numerous groups of cultivated and wild plants, including representatives of various plant families. Ornamental plants are used to provide greenery in cities and other inhabited areas, in gardens and parks, and outside of public buildings and residences. They are distinct because of their attractive shapes and the different colors of their flowers, leaves, and fruits. In terms of biological properties and agrotechnical requirements, ornamental plants are divided into several groups, such as trees and shrubs, perennials, biennials, annuals, grasses, and bulbs.
Ornamental trees and shrubs include leafy and conifer types, evergreens, and deciduous plants. They are used in parks and squares and to line boulevards and streets. In separate plantings, varieties with spreading crowns (oak, ash, or plane trees) or umbellate crowns (silk trees) are used. Plants with weeping crowns (weeping willow, weeping birch) serve to decorate bodies of water. In alpine terrain, on slopes, and on steep mountains, spreading plants are especially attractive (rock cotoneaster, mountain pine, juniper). To bring greenery to streets and form treelined boulevards, trees with pyramidal crowns (cypress, poplar), round crowns (false acacia, linden), or conical crowns (fir, spruce) are planted. Many treelike plants can be shaped in any way through pruning; these include the box, thuja, laurel, yew, hornbeam, hawthorn, elm, and privet. Creeping plants (ivy, clematis, grape, ampelopsis) serve as vertical vegetation on walls, terraces, and belvederes; they also decorate architectural constructions such as arbors, trellises, and columns. Besides the local species, exotic ones imported from other regions are quite common.
Ornamental perennials are herbaceous plants that live for more than two vegetative periods. This is the richest group of ornamental plants in terms of species, and it includes flowering plants, plants with ornamental leaves, and plants with ornamental fruits. Ornamental perennials are used widely in gardens, parks, and squares. In temperate climates perennials are subdivided into plants that winter outdoors and those that must be taken inside for the winter. The latter are kept as starting stock, tubers, and rhizomes in dry storage at a temperature of 5°C. Certain perennial plants of southern origins are used as annuals in more rigorous climates (including ageratum, petunia, scarlet sage, and nasturtium). Perennials are regrown in the spring from rhizomes, tubers, or bulbs through restorative buds. According to their ornamental features, they are classified into different types. Flowering types are distinguished by abundant blossoms, brilliant colors and shapes, doubleness of flowers, and the aroma of the blossom or mass of small blossoms gathered into a raceme. Ornamental foliage plants are classified according to leaf slits, color variegation, brilliance of hues, and evergreens. Other classifications are plants with beautitul, brightly colored fruits; plants that develop exquisite brooms or heads (the grains); compact plants that form a turfy cushion as they grow, and the lianas (creepers, climbers, or crawlers). Perennials are used to create ornamental arrangements in flower beds, partitions in pavements, lawns, meadows in parks, and sunny clearings. Sometimes perennials are planted as solitaries, with only a single variety of large, highly ornamental plant. Perennials are used as colorful ground covers in flower beds and borders; creepers are used for intricate structures such as belvederes, arbors, arches, and curtains of greenery. Many perennial blossoms can be used in bouquets. They grow in one spot for three to five years or longer and multiply by division, shoots, or seed plantings.
Biennials are flowering ornamental plants which in the first year of growth develop foliage and in the second year produce stems with flowers and fruits. After maturing, they die. This group sometimes includes some perennials that are cultivated as biennials. True biennials include the alpine forget-me-not, which is used in flower beds on open soil and also for cut flowers. The Canterbury bell is used in flower beds and in open soil; honesty, in dry bouquets; foxglove, in group plantings and for cut flowers; and the mallow or hollyhock, in group plantings and for cut flowers. Of the herbaceous perennials that are cultivated chiefly as biennials, the best known are pansies and sweet William, which are grown on open soil; hesperis, or dame’s violet, used for group plantings, cut flowers, and distillation; and daisies, used for planting in borders and flower beds and, in winter, for growing indoors in pots. Biennials multiply by seed plantings in hothouses or on open soil, and some send out shoots.
The general term “ornamental annuals” is used for ornamental plants that are raised from seeds in the course of a single growing season. Most annuals are plants that grow for only a single year, but biennials and perennials that blossom in one year but do not winter outside (heliotrope, snapdragon, fuchsia, and lobelia) are considered as ornamental annuals too. Annual plants produce groups of lovely blossoms, ornamental leaves (amaranth, ornamental cabbages, and castor-oil plants), dried flowers (everlastings), cover plants, vines, hanging plants, and bouquet flowers. In temperate climates, most annuals are planted in March or April in hothouses and greenhouses in order to lengthen their growing season or to encourage earlier flowering. Later they are transplanted outdoors. Many annuals are planted directly in soil outdoors. The annuals include certain asters, larkspurs, balsams, pot marigolds, stocks, poppies, nasturtiums, petunias, tobaccos, marigolds, morning glories, sweet peas, and mignonettes. They are used for flower beds, mixed borders, borders, boxes, hanging pots, and group plantings.
Ornamental grains are grain plants used in ornamental gardening for borders and group plantings and for making bouquets of live flowers as well as dried ones. For individual and group plantings by walks, high grains are used (reedy arundo, red eriantus, wild sugarcane, and pampas grass); for borders and group plantings, short grains are used (canary grass, fescue, hare’s-tail grass, and tall ryegrass); for walks, meadow grass, fescues, ryegrass, and bent are used.
Bulb ornamental plants are of the Liliaceae and Amaryllidaceae families and are cultivated in ornamental gardening: snowdrops, squills, tulips, narcissus, hyacinths, and lilies. Hyacinths, tulips, narcissus, and some other bulb types successfully multiply by forced planting, that is, in hothouses and rooms. Bulb culture is developed in southern parts of the USSR, such as the humid subtropical zone of the Black Sea shore and the southern shore of the Crimea. In open plantings in the central regions of the RSFSR, bulbs such as snowdrops, squills, and narcissus are used chiefly for decoration in perennial flower beds and borders. In the southern part of the USSR, bulbs winter outdoors without cover, whereas in the central regions some plants, such as hyacinths, are covered with peat or fallen leaves in the winter. Bulbs multiply mainly by tubers that appear on the old bulb or by squamules or outer divisions of the bulb. Often tuberous plants are considered as bulbous ornamental plants, since they are similarly cultivated and their underground organs are outwardly similar. They include gladiolus, saffron, and meadow saffron.
N. V. TSITSIN