The citrus family is characterised by perfumed flowers and the numerous translucent oil glands found in the foliage and fruits.
Cultivation requirements This popular plant family will benefit greatly from careful attention to soil preparation and selection of the most appropriate varieties for your particular environment. For instance, citrus plants vary greatly in their adaptability to frost, with cultivars such as the ‘Eureka’ lemon being much more tolerant of heavy frost than many other cultivars. Very good drainage is a particularly vital soil characteristic, as is slightly acidic conditions, because one of the most common problems in citrus is a deficiency in trace elements (such as iron and manganese) caused by alkaline conditions. Amendments of sulphur and iron sulphate are particularly important for correcting alkaline soil conditions, and the provision of extra nitrogen, phosphorus and potassium is also important as the plants in this family are generally very heavy feeders.
Pests and diseases Aphids and thrips are particularly attracted to new growth and need to be managed as much for the viral diseases they may be spreading as for the damage they do by sucking the sap of the plant. A variety of insect pests, such as citrus gall wasps, stink bugs and leaf miners, can all cause damage in various seasons throughout the year, so maintain vigilance to prevent crop losses. Fungal root diseases, such as Armillaria and Phytophthora, can potentially cause plant loss if trees are waterlogged for prolonged periods.
Brassicaceae – the crucifer or mustard family
Origins The members of this family are often referred to as ‘brassicas’. There are more than 4000 wild species in this family, with a particular centre of diversity in both Europe and Asia. Indeed, most of the important brassicas have been developed from the wild plants of Eurasia. These plants have been cultivated for centuries, and this has led to an extraordinary diversity of form and function in the various vegetables that have arisen.
Characteristics The unifying feature of this family is the crucifix-shaped four-petalled flowers (interestingly, the family was once called Cruciferae). Among the thousands of species there are not only important food plants, but also common and rather insidious weeds of disturbed areas such as roadsides and train tracks. Harvestable parts of the species include leaves, stems, flowers and seeds. Some brassicas, such as the various mustard varieties (Brassica juncea), contain significant quantities of pungent essential oils that are important condiments, but they are also grown because they exude chemicals that can control soil-borne pests such as nematodes.
Brassicas are notorious for accumulating sulphur compounds, and this can cause excessively odorous flatulence for people who overindulge in vegetables such as broccoli or cabbage. On the upside, mustard compounds are reputedly antibacterial, and mustard dressings have been used throughout history to cure wound infections.
Examples This is one of the most important vegetable families, with particular species giving rise to multiple crops. For instance, the species Brassica oleracea has given the world brussels sprouts, broccoli, cauliflower, cabbage, kohlrabi and kale. The species Brassica rapa offers vegetables as diverse as turnip, bok choy (pak choi) and tatsoi. Yet another such multifaceted species is Brassica juncea, which provides canola, mustard and mizuna. Wasabi (Eutrema japonicum), horseradish (Armoracia rusticana) and radish (Raphanus sativus) are other useful members of this family.
Something a little different from the standard lemon tree, the native Australian finger lime is now readily available as a crop plant for urban farmers.
The cabbage shows the typical form of clumping edible foliage for which Brassicaceae plants are renowned.
The crucifix-like flower shape is characteristic of Brassicaceae plants, and it gives rise to one of the common names for the family, crucifer.
Cultivation requirements Most brassicas are annuals that benefit from the supply of high levels of nutrition to fuel their rapid growth. They are generally propagated from seed and are classic cool-weather crops that should be grown throughout the autumn and winter months in most areas. As a guide, an average day temperature of 20–25°C and night temperature of 10–15°C are about right for optimum flowering and production of a wide range of brassicas. If temperatures are too warm, brassicas often run to flower before the plant fills out, a process known as bolting.
Pests and diseases Brassicas tend to be particularly susceptible to common pests such as aphids, thrips, white flies and especially white cabbage moths. Viral diseases such as cauliflower mosaic virus can be easily transferred from weedy brassica species (such as hedge mustard, Sisymbrium officinale) to vegetable crops by sucking pests such as thrips and aphids. Hungry snails and slugs are also a major problem at the seedling stage of the crops. Detailed information on dealing with these issues can be found in the Pest and Disease Management section.
Cucurbitaceae – the pumpkin or gourd family
Origins There are close to 1000 wild species – which are often known as cucurbits – in this well-known family. They are found throughout the tropical and warm-temperate regions of the world, from Africa and Europe to Asia and the Americas. The cucurbits were one of the first plant groups to be domesticated for agriculture, and they remain one of the most fascinating and important groups for the urban farmer, not least because they are very adaptable climbing plants (albeit ones that hate frost).
Characteristics This family is characterised by large, fleshy fruits (for example, melons and gourds). They are often scrambling or climbing plants with large, fleshy leaves; their showy yellow flowers are often either exclusively male or female.
Examples The family includes pumpkin, squash and gourd (Cucurbita maxima), butternut (Cucurbita moschata), zucchini or courgette (Cucurbita pepo), cucumber (Cucumis sativus), choko (Sechium edule) and various fruits, such as rockmelon and honeydew melon (Cucumis melo) and watermelon (Citrullus lanatus).
Cultivation requirements Given that they tend to have long runners, these plants need plenty of space and are best situated in spots where they can be allowed to ‘run free’. They need full sun and plenty of nutrition to reach their full potential, and they are usually susceptible to frost damage and require a protected spot in colder climates. An interesting footnote to the cultivation of cucurbits is illustrated by the competitions held to grow ‘giant pumpkins’, where specimens in excess of 200 kilograms have been recorded. This has been achieved by methods such as drip feeding the plants with the liquid from worm farming.
Pests and diseases Most species of cucurbits are susceptible to powdery mildew fungus, which needs to be carefully managed if it appears because it can often end the life of the plant. Good air movement around the plant will help stop the appearance of powdery mildew fungus in the first place. Other fungal diseases, such as Fusarium wilt, can cause the sudden death of plants, and bacterial soft rot is a threat once fruiting begins. As far as pests go, sap suckers such as white flies, melon thrips, red spider mites and aphids tend to congregate under the large, fleshy leaves and in the crevices at the base of the leaves and flower stalks – vigilance is important to ensure early intervention.
Fruits of Cucurbitaceae plants form at the base of the showy female flowers.
Like many of the fleshy fruits that are the edible part of the cucurbits, pumpkins come in all sorts of interesting colours.
The cucurbits were one of the first plant groups to be domesticated for agriculture … because they are very adaptable.
CASE STUDY:
UNUSUAL CROPS
Left to Right: Colourful gourds create ornamental interest on urban farms; Thai basil is one of several varieties the Johnstones grow.
Johnstone’s Kitchen Gardens
Tim and Liz Johnstone are part of a new breed of urban farmers who utilise small parcels of land on the immediate outskirts of cities (peri-urban areas). They supply a wide range of organically grown produce – mainly rare and heirloom vegetables, herbs and garnishes – direct to urban customers at farmers’ markets and to restaurants.
Situated in Richm
ond, on the north-west outskirts of Sydney, the Johnstones’ farm comprises several hectares of river flats with particularly sandy alluvial soil for the most part. Mushroom compost is used liberally, both as a soil conditioner and fertiliser, and does a very good job on both counts. It transforms the structureless grains of sand into a fairly rich, well-aggregated soil that holds adequate moisture and nutrients for the fast-growing mainly annual crops that Tim and Liz find to be in high demand.
Tim is particularly keen on seeking out unusual crops, from interesting heirloom varieties such as rainbow beetroot to multicoloured Amaranthus tricolor. He also looks for rare vegetables, such as the Mexican sour gherkin (Melothria scabra), salty ice plant (Mesembryanthemum crystallinum), mizuna (Brassica juncea var. japonica) and golden purslane (Portulaca oleracea). Seeds and other planting materials are sourced from overseas as well as local suppliers. Quality is emphasised over quantity, and this has won over a loyal clientele.
Another important feature of the farm is the use of protected environments and other cultural methods to extend the season for many of the crops. Poly-tunnels are utilised to modify climatic conditions in winter, when frosts can play havoc with crops grown in the open ground. In summer, covers are used to minimise the heat stress suffered by plants during the extreme maximum temperatures that prevail. Drip irrigation is the preferred method of applying moisture, as the soil tends to repel water (it becomes hydrophobic when it dries out), and a slow application rate is far better for deep penetration than using spray irrigation.
Johnstone’s Kitchen Gardens is an excellent example of a small business that is capitalising on the demand for fresh, novel, locally grown produce. People are increasingly keen on purchasing their produce at farmers’ markets, where they can deal directly with and establish a personal relationship with growers. Buyers can then be sure that they are getting truly organic produce every time.
Mizuna (Brassica juncea var. japonica) has a wonderful texture; Malabar spinach (Basella alba) is an unusual climbing leafy green vegetable
Mexican sour gherkin (Melothria scabra) is a miniature relative of the cucumber.
The edible foliage of Amaranthus tricolor can add vibrant colour to salads.
Minor food families
As well as the major plant families listed earlier, there are many minor contributors that are incredibly important in providing diversity in the planet’s food supply. Our advice is to experiment with and grow as wide a variety of crops as possible in your urban farm, including plants from both major and minor food families. Here is an abbreviated rundown of some of the minor plant families and their more important species that provide valuable biodiversity among crops.
The globe artichoke is a particularly ornamental edible member of the daisy family.
Orchidaceae – the orchid familyThis family encompasses around 28,000 species, but surprisingly contributes only a handful of edible species to agriculture and horticulture. The seed pod of the vanilla orchid (Vanilla planifolia) is the most important crop, but the plant requires tropical growing conditions. Aboriginal people ate the tuberous roots of a number of native ground orchids, but these plants are probably a bridge too far for growing in urban farms.
HEIRLOOM CROP VARIETIES VS MODERN PLANT BREEDS
Agriculture and horticulture evolved through the selection of genetically improved plants and animals, leading to established ‘breeds’ that have been handed down for generations. These are now often referred to as ‘heirloom’ or traditional varieties because of their long history in cultivation. Modern industrial-scale agriculture and horticulture has (very sadly in our view) led to the demise of many traditional ‘breeds’ of plants and animals that were often very well adapted to the specialised environments in particular regions.
F1 hybrids are a particular type of hybrid seed that is produced by crossing inbred seed lines. This complicated process is usually only feasible for large commercial seed companies because of the expensive hand-pollination methods involved. Such hybrids show more vigour than their parents, but they do not breed true. Seeds from them will either be sterile or will produce offspring with characteristics like their parents.
One of the more controversial subjects regarding food production in recent times has been the introduction of GMOs (genetically modified organisms) to large-scale farming. The term GMO is usually reserved for a plant or animal that has been produced through genetic engineering, where particular genes are transferred from one organism to another.
Our view on GMOs is that the jury is still out on their long-term effects on the environment and consumers. However, their widespread use in industrial-scale agriculture and horticulture means that a worldwide experiment is already underway that will tell the story one way or another over the longer term. In the meantime, the urban farmer has an abundant biodiversity of crop choices, and, as such, we should be exploring all the options that help to preserve the amazing genetic diversity that we have built up over thousands of years. It is an absolute certainty that climate change will require us to increasingly employ traditional techniques of plant selection and breeding; if we allow heirloom varieties and undeveloped and potential wild-food plants to disappear from the planet, it will be at our peril.
We would encourage urban farmers everywhere to look at heirloom varieties first, but also to consider modern plant varieties – because many of these have been bred by traditional techniques that have served humanity well for thousands of years. In other words, consider each plant variety on its origins and merits when choosing what to grow. And, wherever possible, introduce a mixture of crops and varieties to help preserve genetic diversity in our food crops for the benefit of future generations.
Asteraceae – the daisy family With over 32,000 species, this family has contributed a few very useful edible plants. Lettuce (Lactuca sativa) and sunflower (Helianthus annuus) – and their close relative, the Jerusalem artichoke (Helianthus tuberosus) – are the stand-out crops, despite the latter’s ability to cause a great deal of flatulence in people after the delicious tubers are consumed. Herbs from the family – such as yarrow (Achillea millefolium), purple coneflower (Echinacea purpurea) and dandelion (Taraxacum officinale) are easily grown – and they are excellent choices for attracting pollinators such as bees to production areas.
Lamiaceae – the mint family It is instantly familiar because most of its members are rich in essential oils. The plants also feature square stems and distinctively tubular-shaped ‘labiate’ flowers that have a prominent lip at the bottom. The family includes many of our most popular culinary and medicinal herbs, such as peppermint (Mentha x piperita), thyme (Thymus vulgaris), sage (Salvia officinalis) and oregano (Origanum vulgare). Found all over the world, particularly in moist environments such as riverbanks, this family has numerous Australian members – not the least of which is river mint (Mentha australis), which was used by Aboriginal people for both culinary and medicinal purposes.
Although it provides very little bulk in our food supply, the mint family is nonetheless one of the most useful of all food plant groups for the urban farmer. The plants take up very little space and are very good at attracting pollinators. Many are long-term perennials that propagate very easily by division of the clumping or running stems. It is a good idea with some of the more rampant species, such as the mints, to contain them in beds where they cannot spread at will.
Amaryllidaceae – the amaryllis family This is an interesting group, because the plants in it feature true bulbs (as opposed to tubers or other underground plant parts). The largest group of edible bulbs in the botanical world, it includes the following species: onion (Allium cepa), chives (Allium schoenoprasum), garlic (Allium sativum) and leek (Allium ampeloprasum). All of them form clumps with pungent, linear, grey–green leaves and terminal clusters of mauve or purple lily-like flowers.
The amaryllis family is very easy to grow and is great for frosty climates, as the bulbs can be planted deep enough so that they are insulated against the wors
t of the cold. Usually the bulbs or seeds of the crops are planted in autumn and harvested in late spring or early summer, but in milder climates most species can be grown throughout the year. The family is generally free of pest and disease problems, but does require deep, well-drained soil to optimise the yield and to prevent rotting if wet periods are experienced.
The distinctively shaped flowers of the mint family are instantly recognisable.
Zingiberaceae – the ginger family As well as ginger (Zingiber officinale), other very useful edible members of this family that are readily grown on urban farms include galangal (Alpinia galanga), turmeric (Curcuma longa) and cardamom (Elettaria cardamomum), whose seeds provide one of the world’s most sought-after spices. The family is spread across tropical and subtropical areas of the world, but the various edible members can be grown successfully in warm-temperate climates as well. For most species, the edible rhizomes (underground stems) grow actively throughout the warmer months of the year and are then harvested in autumn. As well as a warm, frost-free climate, the plants generally require a free-draining situation and a high level of nutrition during their growing season (spring to early autumn).
Myrtaceae – the myrtle family It is perhaps best known for its essential oils, a characteristic of the family that can often be observed as translucent oil glands when a leaf is held up to the light. Oils obtained from the leaves of gum trees (Eucalyptus species) and tea-trees (Melaleuca species) are some of the world’s best botanical disinfectants, and they also provide unique culinary flavours. In addition to the essential oil-producing members of the family, there are also a number of species that produce beautiful fruits, including various lilly pillies (Syzygium species) from Australia and Southeast Asia, and the feijoa (Acca sellowiana) from South America.
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