Agricultural Regions
Temperate zones
Temperate zones for horticulture cannot be defined exactly by lines of latitude or longitude but are usually regarded as including those areas where frost in winter occurs, even though rarely. Thus most parts of Europe, North America, and northern Asia are included, though some parts of the United States, such as southern California and Florida, are considered subtropical. A few parts of the north coast of the Mediterranean and the Mediterranean islands are also subtropical. In the Southern Hemisphere, practically all of New Zealand, a few parts of Australia, and the southern part of South America have temperate climates. For horticultural purposes altitude is also a factor; the lower slopes of great mountain ranges, such as the Himalayas and the Andes, are included. Thus the temperate zones are very wide and the range of plants that can be grown in them is enormous, probably greater than in either the subtropical or tropical zones. In the temperate zones are the great coniferous and deciduous forests: pine, spruce, fir, most of the cypresses, the deciduous oaks (but excluding many of the evergreen ones), ash, birch, and linden (lime).
The temperate zones are also the areas of the grasses—the finest lawns particularly are in the regions of moderate or high rainfall—and of the great cereal crops. Rice is excluded as being tropical, but wheat, barley, corn (maize), and rye grow well in the temperate zones.
Plants in the temperate zones benefit from a winter resting season, which clearly differentiates them from tropical plants, which tend to grow continuously. Bulbs, annuals, herbaceous perennials, and deciduous trees become more frost-resistant with the fall of sap and therefore have a better chance of passing the resting season undamaged. Another influence is the varying length of darkness and light throughout the year, so that many plants, such as chrysanthemums, have a strong photoperiodism. The chrysanthemum flowers only in short daylight periods, although artificial lighting in nurseries can produce flowers the year round.
Most of the great gardens of the world have been developed in temperate zones. Particular features such as rose gardens, herbaceous borders, annual borders, woodland gardens, and rock gardens are also those of temperate-zone gardens. Nearly all depend for their success on the winter resting period.
Wild Flowers in Tuscany
Tuscany is especially flowery, being wetter than Sicily and more homely than the Roman hills. Tuscany manages to remain so remote, and secretly smiling to itself in its many sleeves. There are so many hills popping up, and they take no notice of one another. There are so many little deep valleys with streams that seem to go their own little way entirely, regardless of river or sea. There are thousands, millions of utterly secluded little nooks, though the land has been under cultivation these thousands of years. But the intensive culture of vine and olive and wheat, by the ceaseless industry of naked human hands and winter-shod feet, and slow-stepping, soft-eyed oxen does not devastate a country, does not denude it, does not lay it bare, does not uncover its nakedness, does not drive away either Pan or his children. The streams run and rattle over wild rocks of secret places, and murmur through blackthorn thickets where the nightingales sing all together, unruffled and undaunted.
It is queer that a country so perfectly cultivated as Tuscany, where half the produce of five acres of land will have to support ten human mouths, still has so much room for the wild flowers and the nightingale. When little hills heave themselves suddenly up, and shake themseles free of neighbours, man has to build his garden and vineyard, and sculpt his landscape. Talk of hanging gardens of Babylon, all Italy, apart from the plains, is a hanging garden. For centuries upon centuries man has been patiently modelling the surface of the Mediterranean countries, gently rounding the hills, and graduating the big slopes and the little slopes into the almost invisible levels of terraces. Thousands of square miles of Italy have been lifted in human hands, piled and laid back in tiny little flats, held up by the drystone walls, whose stones came from the lifted earth. It is a work of many, many centuries. It is the gentle, sensitive sculpture of all the landscape. And it is the achieving of the peculiar Itaian beauty which is so exquisitely natural because man, feeling his way sensitively to the fruitfulness of the earth, has moulded the earth to his necessity without violating it.
Which shows that it can be done. Man can live on the earth and by the earth without disfiguring the earth. It has been done here, on all these sculptured hills and softly, sensitively terraced slopes.
But, of course, you can't drive a steam plough on terraces four yards wide, terraces that dwindle and broaden and sink and rise a little, all according to the pitch and the breaking outline of the mother hill. Corn has got to grow on these little shelves of earth, where already the grey olive stands semi-invisible, and the grapevine twists upon its own scars. If oxwn can step with that lovely pause at every little stride, they can plough the narrow field. But they will have to leave a tiny fringe, a grassy lip over the drystone wall below. And if the terraces are too narrow to plough, the peasant digging them will still leave the grassy lip, because it helps to hold the surface in the rains.
And here the flowers take refuge. Over and over and over and over has this soil been turned, twice a year, sometimes three times a year, for several thousands of years. Yet the flowers have never been driven out. There is a very rigorous digging and sifting, the little bulbs and tubers are flung away into perdition, not a weed shall remain.
Yet spring returns, and on the terrace lips and in the stony nooks between terraces, up rise the aconites, the crocuses, the narcissus and the asphodel, the inextinguishable wild tulips. There they are, for ever hanging on the precarious brink of an existence, but for ever triumphant, never quite losing their footing. In England, in America, the flowers get rooted out, driven back. They become fugitive. But in the intensive cultivation of ancient Italian terraces, they dance around and hold their own.
D. H. Lawrence, Flowery Tuscany
Tropical zones
There is no sharp line of demarcation between the tropics and the subtropics. Just as many tropical plants can be cultivated in the subtropics, so also many subtropical and even temperate plants can be grown satisfactorily in the tropics. Elevation is a determining factor. For example, the scarlet runner bean, a common plant in temperate regions, grows, flowers, and develops pods normally on the high slopes of Mt. Meru in Africa near the Equator; it will not, however, set pods in Hong Kong, a subtropical situation a little south of the Tropic of Cancer but at a low elevation.
In addition to elevation, another determinant is the annual distribution of rainfall. Plants that grow and flower in the monsoon areas, as in India, will not succeed where the climate is uniformly wet, as in Bougainville in the Solomon Islands. Another factor is the length of day, the number of hours the Sun is above the horizon; some plants flower only if the day is long, but others make their growth during the long days and flower when the day is short. Certain strains of the cosmos plant are so sensitive to light that, where the day is always about 12 hours, as near the Equator, they flower when only a few inches high; if grown near the Tropics of Cancer or Capricorn, they attain a height of several feet, if the seeds are sown in the spring, before flowering in the short days of autumn and winter. Poinsettia is a short-day plant that may be seen in flower in Singapore on any day of the year, while in Trinidad it is a blaze of glory only in late December.
In the tropics of Asia and parts of Central and South America the dominant features of the gardens are flowering trees, shrubs, and climbers. Herbaceous plants are relatively few, but many kinds of orchids can be grown.
Vegetable crops vary in kind and quality with the presence or absence of periodic dry seasons. In the uniformly wet tropics, the choice is limited to a few root crops and still fewer greens. Sweet potatoes grow and bear good crops where the average monthly rainfall, throughout the year, exceeds 10 inches (25 centimetres); they grow even better where there is a dry season. The same can be said of taro, yams, and cassava. Tropical greens from the Malay Peninsula are not as good as those grown in South China, the Hawaiian Islands, and Puerto Rico. They include several spinaches, of which Chinese spinach or amaranth is the best; several cabbages; Chinese onions and chives; and several gourds, cucumbers, and, where there is a dry season, watermelons. Brinjals, or eggplants, peppers, and okra are widely cultivated. Many kinds of beans can be grown successfully, including the French bean from the American subtropics, the many varieties of the African cowpea, and yard-long bean. The yam bean, a native of tropical America, is grown for its edible tuber. In the drier areas the pigeon pea, the soybean, the peanut (groundnut), and the Tientsin green bean are important crops. Miscellaneous crops include watercress, ginger, lotus, and bamboo.