Grow Your Own

by Angus Stewart

  Cereal straw or hay is a low-cost mulch that is easy to apply over large areas, but it can cause nitrogen drawdown.

  A carpet of mulch insulates the soil, protecting the fragile roots of these seedlings from extremes of temperature.

  WATER AND DRAINAGE

  A DELICATE MOISTURE BALANCE

  One of the keys to successful food production is a continuous supply of water that is of sufficient quality for the plants that are being cultivated. Water for crop irrigation does not necessarily need to be of the same standard as drinking water, so it can be derived from a variety of sources. It is important to explore the best way to supply your water needs in terms of quantity, quality and cost. Equally vital is to ensure that your soil does not become waterlogged, as this will kill plants if it continues for too long. Creating a growing environment that is well drained yet holds enough moisture for crop growth is a major part of urban farming.

  WHAT ARE YOUR WATER RESOURCES?

  Most urban areas will be connected to a town water supply that provides a source of more or less unlimited water, but this will often come at a substantial monetary cost so it is obviously advisable to not rely solely on it if possible. It is therefore worth exploring alternative water sources that may provide a lower-cost option. The capital cost may be significant when setting up systems such as rainwater tanks or bores, but you are likely to save an enormous amount of money in the long term, as well as reduce your dependence on expensive town water, which may be of variable quality.

  Your water supply must be of appropriate quality if sustainable crop production is to be achieved. The most critical point is that salinity (the concentration of dissolved salts in the water) must be within the limits of the species you want to grow. The salinity level varies depending on the source of your water. Rainwater will generally have negligible salinity, and town water in most areas will not be a problem; however, bore and recycled water can both contain significant salt levels that may damage plant growth, and can cause the build-up of salts in the soil over time. If you are in any doubt about the quality of your water, then you should get it tested by a reputable laboratory that can hopefully also advise you on any treatment measures that may be needed to improve the quality.

  Background salts can also be an issue if you liquid feed your plants, as fertilisers (both organic and inorganic) will further elevate the salinity of your irrigation water. If you have a salinity problem, then it is worth learning more about this topic and perhaps investing in a salinity meter so that you can monitor your soil and water.

  Roof-water harvesting and storage tanks are a practical way of reducing your dependence on purchased town water for your urban farm.

  HOW MUCH WATER WILL I NEED?

  If you do not have access to town water, then it is critical that your water-storage facility – whether it is a small tank or a large dam – is sufficient to get your urban farm through dry spells or droughts. The amount of water you will need depends on the size of your growing area and how intensively you are using it throughout the year. Other considerations include whether you are growing outdoors (and therefore utilising rainwater when it falls) or under some sort of cover, such as a greenhouse; soil type (how much water does your soil store?); and crop types (some will use much more water than others).

  Plants grown in terracotta pots need to be watered often, as water is lost through the porous pot. This does not occur with plastic pots.

  WATERING RESTRICTIONS

  Inexpensive timers take much of the work – not to mention guesswork – out of irrigation, especially during drought periods.

  At any time in Australia – summer or winter – harsh drought conditions can overtake us. This results in local authorities imposing strict restrictions on when and how we water our gardens and urban farms. If you are in any doubt about this issue, it is best to check with your local council or water authority, as fines for breaking the rules can be substantial. At times like these, an additional water source such as a tank or dam will be worth its weight in gold.

  HOW OFTEN SHOULD I WATER MY CROPS?

  The water requirements of any given crop on your urban farm are constantly changing. Your plants will obviously require much more water on hot or windy days, when they are actively growing and flowering, and when they are growing in soils that do not store moisture well. The depth of a plant’s root system will also affect its ability to extract moisture. Plants will extend their root systems to seek out moisture in the subsoil, and we can encourage this through deep watering every few days to a week if there has been no additional moisture through rainfall or run-off.

  Plants in containers will usually need to be watered more frequently, as less water is stored in the limited volume of potting mix than in a garden bed. Your choice of soil or growing medium (such as potting mix) also impacts on watering frequency due to variations in water-holding capacity.

  HOW MUCH WATER DO I NEED TO APPLY?

  The amount of water to apply when you irrigate your crops will depend on your soil depth and type as well as the variety of crop that you are growing. A practical way of telling how much water is needed is to apply a set amount of water over 1 square metre – or leave the sprinklers on for a known time – then wait 24 hours before digging a hole to see how far down the soil profile or potting mix the water has reached. If it has only penetrated 100 millimetres, then you know that to penetrate 200 millimetres (which is about right for vegetables) you will need to use twice as much water, or to water for twice as long. The depth of the wetting front (or depth of penetration) is seen more clearly if the soil is a bit on the dry side to start with. It is particularly important in saline soils that you irrigate deeply each time you water, as this carries the salts down the profile so they are not in range of plant roots.

  A granular wetting agent dug in to the surface of your soil will help reduce water repellence.

  Using light-coloured mulches, such as white pebbles, on your garden beds will keep soil cool and conserve precious moisture.

  WHEN SHOULD I WATER MY CROPS?

  It is often stated that you should not water plants during the heat of the day. This is not necessarily true. It you water as we suggest – watering deeply but less often, rather than doing it lightly and frequently – then the evaporative losses are negligible. We agree that on hot, windy summer days, a lot of water can be lost by evaporation. However, when plants are highly stressed on very hot days and start to wilt, our advice is to cool them down with a big watering, just like you would hose the kids or the dog.

  Watering plants very early in the morning during autumn and winter will help prevent frost damage to your crops. If you don’t relish getting up before the sun, use an irrigation timer – set it to start at 3 am, and to turn off and on for the next two hours.

  WATER-REPELLING GROWING MEDIA

  Some soils (especially those that are very sandy) and even potting mixes actually repel water – water droplets form little spheres on the surface of the growing medium, and they enter only after minutes or hours, often resulting in erosion problems. Water is often channelled down cracks, leaving the growing medium totally dry in parts even after a considerable amount of water has been applied to the surface. If you believe that your growing medium is repelling water, there are two remedies:

  Soil-wetting agents There are a number of products available, such as Wettasoil®. These are made up in a watering-can and showered over the affected growing medium as required. After their use, water is attracted to the growing medium rather than being repelled. SaturAid® is another wetting agent, but in this case the product comprises granules that are mixed through the growing medium.

  Mulches Water repellence is at its worst when a susceptible growing medium becomes very dry. Applying a suitable mulch will conserve moisture, greatly reducing the possibility of the growing medium drying out and subsequently being difficult to re-wet. Light-coloured inorganic mulches, such as white gravel, are ideal because they do not heat up as much as dar
k mulches; they also let in the maximum amount of water, because they do not absorb moisture as it flows through (unlike organic mulches, such as woodchips). On sloping sites, where water can run off and cause erosion, mulches are particularly important because they help to hold moisture on top of the growing medium while it gradually soaks in.

  TYPES OF WATERING SYSTEMS

  There are many different types of watering systems. Choose the one that best suits the size of your urban farm, the crops you are growing as well as your budget and time constraints.

  Drip irrigation Small emitters that release droplets of water at regular intervals are inserted into flexible plastic pipes, which are then laid along the ground close to the plants. Various emitters are available, depending on how many litres per hour are required. If you have extensive areas to water, then they often need to be divided up into sections that are watered consecutively; in this case, you will want to release water more quickly. Smaller areas can be comfortably watered more slowly. Drip irrigation is the most efficient watering system, as the water goes directly into the soil and there is no chance of it evaporating into the atmosphere (which happens with sprinkler systems). It is also particularly well suited to plants that do not have extensive root systems, such as annuals and vegetables.

  Sprinkler systems These systems have outlets that spray water into the air, and the water then falls to the ground like gentle rain. Significant amounts of water are lost to evaporation, particularly on hot and/or windy days. However, the advantage of sprinkler systems is that very large areas can be blanketed with water at any one time. This makes them particularly suitable for lawns, for instance. There are various options, from the familiar moveable sprinklers to fixed sprinklers that sink down into the soil when not in use (known as ‘pop-up’ sprinklers). Another extremely useful variation is the micro sprinkler. A number of these can be plugged into a flexible pipe (in the same way that drip emitters are installed), and they can be used to water intermediate areas (such as the drip line of trees and shrubs) without losing too much water to evaporation.

  Drip-irrigation systems are ideal for the water-conscious urban farmer, as they direct the moisture straight into the soil.

  When using drip irrigation, it is essential that you install a filter to prevent blockages.

  Watering by hand is labour intensive, but it is often necessary to allow you to target new transplants.

  Capillary watering (wicking beds) You may have heard about wicking beds as a way of growing edible plants. They allow us to water plants from below; water rises towards plant roots because its attraction to soil particles outweighs the force of gravity trying to carry it downwards. The distance that water can rise depends on how fine the soil particles are – water can rise much further in a clay soil than in a sandy one. Thus, if you want to use this form of irrigation, it is vital to understand how it works and to design a system that will supply the amount of water that is needed. Capillary watering has several advantages over watering from above:

  It keeps the foliage dry, so it is less prone to diseases.

  Plant roots are trained to go down to where the water and nutrients are.

  Plants can take up as much water as they need to grow at their maximum rate.

  It is much harder for plants to dry right out.

  However, it is important to have a water supply that is free of pathogens, as problems such as root rot can spread very easily from plant to plant in the shared water of a capillary system. In addition, fertiliser salts can build up because there is no flow of water through the growing medium to flush any excess salinity away. If plants start to show symptoms such as burning on the margins of the leaves, then it is time to renew the growing medium. An alternative is to install a plughole in the base of the system that allows you to flush out the growing medium every few months or if a salt build-up becomes apparent.

  Hand-watering The time-honoured method of standing with a hose and watering your garden is always an option, but of course it is very labour intensive. There is also a tendency to not apply enough water when we use a hose, as it takes quite a number of minutes to deliver enough water to most soils so that it reaches right down to the bottom of the root zone. One big advantage of hand-watering is that we can use the so-called ‘weed and feed’ method; a clip-on container is attached to the hose that allows you to easily liquid feed and apply herbicide to very large areas, particularly lawns, as you water them.

  ENSURING YOUR IRRIGATION SYSTEM IS SAFE

  Do-it-yourself irrigation systems for the garden are readily available, and they usually come with step-by-step installation instructions that any average home handyperson with a modest toolbox can follow. Some manufacturers have even produced videos to help you through the whole process. If you have any concerns or queries, distributors of irrigation equipment – such as hardware stores and garden centres – are excellent sources of advice and information.

  If you are installing a permanent irrigation system that will be left constantly attached to a water outlet, then special precautions need to be taken to prevent the possibility of what is known as backflow. This can occur if broken pipes or other problems interrupt the mains water supply. If there is water in your irrigation system, it can flow back into the pipes and contaminate the mains water supply. Manufacturers of irrigation equipment can provide useful information and hardware to help you avoid this problem, or you can seek specialist advice from a plumber.

  CASE STUDY:

  VEGEPOD

  You can set up neat rows of Vegepods, with each one growing a different crop.

  The Vegepod is an innovative Australian-designed growing system that is perfectly suited to urban farming, as it uses a capillary watering system in a lightweight and transportable unit. It is covered with a ‘greenhouse’ frame that both shields the crops inside from any climatic extremes and protects the plants from the ravages of pests and diseases. A large reservoir of water situated beneath the plants is accessible to the roots at all times, which is particularly handy as the plants grow bigger and thirstier or if you accidentally forget to water the plants for a few days.

  It is certainly possible to make your own capillary system (wicking beds) from recycled materials, such as corrugated iron tanks or old fruit-picking bins; however, if you are not a handyperson, then a ready-made unit such as the Vegepod provides a practical alternative.

  CASE STUDY:

  SCHOOL FARMING

  Bonbeach Primary School Garden

  The proliferation of school gardens around Australia has been an incredibly important part of the urban-farming movement in recent years. Primary-school children are particularly receptive to learning about the basics of growing their own food and keeping chooks. Many city children live in medium- to high-density housing where opportunities for gardening are often very limited or even non-existent, so school grounds are one of the few places where they can get stuck into some serious food production. As many parents and teachers have found, however, the challenge is not so much in creating a school kitchen garden as it is in maintaining the necessary level of care and enthusiasm in the years after a project has been launched.

  Bonbeach Primary School is located on Port Phillip Bay, in the south-eastern suburbs of Melbourne. The school’s garden and its associated parent-led garden group, the Growing Green Thumbs, run by Amy Dowling and Jade Kavanagh, provide an excellent model for creating a sustainable school-based urban farm that successfully engages with the local community on an ongoing basis. Amy and Jade also run workshops for students and the wider community on a variety of topics beyond food gardening, such as nature-play structures, worm farms, teepees, frog bogs and mud pits.

  The garden has largely been created on areas of asphalt within the school grounds by the construction of raised beds. A conscious decision was made to publicise the project and seek community help, and this has led to many donations of materials (such as potting and soil mixes), equipment (such as worm farms and wicking beds, including the Ve
gepod system) and expertise in the form of professionals donating time for education and input into the garden.

  The school has balanced the need for security in the school grounds with the concept of a community garden by placing some garden beds outside the school grounds – families can access these outside school hours. It also invites locals to the Bonbeach Farmers’ Market, which is held at the school on the second Sunday of every month. The market raises funds for the school and its garden by selling the produce from the school as well as other novel products, such as ‘Worm Wee’ fertiliser sold in recycled 2-litre milk bottles.

  The Bonbeach Primary School Garden is just one example of a school-based urban farm functioning successfully within an Australian city, and its website (www.bonbeachpsgreenthumbs.weebly.com) is full of useful information and ideas for those who might like to start a similar project at their school. There are, of course, other highly successful models, with perhaps the best known being the Stephanie Alexander Kitchen Garden Program, which links cooking with the production of fresh fruits and vegetables. In our observation, the leadership of fully committed parents, teachers and other professional staff greatly enhances the chances of success of whatever style of program is chosen. A succession plan to ensure that leadership is passed on as students and parents graduate from the school is also highly advisable.

  Fruit trees combine beautifully with ornamentals in above-ground timber-edged raised beds.

  A wide variety of vegetables, grains and herbs is grown at Bonbeach Primary School

  Community spirit and shared endeavour is an important ingredient in urban farming

  Children learn about all aspects of planting out and garden maintenance.