Grow Your Own Page 6

  All of these plants come from tropical or subtropical climates, and they are not particularly well suited to frosty gardens. For cooler climates, there are some excellent Australian bush-food plants that have appeared in nurseries recently, including muntries (Kunzea pomifera), midgen berry (Austromyrtus dulcis) and narrow-leaf myrtle (Austromyrtus tenuifolia). Generally, the myrtaceous plants with edible parts are shrubs or trees that are adaptable and easy to grow provided they are in a warm climate. The most serious problem they face is myrtle rust, a fungal disease that reduces the yield by infecting both the foliage and flower buds.

  Pigface has brightly coloured flowers that catch the eye, but it’s the plant’s fruits that are edible – they taste somewhat like salty custard.

  Moraceae – the fig family This is a large and cosmopolitan family of over 1000 species, many of which are edible. The genus Ficus contains dozens of edible species beyond the common fig (Ficus carica); Australia has many native figs that were prized by Aboriginal people for their edible fruits. The other major edible group in this family is the mulberries (Morus species), of which there are several very useful species that might find a place on larger urban-farm blocks. Last but not least is the tropical genus Artocarpus, which provides two incredibly useful fruits for tropical regions: breadfruit (Artocarpus altilis) and jackfruit (Artocarpus heterophyllus).

  All of the edible members of this family are trees, and as such they are only suitable for large urban farms. However, growing techniques such as espaliering plants against a wall can make them a more practical option in smaller spaces. The members of this family are generally easy to grow in warmer climates and have relatively few problems apart from birds stealing the fruits!

  Aizoaceae – the ice-plant family A truly fascinating family of succulents, these plants have edible foliage – and, in some cases, edible flowers. The Australian plants Warrigal greens (Tetragonia tetragonioides) and rounded noon-flower (Disphyma crassifolium) are becoming popular as a source of greens for various culinary pursuits. Pigface is the common name for various species within the genus Carpobrotus that are found in coastal areas around the world. In Australia, karkalla is the Indigenous name for the species Carpobrotus rossii, and Aboriginal people ate the fruits of this plant. All species in this family are very easy to grow as well as being salt tolerant, making them suitable for both coastal and inland areas that have saline soil. Most of the species are readily propagated from cuttings and can be used as ground covers; they are ideal as fire-retardant plantings near buildings.

  Amaranthaceae – the amaranth family This has been an important group of edible plants in South America for thousands of years. Quinoa (Chenopodium quinoa) is a good example of this, and it is ironic that it has been recently ‘unearthed’ as a so-called ‘superfood’ given its long history in cultivation. Australia has a number of native Chenopodium species, known as saltbushes, which have a long history of use as food plants by Aboriginal people, and these are now being discovered by modern chefs. Various species in the genus Amaranthus have also had a long history as food plants, including the blood amaranth (Amaranthus cruentus), love-lies-bleeding (Amaranthus caudatus) and Prince-of-Wales feather (Amaranthus hypochondriacus). Another fascinating group in this family is the samphires, such as various Sarcocornia species. Amaranths are relatively easy to grow from seed, in the case of the annual types, or cuttings from the perennial types, such as the samphires. Many species are also salt tolerant, making them suitable for coastal areas and saline soil elsewhere.

  Figs were one of the first edible plants to be domesticated for horticulture, and they remain popular with urban farmers today.

  FOLIAGE FOR FOOD

  For those just starting out in urban farming, one of the simplest and most successful strategies is to concentrate on crops where the harvestable part of the plant is foliage. Crops such as lettuce (Lactuca sativa), curly parsley (Petroselinum crispum), silverbeet (Beta vulgaris) and Warrigal greens (Tetragonia tetragonioides) are very rewarding plants to grow, because there is less potential for crop losses. Even if some damage is done to foliage crops, they can still generally be used. Foliage crops are often very simple to propagate and very fast to produce. By contrast, where the final harvestable item is a fruit (including nuts, pumpkins and tomatoes, as well as sweet fruits), there is more room for damage to occur, as the plant has to produce both foliage and fruits before it can be harvested. Fruit and nut trees are often long-term crops that take up a lot more space and require more specialist growing knowledge than foliage crops.

  Cactaceae – the cactus family A famous family of succulents, these plants often feature spiny foliage. They grow well in challenging conditions, such as in arid areas or saline soil. The fleshy fruits of many cacti are edible, but not many species have been domesticated because of their relatively slow growth rates and the specialised growing conditions required. However, they certainly deserve consideration where water supplies are limited. Prickly pear (Opuntia ficus-indica) is probably the most important food crop among the cacti, with both edible fruits and foliage. The climbing cactus Hylocereus undatus is commonly marketed under the name dragon fruit, and features rather spectacular-looking fruits with a dramatic red and green colouration. Edible cacti are readily propagated from cuttings and are easily grown as long as they are not exposed to wet conditions and waterlogged soil for prolonged periods.

  Miscellaneous plant families

  There are so many more crop plants from small and unusual plant families that we could examine, particularly those from tropical and subtropical regions where plant biodiversity is at its greatest. This subject would fill a whole book on its own, and it is beyond our scope to fully explore it here. Suffice it to say that hunter–gatherer cultures all over the world spent many millennia experimenting with the plants they encountered. A relatively small proportion of the many thousands of species that have been used as food have been fully domesticated for food production. It is our view that the world needs as much genetic diversity as possible in its food-crop options. We encourage you to research this topic at every opportunity and to experiment with all the options that cross your farm-gate trail.

  CROP ROTATION

  It is generally not a good idea to grow plants that are closely related to each other in the same place year after year, as this can cause problems with pests and diseases as well as soil fertility. Read the Food Families section earlier in this chapter to see which plants are closely related. For example, tomato, eggplant, capsicum and potato are all part of the Solanaceae family and are therefore closely related to each other, but they are not closely related to the brassicas (for example, cabbage, cauliflower and broccoli) or to the cucurbits (for example, cucumber, squash and pumpkin). So ideally make a plan to rotate plants from different families around the various beds.

  Avoiding outbreaks

  We particularly recommend crop rotation for the management of pests and diseases, especially to prevent their build-up. In particular, crop rotation principles can be used to mitigate certain soil-borne problems, such as root-knot nematodes, fungal root rots and some insect pests. Particular issues are often unique to specific plant families; by rotating crops from the same plant family around different locations in the urban farm, you will greatly minimise the incidence of problems.

  Root-knot nematodes severely affect a wide range of crops, including tomato, potato and sweet potato, and it is difficult to control nematode populations where these crops are grown continuously without rotation. Maize, onion, cabbage and cauliflower are relatively resistant to root-knot nematodes, so they are excellent crops to rotate with other less-resistant plants. Grasses are also highly resistant, so lemongrass or green-manure crops of sorghum, for example, also work to reduce nematode numbers. Marigold is known to deter nematodes; it is often utilised as a companion plant, but it certainly could be used as a rotation crop.

  Crop rotation is not usually successful at controlling flying insect pests, especially in the relatively sm
all plots used in urban farming. Nor is it appropriate for perennial crops such as fruit trees. In orchards, maintain a healthy level of organic-matter content in the soil by adding compost; alternatively, plant annual green-manure crops among the trees in winter, and cut them down in early spring so they decay and feed the soil, producing disease-suppressive organic matter at the same time.

  Boosting productivity

  Another important reason for crop rotation – especially in broadacre farming – is to allow the soil to build up much-needed fertility again, particularly nitrogen fertility, by planting legume crops or clover pasture after a nitrogen-hungry crop such as maize, for example, has been grown and harvested. This consideration does not always apply in urban farming if, as we recommend, composted organic matter and fertiliser is applied as pre-plant and side-dressing applications. However, if you do not have access to these materials, then legumes are another tool in a natural-fertiliser strategy for your urban farm if you need it.

  Rotating crops allows organic matter to accumulate, for example under a pasture or green-manure crop, to help improve soil structure and physical fertility. Again, if we add composted organics regularly, this is not usually necessary in urban farms.

  Rotation is often essential in traditional zero-input farming methods, such as slash-and-burn farming and the milpa rotation system that alternates beans with squash and maize to try to slow the decline in soil fertility. The beans fix nitrogen, which is then used as mulch to improve yields of the next crop of maize or squash.

  In intensive horticulture, and particularly in urban farming, space is often very limited and rotation is not always possible, or it occurs at very considerable cost in lost production time. From a soil-fertility viewpoint, this is not a problem as compost and other organic inputs replace the necessity to build soil fertility by rotation. By importing compost, we can ensure physical fertility (including structure, organic matter and porosity) does not decline but gets better with time, and if we use nutrient-rich organic matter such as manure, or we use fertilisers intelligently, chemical fertility will not decline either.

  THE NEEDS OF PLANTS

  NUTRIENTS FOR PLANT HEALTH

  Plants require just three things to grow: sunlight and water to fuel photosynthesis, and access to a handful of elements (about 15 of the 92 naturally occurring elements). These elements are the building blocks of plants, and are classed as either macronutrients (elements that plants require in large quantities) or micronutrients (trace elements that plants require in tiny amounts). Carbon, hydrogen and oxygen are all absorbed from the atmosphere or from water; nutrients found in soil, such as nitrogen and phosphorus, are taken up by the plant through its roots, along with water.

  PHOTOSYNTHESIS – A REMARKABLE REACTION

  Carbon and one of its gases, carbon dioxide, have been getting a lot of bad press lately, but we need to rethink their importance – we must never forget that all life on Earth cannot exist without them. Through the process of photosynthesis, plants use solar energy to convert carbon dioxide from the atmosphere into carbohydrates. These carbohydrates are then used to create an astonishing array of carbon-based biochemicals, such as oils and proteins.

  The above equation for photosynthesis shows that a plant utilises the energy of the sun to force carbon dioxide and water to combine into sugars (carbohydrates), giving off oxygen as a waste product. Carbohydrates can then be used to produce the thousands of organic chemicals that make up plant bodies, or they can simply be stored (as sugar in the case of sugar cane, or as starch in potatoes).

  At night, of course, there is no solar energy, so the plant then uses the stored carbohydrates in an opposite reaction called ‘respiration’:

  Alternatively, an animal can eat the plant and use the same respiration reaction to liberate the plant’s sugars. These are then used to fuel the animal’s body, as animals cannot make their own carbohydrates through a photosynthetic process.

  A plant grows because – as long as it has adequate sunlight – it can utilise photosynthesis to create and store more carbohydrates during the day than it uses in respiration at night. If a plant’s access to sunlight is not adequate, then the plant may not produce enough carbohydrates to allow growth.

  Carbon dioxide and water are both essential nutrients for photosynthesis. For maximum growth, however, sunlight needs to be freely available as well.

  Atmospheric gases and the urban farm

  As far as we know, Earth is the only planet where the processes of photosynthesis and respiration have been developed by living organisms. Photosynthesis supplies every living thing on the planet with food, and it is responsible for increasing the amount of oxygen in our atmosphere from none to 21 per cent. It is also responsible for all the carbon-based fossil fuels (oil, coal and gas) on Earth that we are now burning and returning to the atmosphere at a rapid rate. Urban farming is a great way to take advantage of elevated carbon dioxide levels, and it helps the planet, too.

  In practice, two of the essential nutrients needed by plants – carbon and oxygen – come from the atmosphere and cannot be manipulated by farmers. We don’t really think of water as a nutrient, but it does provide the hydrogen needed to make carbohydrates during the photosynthetic reaction – so it could indeed be considered a nutrient. While we can’t easily manipulate the atmosphere and its gases, making water readily available to plants is possibly the farmer’s most important job, and it’s called ‘irrigation’. Vast effort is put into irrigation by all human societies that farm. See the Water and Drainage for more information about irrigation.

  WASTE NOT, WANT NOT

  Carbon dioxide (CO₂) is the waste product from the burning of fossil fuels, and its accumulation in the atmosphere is contributing to global warming. Fortunately for us, plants love it! Many greenhouse experiments show that if you enrich the air with carbon dioxide, the growth of plants will accelerate. It is not usually economically viable, given the cost of compressed carbon dioxide, to use this product in urban farms. However, we can take advantage of heightened levels of this gas in the atmosphere to fuel plant growth and hopefully bring a bit more balance to our planet.

  Plants in protected environments need good ventilation to ensure that the carbon dioxide supply is constantly replenished.

  NUTRIENTS SUPPLIED BY THE SOIL

  The remaining chemical elements that are essential for plant growth are all obtained from the soil (or other growing media) via the plant’s roots. In descending order of abundance, these elements are:

  nitrogen (N)

  potassium (K)

  calcium (Ca)

  phosphorus (P)

  magnesium (Mg)

  sulphur (S)

  iron (Fe)

  manganese (Mn)

  zinc (Zn)

  copper (Cu)

  boron (B)

  molybdenum (Mo).

  The essential elements for plant growth are broken down into two categories, according to the relative amounts required: macronutrients and micronutrients. It is worthwhile to consider some of the basic facts about each individual element.

  A general yellowing of foliage is often a sign of nitrogen deficiency.

  Plants that have a purplish tinge on the older leaves may be deficient in phosphorus.

  Blossom end rot of tomatoes is usually the result of major calcium deficiency.

  Macronutrients

  Nitrogen (N) is essential for green vegetative growth. A highly soluble element that is present in two forms (ammonium and nitrate), it is also one of the most expensive fertiliser elements. Nitrogen deficiency is the single most common deficiency in plants, and it is the greatest limitation to worldwide agriculture. An excess of nitrogen causes tall, floppy growth as well as poor flowering.

  Potassium (K) is particularly important for maintaining cell pressure in plants and for flowering. It is a highly soluble element sometimes called potash that is easily washed or leached from the soil by rainfall and irrigation. Wood ash is rich in potash, but it should
only be used sparingly on soil because it also has quite an alkaline pH level.

  Calcium (Ca) is especially important for shoot and root-cell growth. Many native soils are low in calcium, but urban soils often have high levels – thanks in part to the calcium-rich mortar that is sometimes left behind after building activities. As it is not particularly soluble, calcium can be a difficult element to correct if it is deficient – it is usually applied as lime or gypsum.

  THE ‘BIG THREE’

  Nitrogen, phosphorus and potassium together make up the ‘Big Three’ fertiliser requirements, and their relative proportions are given on fertiliser labels as the NPK ratio. Many fertilisers contain only these three elements, relying on the soil to supply the remaining nutrients needed by plants. These fertilisers are ideal for leafy green vegetables, which need a higher proportion of nitrogen than flowering and fruiting edible plants.

  Phosphorus (P) is vital for root growth and strong stems. Most natural Australian soils are low in phosphorus; while many of our native plants have adapted to these soils, they are often insufficient for productive farming and need to be improved. Great gains in agricultural productivity were made when the application of superphosphate became widespread.

  Magnesium (Mg) is important in photosynthesis and – like calcium – also plays a vital role in regulating the pH level of the soil. Magnesium may be applied as a solid (for example, as dolomite), which is not soluble, or in soluble form (as Epsom salts).