Grow Your Own

by Angus Stewart

  If you can possibly find an area with full sun for your garden beds, you will be rewarded with larger harvests for most crops.

  Plants can grow with less than full sunlight, provided they get a few hours of direct sunlight a day, preferably towards the middle of the day.

  On the right wavelength

  Did you know that plants only use part of the sunlight that falls on them? ‘White’ light from the sun can be split up into its constituent wavelengths by water in the air (a rainbow) or a glass prism. Remember your rainbow colours: red, orange, yellow, green, blue, indigo and violet? Plants have two kinds of pigments (chlorophylls) that are responsible for photosynthesis, namely chlorophyll a and b. Chlorophyll a uses light mostly in the blue–violet range, and chlorophyll b mostly in the red–yellow range. Both reflect green light, which is why plants appear green – they don’t need green light to photosynthesise. The human eye sees white light very well, but it is not always the best judge of the correct wavelengths or strength of light necessary for photosynthesis.

  A camera light meter is a useful guide to available light, but note that photosynthetically active wavelengths are not fully detected by these meters. Simon once used one to demonstrate that a failing indoor plant was receiving only about 2 per cent of total light input in winter, which was not enough to support growth. It goes to show that the eye is not really a good measure of available light for plants. You can see perfectly well at 2 per cent of natural light, but it would starve a plant.

  Light levels in high-density urban areas should be assessed when planning a site’s suitability for urban farming.

  What is important about light is the total amount received in a day. For example, if a plant gets four hours of full sun at around midday in winter, but was in full shadow both morning and evening, this would represent about 70 per cent of total solar input for the day, since the sun is at its most powerful around midday. This is quite sufficient for most plants. If, however, a plant receives two hours of full sun in the early morning and two hours in the late afternoon, this would only represent around 20 per cent of total solar input, as the sun is weakest at the beginning and end of the day. This is insufficient for most productive plants, but may be enough for various herbs, or, alternatively, a pretty display of ferns. If light levels are likely to be limited for an extended time, then foliage plants such as salad greens may be the best crop option.

  If you have doubts about how much sun your garden is getting, use a camera light meter. In the area where you want to grow plants, point the meter towards the sun and take a reading. Then go to a location close by that is in full sun, and take another reading. Now compare the reading from the area of interest with that from the full-sun position. For the highest productivity, you want to see a result that is better than 70 per cent of full sun in winter and 50 per cent in summer. With a result that is below these numbers, productivity will fall. Ideally you would take six readings spread over the day, from sunrise to sunset (on a clear day), and repeat the exercise four times a year, as the sun strength and day length obviously change with the seasons. It should be noted that this method doesn’t work in areas of heavy atmospheric pollution or smog, because the full sun readings are likely to be adversely affected.

  As well as not enough light, we can also be faced with the situation of too much light (and therefore heat) when growing on rooftops in cities. Full sun all day plus strong winds, particularly during summer, can lead to environments that cause plants to suffer from water stress. The solution is to shield the plants with shade cloth.

  WATER

  The total amount as well as the distribution of rain throughout the year will affect what crops you can grow. It is always worth trying to select crops that will suit your natural rainfall pattern, as supplementary irrigation can be an added cost as opposed to the free stuff from the sky. However, most high-yielding vegetables are not drought tolerant and need supplementary water.

  Surprisingly, most cities (with the exception of desert cities) have excess run-off water and should be able to support urban farming without the need to use town (potable) water supplies. This occurs because of the high percentage of sealed concrete and asphalt surfaces that results in an almost 100 per cent run-off of rainfall. In fact, due to our fear of stormwater and flooding, we have deliberately engineered vast systems to ensure that stormwater gets off our streets and into rivers and oceans as fast as possible, leaving nothing behind. This is a tragic waste, given that we have the technology to capture, store and utilise all of this water for useful purposes such as growing food.

  Thankfully, water harvesting is becoming increasingly popular in cities, and most local government areas now encourage the installation of rainwater tanks. A vision for the future involves more regionally based schemes, where run-off from roads and suburb-wide catchments is collected for redistribution as irrigation water.

  There are many different water-storage systems that can be incorporated into urban buildings to facilitate the collection of stormwater. In addition to the traditionally round above-ground tanks, there are now all sorts of other options in various shapes and sizes that can fit into the small and often-awkward spaces found in medium- to high-density urban areas. Tanks and storage structures can also be situated underneath outdoor urban areas.

  GONE WITH THE WIND

  Crop protection, such as shade cloth, can greatly mitigate the detrimental effects of wind tunnels in urban areas.

  A major problem in urban environments is the wind-tunnel effect. Buildings deflect wind, and some growing situations may suffer thanks to the high winds that are channelled their way. As well as the physical damage that high winds can cause, they can also greatly elevate transpiration. It is worth spending some time assessing your site for any potential wind-tunnel effects. Windbreaks can be used to mitigate winds; plant sturdy hedges, or use materials such as shade cloth to create a barrier.

  Water tanks now come in many shapes and sizes to facilitate water harvesting in a wide variety of urban situations.

  CASE STUDY:

  ROOFTOP FARMING

  Wendy’s Garden

  Wendy Siu-Chew Lee is a great example of an urban farmer who is exploring ways of producing food in the small spaces on top of buildings. These areas have their problems – particularly with wind, light and lack of soil – however, Wendy is determined to overcome these hurdles to cultivate as much organically grown produce as possible in her rooftop garden located in a leafy northern Sydney suburb.

  Having recently taken up the challenge of gardening with edible plants, Wendy freely admits that she is still on a steep learning curve. However, she is clearly invested in the project, and has spent considerable time experimenting with a range of growing systems and a relatively wide range of crops. This has already brought her a reasonable degree of success, as well as the odd learning experience.

  Wendy has found tremendous variation in the performance of various systems, and one of her biggest issues has been finding a potting mix that will give her reliable performance over an extended period of time. Modern potting mixes are often based on large proportions of organic components, such as composted pine bark, which continue to break down and collapse in the pot, leading to a lack of aeration. We suggested to Wendy that she should find a mix with a greater percentage of mineral components, such as horticultural ash, perlite and coarse sand, which will not collapse over time.

  Wendy uses a hungry bin worm farm to generate liquid fertiliser and solid castings that she adds to her mixes as an organic ‘tonic’ that both conditions and feeds her potting mixes. One of her recent ‘learning experiences’ was overloading her worm farm with a large quantity of overripe fruits that overwhelmed the worm population – the subsequent ‘rotten-egg gas’ smell of her unit told her that something had gone badly wrong. She has since replenished the worm population and is now careful to ensure that moist food scraps are balanced with dry, carbon-rich materials, such as shredded cardboard. Otherwise, she is enthusiastic
about the sustainable loop that is created by using worm farming to recycle the nutrients and carbon she and her partner generate each day in the kitchen.

  There are several things that Wendy has found are particularly well adapted to rooftop gardening:

  Wicking beds in the form of the Vegepod system – this is a self-contained system that has a large well of water, which means it does not need as much watering as non-wicking beds. See here in the Water and Drainage chapter for more information on wicking beds.

  Grow bags – flexible bags of potting mix with collapsible support frames for climbing vegetables, such as tomatoes and cucumbers, have proven to be an excellent way to maximise production in her limited space.

  Various containers – these are placed on castors to enable Wendy to easily move them around.

  An espaliered olive tree – this is an excellent ornamental/edible plant for one of her walls.

  A vertical garden system – this has proven to be a useful way to grow strawberries.

  The take-home message from Wendy’s garden is that experimenting with a range of growing systems is a useful way to figure out what will work in your particular rooftop, balcony or courtyard area.

  An espaliered olive tree maximises the use of limited space.

  Experimentation with various growing systems is ongoing.

  The hungry bin worm farm is perfect for generating both liquid and solid organic fertiliser from Wendy’s kitchen scraps.

  Vertical gardening is ideal for crops, such as strawberries, which benefit from being off the ground.

  Quality and quantity

  Water quality is a vital consideration, and supply must meet several criteria if sustainable production is to be achieved. Salinity must be within the limits of the species you want to grow. Salts can come from various places, depending on the source of your water. Bore and recycled water can both contain significant levels of salts that may be damaging to plant growth, and can also build up in the soil over time. Background salts can also be an issue if you want to liquid feed your plants, as fertilisers (both organic and inorganic) will further elevate the salinity of your irrigation water. On the other hand, town water and captured rainwater almost never contain excessive salt levels.

  Human pathogens can sometimes be present in recycled and harvested water supplies, and this can be a problem if you are growing crops such as salad greens. This is not because the pathogens are taken up by plants – they are not – but because salad vegetables aren’t cooked, so there is a chance that harmful microbes such as Salmonella can be ingested from the surface of the leaf. If pathogenic microbes are a problem, there are various sterilisation systems that can be used, such as ultraviolet radiation and chlorination.

  Most urban areas will be connected to a town water supply that potentially provides a source of unlimited water. However, town water is likely to be expensive, and water restrictions due to drought are increasingly common and can seriously affect water supply for plant production. It is therefore highly advisable to explore alternative water sources that can reduce dependency on town water supply.

  One of the essential roles that water plays in plants is that of carrying dissolved nutrients up through the roots to the plant. If the plant is starved of water, it will also be starved of nutrients. Conversely, waterlogged soil leads to an exclusion of air, and the roots die – literally by drowning. The issues of supplying water to your urban farm, estimating watering needs, and having sensible watering practices to avoid stressing plant-growth processes is discussed in Water and Drainage.

  GET SOME AIR

  Elevated carbon dioxide levels in cities actually help accelerate the development of fast-growing plants, such as vegetables.

  The atmosphere supplies three gases that are essential for plant growth: oxygen, carbon dioxide and nitrogen. Oxygen, at roughly 21 per cent of Earth’s atmosphere, is never a limiting factor for plant growth. In many urban areas, carbon dioxide is often elevated because of atmospheric pollution, as are other gases potentially advantageous to plants, such as sulphur dioxide. Atmospheric pollution is therefore likely to be more beneficial than harmful for urban farms, and in particular extra carbon dioxide from the burning of fossil fuels can stimulate extra photosynthesis and plant growth. Consequently, urban farming is a great way for city dwellers to mitigate their carbon footprints.

  OTHER ENVIRONMENTAL FACTORS

  The choice of crops for your urban farm will also be influenced by these impacts on the growing environment.

  Climatic extremes The potential for extreme weather events should be a part of your crop selection thinking. Hailstorms, severe frost events, windstorms and droughts are all risks that need to be managed, particularly for long-term crops such as fruit and nut trees.

  Soil type It is always a good idea to select crops that suit your soil type, otherwise you will be potentially encouraging problems such as root-rot diseases.

  Growing conditions Ensure the drainage and water- and nutrient-holding capacity of your soil is appropriate.

  Prevalence of pests and diseases For instance, the presence of fruit flies in your area may make it very difficult to grow particular fruit crops, such as stone fruits.

  Collecting rain in a tank is an excellent way of sourcing high-quality irrigation water for your urban farm.

  CHOOSING THE RIGHT CROPS

  WHAT TO GROW ON YOUR URBAN FARM

  Deciding which crops to produce is an extremely important consideration for any farm, but is particularly so for the urban farm where space is at a premium. The overall growing environment must obviously be taken into account, and decisions need to be made about whether to work with the existing conditions or to modify them to overcome environmental extremes such as frost.

  The end use of your produce will also be a factor: is it to be sold or used domestically, or a combination of the two? If you are primarily aiming at producing your own food, then the widest diversity of crops possible will give you plenty of scope for producing some food in every month of the year, while also minimising the risks of losses through pests and diseases. If, however, you are producing crops for sale, then narrowing the range down to a few crops will ensure that commercial-scale production is far more cost effective.

  FOOD FAMILIES

  The botanical world is divided into plant families based on similarities between different species, and it is no coincidence that particular families have been selected by urban farmers for millennia because of their palatability, ease of growth and adaptability to a range of growing environments. Thus, it makes sense to look at our crop choices family by family to decide what is best for our own unique urban-farm environment.

  Crop rotation is another critical concept to understand in selecting what to grow, as members of the same plant family will tend to be susceptible to the same or similar pests and diseases. Growing a variety of crops from different families and then rotating the positions in which they are grown within the urban farm helps to prevent the build-up of pests and diseases, something that is particularly important for soil-borne diseases (see here for more detailed information on crop rotation). In this context, knowledge of the major plant families that are used for food production is very useful, so let us look at them in order of their importance.

  Knowing your plant families well and rotating crops between growing beds are both critical for pest and disease management.

  HOME USE VS MARKET PREFERENCES

  Your choice of crops will be determined somewhat by whether they are to be eaten at home or sold to other people.

  The choice of what crops to grow will be governed by the overall objectives of your urban farm. The rise and rise in the popularity of farmers’ markets in recent times has created opportunities for urban farmers to obtain much higher returns for their crops than through wholesale-market channels. Specialisation in one or a few crops for sale allows for a more efficient use of resources and for some economies of scale in marketing as well as growing. The downside of this st
rategy is that specialising in one or a few crops tends to entrench the pests and diseases associated with them on your farm. However, an appropriate integrated pest management strategy as discussed in the Pest and Disease Management section is a sustainable way to meet such challenges.

  On the other hand, if the sole aim of the farm is to provide produce for the home (and to perhaps barter or donate excess yield to the local community), then our suggestion would be to grow as large a range of crops and livestock as possible. This strategy will provide the widest possible nutritional balance of major food groups for family and friends, and will also help to minimise the risk of particular plant pathogens or pests from becoming established on your urban farm.

  Fabaceae (Papilionaceae) – the legume family

  Origins With more than 19,000 species, this is the world’s third-largest plant family (after orchids and daisies). It can be found as a dominant component of virtually all types of plant communities on every continent of the planet (barring Antarctica), from tropical rainforests to dry deserts. Many of our most economically important legumes have evolved with humanity over the millennia, and they provide not only tasty food but also useful medicines (such as gum arabic), timber, dyes and natural pesticides (such as rotenone).

  Characteristics The various members of the legume family are extraordinarily diverse in growth habit. They range from small, herbaceous, bushy plants and vigorous climbers to shrubs and trees such as carob (Ceratonia siliqua), the long pods of which are used to make a chocolate substitute. This huge group of plants is arguably the most important of all for human survival, given its role in providing non-animal protein through beans and peas of various types. Pulses are a group of legumes that are harvested for their dried seeds, such as chickpeas and lentils, which are a particularly easy-to-store source of protein.