Geographic factors influencing American garden design and landscape architecture
America is a large country, and no one can gain any comprehension of the garden-making problem there without due consideration of factors of geography, topography and climate. In latitude and longitude the inhabited portions of North America cover a territory equal to the British Isles, all of Western Europe, all Eastern Russia, one-half of Siberia, and the whole Mediterranean Basin, including Turkey, Persia and Northern Africa. If it is necessary, in writing of European gardening, to discriminate carefully such areas as Italy, Germany, Russia and Great Britain, it is equally necessary to examine the peculiarities of California, Florida, the Mississippi Basin, New England and Canada in speaking of gardening in North America.
Aside from its mere physical vastness, this North American continent has a highly varied topography. Beginning at the eastern seaboard there is found a narrow coastal plain marked by low hills, often rocky. Back of this lies the geologically old Appalachian mountain range, heavily wooded and watered, and in its northern reaches strongly glaciated. Next comes the Mississippi valley, very wide, generally level, considerably varied in its soil but largely of limestone derivation, exceedingly fertile and mostly well cultivated. The eastern two-thirds of this basin has an ample rainfall, ranging roughly from twenty- five to thirty-five inches annually. The western third verges toward arid conditions, the rainfall diminishing westward to the Rocky Mountains. In this system of high mountains is found a remarkable range of physical conditions, varying from narrow, sunny, fertile, well-watered valleys to arid steppes and mountain peaks capped with eternal snow. West of the Rocky Mountains lies the great interior plateau, about the size of France and comprising several states. The elevation ranges from 2000 to 6000 feet above sea-level, with many local mountains running considerably higher, a few up to 10,000 feet. Rainfall is deficient, but a few small areas under irrigation are highly fruitful. This brings us to the Sierra Nevada range, almost as high as the Rockies and perhaps more picturesque. These mountains are heavily wooded on their western slopes but nearly arid on their eastern side. Between them and the Pacific Ocean lie the rich, varied and mild areas of the Pacific slope in British Columbia, Washington, Oregon and California. Here the rain- fall is generally heavy, especially northward, forests are made up of enormous trees and crowding undergrowth, and the climate is much milder than in corresponding latitudes eastward. This amelioration of the Pacific Coast climate by the warm ocean currents from Japan is a factor of commanding importance.
This glance from the Atlantic to the Pacific Coasts necessarily ignores many local conditions of great importance. And it leaves the necessity of retracing steps to speak of Canada at the north and the Gulf States at the south. It is true that, in general terms, the topographic features just sketched extend northward across Canada; true also that, lying farther north, each Canadian zone has a slightly shorter growing season and a lower summer temperature than the corresponding zone in the United States. Yet Canada is a highly fertile arable area, and has a large population of cultivated citizens who have made great progress in horticulture and landscape architecture. The areas bordering on the Gulf of Mexico constitute another zone of quite individual qualities. This zone includes the whole of Florida, with portions of Alabama, Mississippi, Louisiana and Texas. Altitudes are low, usually hardly above tide-level, the surface is flat, and there is much swamp land. There is naturally much heavy forest in which southern species of pine are conspicuous. Rainfall is ample and the temperature is warm and equable.
Emphasis must be placed upon the fact that these large areas represent major physical subdivisions of the continent, characterised by substantial differences of soil, rainfall, altitude or temperature, such as exert a determining influence upon plant culture. Nor may the complementary fact be overlooked that within these areas lie many smaller sections with very diverse conditions. The full development of local possibilities under these peculiarities has not, generally speaking, been accomplished in America, perhaps from lack of time; and this lack of intensive local refinement is one of the distinguishing characteristics of American horticulture as compared with that of Europe. In America, where everyone from coast to coast buys the same manufactured articles, reads the same garden magazines, and patronises the same nurseries, and where they even buy standardised ready-made houses from mail-order merchants, the tendency toward uniformity is very strong and the development of local specialities is correspondingly impeded.