the dripper line around the stem of the plant as many people do, the drippers should be pegged to emit water at the perimeter of the roots.  Always select drippers with a variable flow rate. That way you can vary the amount of water each plant receives according to its needs, the position, soil type etc.

Check the drippers for blockages regularly and test how much water plants are actually getting by placing a bucket under one or more drippers from time to time. Each plant needs to get at least 10 –15 litres of water (over a bucketful) to be of real benefit and to encourage a deeper, more drought resistant root system. Any less is really a waste of time and water.

Watering Potted Plants
Dribbling a little water into each pot is not the best way to water. You should drench pots thoroughly until water pours out of the drainage holes. If you are worried about the mess, you may need to reassess where the plants are positioned or move indoor plants temporarily to the sink or shower.

Do not make the mistake of allowing plants to sit in saucers filled with water in the hope that they will require less frequent attention. This is the quickest way to kill plants from through root rot.

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