Banks
Read about Banks in the Standard Cyclopedia of Horticulture
|
|---|
|
Banks. The means of holding and planting banks and steep surfaces is one of the perplexities of the horticulturist and landscape designer. The banks to be considered may be defined as very steep earth slopes with a bare, shifting surface, requiring protection and planting, or a surface covered with natural vegetation. Figs. 466-469. Low banks, either curved or rigidly formal, usually enter into symmetrical designs of the elaborately finished surroundings of a fine home. Usually they are placed to outline or to inclose parts of a design, or to decrease or increase the apparent height of a building or other structure, or of a garden compartment. Protection. One problem to be solved is the protection of sea, lake, river, and small stream banks and bluffs against the sliding of the soil, due to waves or along-shore currents in sea or lakes and to running water, especially floods, in stream beds. Such water-action, cutting under the base of a bank, causes the soil above to slide down. On lake and sea shores, jetties built from the bluff-base into the water will check an eroding marginal current, make it drop its load of silt, and extend the shore. In many positions willows, planted close together in a wide band on the beach or at the bluff- base, will accumulate and fill with roots the soil that is washed down and blown in, and thus create a water- resisting barrier. Along salt water, plantations of the sea-beach grass, Ammophila arenaria, and the shrubby Baccharis halimifolia and Ivafrutescens are serviceable; and far South, the mangrove may be planted on outermost sea-edges. Another bank trouble is soil-seepage water coming to the surface part way up the slope and making mud patches that slide down and cause the soil above to cave away. Usually this sloughing is at an impervious soil layer at some feet below the surface, to which the water passes, then finds its way out to the bank-face. If this water is at fixed spring-like points, a tile drain laid in porous material about 3 or 4 feet deep and directly down the bank to a concrete anchor at the outlet opening will usually take off the water that causes sliding. If the seepage is all along the face of the bank, it may be necessary to carry a drain some feet back from and parallel to the edge of the bluff-top down to and a little into the impervious soil, with tile outlets down the bank. The surface of banks is often gullied by water running from the top down the face at frequent intervals. This may be prevented by forming a ridge or barrier at the edge of the bluff to carry the water along sodded channels to paved or piped outlets down the slope. Sand-bluff surfaces that drift with the wind need thick plantations of plants that will grow well in sand, with a mulching of hay, leaves or litter to keep the sand in place until vegetation is established. The erosion of large streams at the base of bluffs is often beyond the means of individuals to control, although persistent willow-planting along shore and planting on the slope, will often suffice. In bad banks, a riprap of stone with plants having matted roots between the stones will hold. On smaller streams, ripraps of stones or stumps, while unattractive until covered with vines, will hold banks at critical places. A continuous stone wall is not a good barrier unless it is high enough on both sides to include flood-water, and the cost of such walls is too high for most individuals. On sliding slopes there is usually an overhanging upper edge with a short perpendicular edge just under it to be graded back. The material thus secured may be used at the foot of the bluff. When more ideal conditions are desired, the grading may be extended to give angular raw banks the graceful contours that nature's gradual rounding-down of angles will give. Planting. On low banks and terraces, where soil may be thoroughly prepared and well cared for, turf or any vigorous plant can be established. In elaborate garden designs, such planting is often trimmed or trained to a uniform surface or arranged to make a part of a formal pattern. On high banks, landscape beauty of distinction may be created by the selection, arrangement and management of artificial plantations or the natural growth. High banks uniformly drained and graded to prevent slipping, such as railroad and reservoir slopes, may be turfed. Such treatment is not recommended in large operations in which an interesting and varied surface- cover, or a low maintenance cost, is desired. When large bluffs require many thousand plants and limitations of cost require that they be planted with little soil preparation, varieties must be selected that will grow well in the soil presented. They must be plants that can be procured in large quantities at low cost, for the bulk of the planting, and it is desirable that they have such special characteristics as underground or surface stolons or trailing stems that root strongly at frequent intervals, or stems that root at the tips. There are also varieties with very densely matted fibrous roots that hold soil well. The following plants meet these requirements for the soils indicated: Low evergreen plants for the sandy or gravelly soil of the North: Bearberry (Arctostaphylos Uva-Ursii) an ideal evergreen trailing ground-cover for sand or gravel, of which collected plants must be used that are not easily transplanted. Trailing juniper (Juniperus communis). Savin juniper (Juniperus Sabina). These three species are not procurable in large quantities at low cost, and collected plants do not transplant readily. Low evergreen plants for good soil in shade: Evergreen spurge (Pachysandra terminalis), excellent for shade and hardy over a wide territory. Myrtle or large periwinkle (Vinca major), from Virginia south. Periwinkle (Vinca minor), from Pennsylvania north. The last three plants are offered by nurseries in large quantities, the latter at low cost by collectors, and collected plants transplant well. Japanese evergreen honeysuckle (Lonicera japonica). This climber and trailer is one of the best bank-covers in states south of New York, and it can be obtained in nurseries or from collectors in large quantities. Spring planting should be done very early. For low deciduous trailers or medium high shrubs for nearly all soils, the tip-rooting species of blackberry, such as Rubus canadensis, R. dumetorum, R. occidentalis, and the species with underground stolons, such as the cultivated high-bush blackberries, and red raspberries, are serviceable and can be obtained in large quantities at low cost. Plants having a similar habit may also be thus secured, as the matrimony vine, the Indian currant, the weeping golden bell (Forsythia suspensa), the wild roses, (Rosa lucida or R. nitida), the staghorn sumac (Rhus typhina). Of low-cost trees, the common locust, soft maple, box elder, and Russian mulberry, are all suitable. Of matted-root plants, the Japanese barberry, the hop-tree (Ptelea trifoliata), the European euonymus, the common buckthorn, can usually be readily procured. Of small trees for shade, the flowering dogwood and red-bud are especially suitable and attractive from Massachusetts and New York south. Of tall evergreen trees, the white pine is more serviceable for light soils and more easily procured; the arborvitae and red cedar are the most available medium- height trees for average soils. In California, the mesembryanthemums are largely used for bank-covers. It is very desirable to establish a ground-cover of low shrubs and especially herbs under trees on banks as soon as practicable. By using hay containing wild asters, thoroughworts, blazing star, goldenrod, perennial sunflowers, and the like, for mulching young plantations, many of these plants will be introduced from seed, especially when seeds are mature. These will gradually be superseded by such shade-loving plants as ferns, violets, woodland asters, and goldenrods, especially if colonies of these plants are introduced as soon as the plantations are high enough to give shade. Arrangement. If it is important to retain an extended open view from the top of high banks, then high trees must be confined to the lower edge, medium-sized trees and large shrubs to the central zone, and trailing plants or low shrubs to the upper zone. If the bank is a low one, then low trees or large shrubs must be substituted for the large trees at the bottom of the bank. It is often more interesting, however, to allow the bank to be covered with tall trees and then open vistas and views through these trees by cutting branches and thinning out as they develop. Banks offer rather an unusual opportunity for the development of interesting detail in the development of the planting, because of varying conditions of moisture and soil. Such interesting details should be made accessible by trails following along the slope on easy grades that can be made at the time the bank is first graded or at later periods as the growth develops.
|
