CAN I REDUCE THE NEED TO WATER MY GARDEN?
Using less water on the garden can save us plenty of money. However, more importantly, there is an obvious need for society as a whole to take responsibility for conserving our planet’s dwindling supply of fresh water. To decrease the amount of water you use in your garden, it is a matter of applying some very simple principles.
Make appropriate plant choices Plants from drought-prone climates can survive and even thrive on very little water. Australian native plants (with the exception of rainforest plants) and succulents (such as cacti) from various parts of the world are very adaptable to low water levels. It should be said, however, that drought-tolerant plants respond to higher water levels with more luxuriant growth, which will suffer if the extra water is suddenly withdrawn. It is a good idea to deep water all new plantings for the first few months to encourage an extensive root system, but then to gradually wean the plants off the extra water over a period of several months once they are well established.
Use mulch A 5–10-centimetre layer of coarse, chunky materials placed over the growing medium drastically reduces water loss due to evaporation. The best mulches for water conservation have particles that are at least 20 millimetres in diameter, and can be either organic (such as pine bark chunks or eucalypt chips) or inorganic (such as scoria or other types of gravel). See the Composting and Mulching chapter for more information.
Improve water-holding ability Well-rotted organic matter (ideally, compost made from manures and garden waste) can build up a soil’s water-storing capacity. Simply dig as much compost as you can afford into the top 15 centimetres of your soil. This will reduce the amount of water lost through run-off and drainage, and hence conserve water in the soil where plants can use it.
Scoria is an excellent choice as a permanent water-saving mulch for perennials and pots, and it looks appealing, too.
RETHINKING RUN-OFF
Many urban centres spend vast amounts of time and money ensuring that rainfall run-off is diverted quickly into rivers and oceans. What a waste of water! Sydney’s CBD and surrounds, for example – where run-off is in excess of 90 per cent due to hard surfacing – encompasses an area of about 6 square kilometres, or 600 hectares. With an average rainfall of 1200 millimetres per year, this represents a total volume of about 7200 million litres of water that heads straight into the harbour. If each square metre of urban farm requires about 300 litres of supplementary irrigation water to fill the gaps between rainfall events, then Sydney’s run-off would irrigate about 24 million square metres (or 2400 hectares) of highly productive land.
If each hectare of this productive land generated around 20 tonnes of produce per year, this equates to 48,000 tonnes of food – enough to feed just over a quarter of a million people for a year, assuming they consume around 500 grams per day of fresh fruits and vegetables.
At a smaller level, if the average house with a roof area of, say, 100 square metres is located in an area with an average annual rainfall of 1000 millimetres, then the total amount of stormwater that can potentially be collected in a year is 100,000 litres. This is a significant amount of water in relation to the needs of crops on an average suburban block, and would likely be enough to irrigate a garden of 300 square metres for a whole year in the complete absence of any rainfall.
Hose wands extend your reach into the garden when watering, and help you to direct water to specific plants.
Lots of cracks and an orange–red colour indicate that this soil has good drainage.
DRAINAGE
Plants need a constant supply of moisture, or they will wilt and eventually die. However, plant roots also need oxygen, or they will suffocate. Ironically, wilting is the first sign of waterlogging, as the roots are suffocating and cannot function to support the plant. The ideal soil for plants provides a balance between air and water – it must be well drained, but retain plenty of moisture.
So, how can you achieve this balance? At first glance, it seems impossible to have both good drainage and good moisture levels in the same soil. The answer lies in ensuring there are differently sized pore spaces within your soil. Sandy soils have large pore spaces through which water flows very freely, with little of it being retained. Clay soils have much smaller pore spaces that hold water against the force of gravity, and therefore they tend to not be free draining. Loamy soils are a mixture of sand and clay; consequently, they usually have a balance of small and large pore spaces. This gives us the best of both worlds – that is, good drainage but also adequate water storage. The perfect loam will form a ball when the moist soil is squeezed together, but this ball will break apart fairly readily when it is dropped onto a hard surface.
The effect of slope on drainage
Obviously, water runs down a slope and collects at low points. For most soil types, the greater the slope the better the drainage will be, while drainage will be poorer at the bottom of the slope. Allow for this when selecting plants for a given area of your garden or deciding whether drainage is needed.
You can use surface-drainage techniques to distribute stormwater advantageously on your urban farm – it may be possible to landscape areas such as orchards in such a way as to divert stormwater across the property. Small mounds (swales) created along the contour lines of slopes will collect water behind them, giving the water time to slowly soak into the soil and irrigate your crops.
Conversely, it is not uncommon to find areas where run-off of water occurs after rainfall, especially where there are a lot of paved surfaces, and this leads to excessive wetness in the soil. Where this happens, an interceptor drain is required. This is a simple V-shaped open trench or gutter placed between a garden bed and an upslope area that directs the water from the slope away from the growing area. The trench only needs to be shallow to divert quite a lot of water to a stormwater drain or into tanks.
Choosing plants for drainage level
Some plants have evolved in the wild to cope with poorly drained soils, but most plants are the opposite – they require a soil where water drains away within a few hours. You can save yourself an enormous amount of trouble by determining how well your soil drains and then choosing crops that will adapt to the specific conditions on your urban farm.
At one extreme are plants that grow in coastal sand dunes or deserts – they will survive and even thrive in very free-draining soils. Such species are able to cope extremely well with drought. At the other extreme are aquatic species, such as edible water lilies, which need soil that is constantly saturated. Most crop plants lie somewhere in between these extremes. By heeding the helpful advice of gardening books and magazines as to the drainage requirements of a particular species, you can avoid having to do a lot of costly and unnecessary drainage work.
WHAT CAN I DO ABOUT POOR DRAINAGE?
When we talk about poor drainage, we really mean poor soil aeration. The usual cause of poor drainage within a soil profile is an impeding layer with no air pockets, such as compacted fill, rock, poor-quality clay at shallow depth or some other impermeable barrier. If your soil is poorly drained, then there are many different interventions that can be undertaken, from the simple formation of raised beds to the more complex – and hence expensive – installation of subsurface drains.
Improve texture and structure
The first and most cost-effective choice is always going to be using and improving your own site soil. Perhaps the easiest way to make either sandy or clayey soils more loam-like and thus well drained is to add organic matter, such as well-rotted compost. Apply a layer up to 10 centimetres thick on top of the soil, and dig or fork it into the upper 15 centimetres of topsoil. Gypsum may also be required in heavy, dispersive clays.
TEST FOR DRAINAGE
Dig a hole in your soil that is 200 millimetres deep, then fill the hole with water and let it drain away. Fill it again, and time how long it takes for the water to completely drain away.
< 5 minutes = the soil is very freely drained; no action is required
5–15 minutes = the soil is moderately well drained; hilling up may help
15–30 minutes = the soil is moderately to poorly drained; raised beds are needed
30–60 minutes = the soil is very poorly drained; subsoil drainage is required
> 60 minutes = the soil is impermeable; work on soil structure, and install subsoil drains
However, even when texture and structure are close to ideal, soils can still hold too much water for a variety of reasons, such as run-off from upslope areas. In this case, you need to think about creating built-up beds or perhaps an underground drainage system.
Make raised beds
Lifting the level of the soil above the surrounding area will help get the surface soil above any poorly drained lower layers. Cultivate your soil and at the same time mound it up to whatever height is feasible; 100–200 millimetres higher than the ground level is a good start. Even digging a compacted soil with a spade or fork can often be enough to provide suitable drainage for shallow-rooted plants, such as annuals, low-growing perennials and vegetables.
Simply hilling up the soil on the ground may not be adequate for some urban areas, and you may need to create deeper raised beds that are 300–500 millimetres in height to further improve soil drainage. In this case, it will be necessary to construct some kind of retaining wall to hold the soil, using materials such as timber or masonry. Prefabricated containers, tubs and corrugated iron structures are also available for purchase from garden centres.
Raised beds are usually placed on the existing soil, and they connect to the soil layers below. From a plant-growing point of view, it’s not necessary to make raised beds any deeper than 300 millimetres – and in many cases less than this would do. However, sometimes we like to elevate the beds for convenience, so that we don’t have to break our back bending over to weed and prune plants. In this case, the bottom of taller raised beds can be filled with existing site soil to save money on purchasing high-quality ingredients.
Garden centres and landscape suppliers sell natural topsoils, as well as ‘garden mixes’ that are created by blending topsoil with compost. Either product is suitable for creating a raised bed, although it is prudent to examine a handful of any purchased topsoil to ensure that it is sandy to loamy in character, and hence will drain well.
Install subsurface drainage
Sometimes poor drainage occurs when water is trapped at the boundary between the topsoil and the subsoil, especially when the subsoil contains a lot more clay than the topsoil. This can be problematic for plants, as waterlogged soil surrounding the roots can lead to root or collar rot, and plant death. Loosening the subsoil with a pick or mattock will provide temporary relief, but the long-term solution is to provide subsurface drainage with pipes.
Doubtlessly, the best strategy is to install subsurface drainage before any new growing areas are created and sown, as it invariably requires extensive soil disturbance that will be very harmful to established plantings. It is also important to recognise that subsurface drainage is a rather technical subject that may be best left to professionals such as engineers and landscape contractors, especially if the project is large or it involves sensitive areas (for example, steep slopes or unstable soils). It is also essential to check with relevant authorities (such as the local council, as well as gas, water and electricity suppliers) if you will be digging any holes that may disturb existing underground services or change current drainage patterns.
DO I NEED TO WORRY ABOUT SUBSURFACE DRAINAGE?
If your topsoil becomes waterlogged for more than a few hours during wet weather, then it is worthwhile to spend some time investigating your soil. In several parts of your garden, dig holes that are approximately 50 centimetres deep, as this is usually the depth at which topsoil changes to subsoil, and problems can occur. Fill each of the holes with a bucket of water, and observe how long the water takes to disappear into the subsoil. If it takes more than a few hours for the water to dissipate, then subsurface drainage is highly desirable.
It is best to install subsurface drainage before planting out your urban farm, as digging the trench will disturb the plants’ growing environment.
The most effective and easiest-to-install option for subsurface drainage is corrugated plastic pipe, sometimes known as ‘ag pipe’, which is readily available from both hardware stores and garden centres. It has slots in the corrugations to allow easy entry of drainage water, and it usually features a filter sock made from fine plastic fabric to stop dirt entering and blocking the pipe over time. Unless the drainage system is likely to carry huge volumes of water, the 62-millimetre diameter pipe will be sufficient. With larger systems, these pipes join up to a 100-millimetre trunk drain in a herringbone pattern.
For general garden beds, each drain needs to be installed 500–600 millimetres below the surface. If you are going to mound the soil into raised beds, you should install the drains 300 millimetres below the surface, and then hill up the soil on top of that. For fruit trees, 700–800 millimetres below ground level is more desirable. The drains should have a slope of at least 1:70 (in other words, a fall of 1 metre for every 70 metres of length). With very heavy clay soils, the drains may need to be as little as a metre apart; if the soil is lighter, they can be up to 5 metres apart.
It is extremely important that the pipe is surrounded by a granular material – such as coarse sand, pea gravel or 10-millimetre crushed rock – to prevent it clogging with silt (even if it has a filter sock). Place a 50-millimetre layer in the bottom of your trench before laying the pipe, and then cover the pipe with a further 50 millimetres of coarse material. A useful tip in very poorly drained soils is to backfill over the gravel with sand right up to the soil surface, which will help get the excess water into the pipe more efficiently.
WHERE DOES THE WATER FROM SUBSURFACE DRAINS GO?
There are a couple of choices when it comes to diverting any excess water collected in subsurface drains. Given that water is a valuable commodity, it is a good idea to retain as much as possible on-site, particularly if you have a large garden with lots of greenery – such as deep-rooted trees and shrubs – that can use the extra water. The option here is to install an absorption (transpiration) pit similar to those that were used extensively in the past with septic systems. Dig a trench that is several metres long, a metre wide and up to a metre deep (it must be lower than the level of your subsurface drain). This trench is filled with coarse gravel, such as blue metal, and then covered with a plastic semi-cylindrical trench liner that is perforated to allow the entry of water but not sediment. The water from subsurface drains is retained in the trench during periods of heavy rain, and it gradually seeps into the subsoil when things dry out.
The second option is to divert the excess water into a stormwater outlet, if one exists on your property – check with your local council. Not every property has a stormwater outlet (for example, old inner-city properties or those that are lower than street level often have no need for one). In such cases, an absorption (transpiration) pit is the only viable option. In either case, it is important to seek advice from a plumber or landscape contractor to ensure that your system is adequately designed. If you have insufficient fall to carry the subsurface water away, then installing raised beds that are up to 500 millimetres deep may be your only choice.
INSECTS AND ANIMALS ON THE URBAN FARM
PEST AND DISEASE MANAGEMENT
Regular inspection of damage to plants and identification of the cause are vital to pest and disease control on the urban farm.
Weeds can harbour harmful insects and deadly plant diseases, so keep your garden plots as free of weeds as possible.
It would be hard to find a farmer who likes using poisonous chemicals to control pests and diseases; however, on the flip side, an environmentally friendly solution must provide adequate control, or the problem can get much worse. Harsh chemical solutions usually rely on a rapid ‘knockdown’ of pests, and they often appear to solve the problem once a
nd for all. However, this can be very misleading – the chemical often also kills beneficial predators, and this can lead to pests suddenly flourishing in the absence of their natural enemies.
Integrated Pest and Disease Management (IPDM) is a scientific approach to managing various plant problems in an environmentally sustainable way that minimises the use of toxic chemicals. The underlying principle of IPDM is using a wide variety of methods to combat a problem, so that you keep pest populations and disease damage to an acceptable level. For many pests and diseases, it will not cause too much harm to your crops if you allow some damage to occur – the trick is to stop the problem spiralling out of control. Careful monitoring is the only way to really know whether pest population levels are at stable, non-threatening levels. The bottom line is that you must learn all about the pest and utilise a variety of methods to break its life cycle if you are going to manage the problem in a sustainable way.
BEGINNING THE PROCESS
The first step in IPDM is to develop the habit of looking at your crops closely on a regular basis. Watch for any visible signs of damage or discolouration of the leaves, flowers and fruits, and then identify any insects, fungi or other pests that are lurking near the scene of the crime. Once you have identified the cause of a problem, you can then research all the ways you can stop it from multiplying and causing unacceptable damage to the crop.
Cultural methods of pest and disease control are non-chemical farming practices carried out before, during and after cropping to minimise losses. These include the removal of non-crop host plants (such as nearby weeds) that harbour pests or diseases, quarantine practices to exclude pests and diseases from the farm, selection of pest- or disease-resistant crops, and choosing disease-free propagation material such as virus-free seed potatoes. There are many other examples, but the underlying principle is that thoughtful preventative planning and action can greatly minimise the risk of economic losses.
Grow Your Own Page 24