|Standard Cyclopedia of Horticulture|
Drainage. Underground or sub-drains serve to relieve the land of free water, which is harmful to most plants if left to stagnate in the surface soil or subsoil. They serve not only to dry the land in early spring, but indirectly to warm it, for if the water is removed the sun's heat warms the soil instead of cooling it by evaporating the surplus water. Tenacious lands devoted to gardening and small-fruits are made more productive, warmer and earlier by sub-drainage. Drains promote nitrification, assist in liberating mineral plant- food and cheapen tillage. They serve not only to remove deleterious stagnant water, but they promote aeration as well, and this hastens beneficial chemical changes in the soil. Drainage promotes the vigor, healthfulness and fruitfulness of plants. Tenacious soils are made more friable by drains, thereby giving as easier access to plant roots, while the percolation through the soil of rainwater, which carries some plant- food, is hastened. Rain-water in the spring is warmer than the soil; in midsummer it is cooler than the soil: therefore, percolation of rain-water warms the soil in the spring and cools it in extremely hot weather. Drains serve not only to relieve land of free water, but they impart to it power to hold additional available moisture, which materially benefits plants during droughts.
Drainage is of two kinds, surface and sub-drainage. On land on which large outlays of money are to be expended, as in horticultural plantations, it is of the utmost importance that the soil be freed to considerable depths from stagnant water. Trees, many shrubs, and even some garden crops send their roots deeper into the subsoil than most of the cereals, hence they require a greater depth of drained feeding-ground. In horticulture the planting may often precede the harvest by five to ten years, while with many farm crops the harvest follows the planting in a few months. If the grain-raiser loses one crop, an annual, by planting on wet land, the loss is not great, but if the orchardist loses fifteen to twenty years of labor by planting on undrained lands, before the mistake is discovered, the losses are serious. Some lands require little more than to be relieved from surplus surface water in early spring. This may be accomplished by forming ridges and open furrows as far asunder as the rows of trees are to be placed. But it is only rarely that surface drainage fully prevents serious damage from surplus moisture. Surface drainage may be considered a cheap way of temporarily alleviating undesirable conditions. It does not always eradicate them. Fig. 1347 illustrates how sub-drainage lowers the water-table (or the area of standing water), and thereby ameliorates the soil.
Sub-drainage consists in placing conduits of tile or other material in the ground at depths varying from 2 to 4 feet, and at such distances apart as will serve to relieve the subsoil of deleterious stagnant water. When suitable stones are at hand, they are sometimes used instead of tile for forming drainage conduits. If such use is made of them, the drains should be somewhat deeper than tile drains, since the stones which form the drain occupy nearly a foot of the depth of the ditch and are more likely to become obstructed, especially if placed near the surface, than are tile drains. The throats or openings of stone drains are irregular in size, while those of tile drains are smooth and uniform in size, and are, therefore, most desirable. Years ago, various flat-bottomed tiles (Fig. 1348) were employed, but the style in general use at present is the cylindrical unglazed tile shown in Fig. 1349. They should be hard-burned. Because of the low cost of cement, tiles made of sand and hydraulic cement have recently come into use; they require no burning, are stronger than tiles made of clay and are just as efficient, except in alkali and where frost penetrates very deep.
In semi-arid districts in which irrigation is practised, if there is a hardpan, nearly or quite impervious to water, located within 3½ to 4½ feet of the surface, the land will in time become sour or charged with injurious alkaline salts, and in many cases ruinously unproductive. Lands of this description are, for the most part, situated west of the 100th meridian. A striking illustration of raising the water-table by too liberal irrigation may be found in a tract of several thousand acres in Tulare County, California, which formerly produced grapes and peaches abundantly but now yields nothing except a little hardy forage. The water table in this region was once 30 to 40 feet below the surface, but as a result of constant irrigation has risen to within 2 or 3 feet and, in low places, even to the surface, forming a sort of tule swamp. Since the water-table could not be lowered enough to restore the land by under drainage, for lack of an outlet within reasonable distance, it is probable that the only way to reclaim it would be to sink a well and pump the surplus water into a surface ditch. Irrigation with pure water would then sweeten the soil and render it again productive; and the whole process of restoration need not be excessively expensive.
If the hardpan is less than 2 feet in thickness, the land may be improved greatly for orchard and vineyard purposes by the use of dynamite. Blasting should be deep enough to allow the surplus water to escape into the porous earth or gravelly soil beneath the hardpan. On the Pacific coast this method of draining orchard and vineyard land has been quite successful. In any case, unless the soil has good natural sub-drainage, it is both wise and economical to blast out holes for trees and vines; for the cost of digging holes, if they are as large and deep as they should be, is lessened by an amount almost equal to the cost of blasting.
Recently, powerful tractors have solved, to some extent, the problem of drainage in many cases by making deep plowing possible before planting and during the first few years of subsequent tillage of the orchard or vineyard. This machine with the tillage implement turns easily at the ends of the field within the space allowed for turning a span of horses and a plow; it can pass under limbs where a 14-hand horse (56-inch) can pass, and as close to the plants as a span of horses can. It furnishes also power and locomoton for spraying and for opening trenches to a considerable depth (18 to 44 inches) for the reception of drain-tile.
In some regions, drains are placed 200 to 300 feet apart, and serve their purpose well. In others they should not be placed farther apart than 20 to 30 feet. Wherever the subsoil is composed of tenacious fine clay, through which the water moves upward or downward with difficulty, the narrower intervals are necessary. In some instances the surplus water in the subsoil is under pressure by reason of water which finds its way into it from higher levels, and if this is not removed, the water has a constant tendency to rise to the surface. In many such cases drains placed at wide intervals may serve to relieve the pressure and drain the land. Since sub-drains are designed to be permanent, are expensive to construct and difficult to repair, the principles of drainage should be well understood, and the work should be undertaken only after a most careful inspection of the land and after the fundamental principles of the subject have been mastered.
Mains and sub-mains should be avoided so far as possible, since they greatly increase cost, tend to become obstructed, and are often unnecessary. The three long mains in Fig 1350 are not drains, strictly speaking, since the land may be as fully drained without them, as shown in Fig. 1351; therefore, they serve only to conduct the water of the drains proper. Tiles of 3 to 4 and 5 inches diameter should be used when the drains are infrequent and the flow of water considerable. Smaller ones, 2 to 3 inches in diameter, will suffice when the intervals between the drains are narrow.
Drains should have as uniform a fall as possible, and no abrupt lateral curves or sharp angles should occur as are seen in many places in Fig. 1350. If the drain has a rapid fall in its upper reaches, as is often the case, and but slight fall in the lower, a silt basin should be constructed at the point at which the rapid changes into the slight fall, if obstructing silt is present. All drains which may be necessary should be placed before the planting occurs. Orchard lands may be drained in the spring, fallowed in the summer, and planted in the fall or the following spring. Drains placed at frequent intervals because of the tenacity of the soil should be comparatively shallow, for if placed deep or at wide intervals, the water will be too long reaching them. If drains are placed at wide intervals they should be at least 3½ feet deep to be most efficient. If the parallel system is adopted (Fig. 1351), there may be more outlets to construct and maintain than is desirable; if so, the system might be modified by constructing a sub- main, one side of which will serve also as a drain, and but one outlet will be required (Fig. 1352).- Drains through which water runs for the greater part of the year are likely to become obstructed by roots, if water- loving trees, such as the willow, soft maple, and elm, are allowed to grow near them. If floating silt is present, the joints of the tiles should be protected for two- thirds of their upper circumferences by a narrow strip of tarred building paper (Fig. 1353), or collars should be used. Stone drams should receive a liberal covering of straw or some similar material before they are filled. I. P. Roberts.
Drainage for landscape work.
The value of a thorough knowledge of the possibilities of drainage in landscape work has been overlooked until recent years as a definite field entirely apart from general drainage for agricultural purposes.
Drainage under the headings of this article is installed with the following objects in view: 1. Maintaining well-drained areas for firm lawn surfaces. 2. Maintaining well-drained and firm surface conditions for recreation areas. 3. Draining of surface water and ground water from roads. 4. Draining foundations for walks. 5. Preserving the normal soil conditions for newly planted trees. 6. Draining swamp and marsh areas to prevent breeding of mosquitos.
1. Drainage far lawns.
The secret of a perfect lawn is attributed to drainage conditions which provide a well-drained subsoil and a firm surface that may be readily freed from any excess water during heavy rains. The installation of drainage for this purpose is required only in the more compact soils that do not drain naturally. Sandy soils seldom require artificial drainage unless immediately underlaid with a stratum of impervious clay. On any lawn the topography of which does not permit the ready surface run-off and the subsoil of which is compact clay, the necessity of installing sub-surface drainage is strongest.
A drainage system for providing ideal soil conditions for perfect lawns must be installed carefully. Four- inch tile, is often used in the lateral systems while either 6-inch vitrified pipe, or the No. 2 quality of 6- inch round tile, is used for the main lines. All drains should be laid on an even grade of not less than ⅛ of an inch fall to each linear foot of drain, and preferably not less than ¼ of an inch fall for each foot of drain. If perfect drainage is desired, the distance apart of these drains should not exceed 20 feet. In accordance with the general laws of drainage, tile should be laid at a more shallow depth in the heavy soils than in the lighter soils, and should be spaced at closer intervals than 20 feet, this space varying largely with the desire to free the lawn immediately of any excess surface water.
In all tile drainage whether for lawns or other purposes, a space of approximately ⅛ inch should be allowed between the ends of the pipes. The covering of tar paper and cinders should be placed over each joint as shown in Fig. 1353. The tile should be placed on a firm bottom of clay or other natural soil, and surrounded on all sides, and covered to a depth of not less than 6 inches with cinders, crushed stone, or washed gravel (Fig. 1354). In very heavy clay, the trench excavated for the tile should be filled with cinders, crushed stone or gravel to a line separating the looser top soil from the clay subsoil (Fig. 1355). In heavy soil and for perfect lawn drainage, the lines of tile ought not to be laid deeper than 2½ feet and the cinder fill should not be less than 15 inches in depth. In the lighter sandy loam soils, the tile may be laid to a depth of 3 to 3½ feet.
It is often found necessary when lawns are constructed on sandy soil to prevent excessive drainage, rather than to encourage drainage conditions. In these extreme sandy soils, the surface water seeps away so readily that the lawns become exceedingly dry during the warm and dry months. To prevent this condition a layer of clay 4 inches deep should be distributed over the sandy sub-grade prepared for the lawn, at a depth varying between 10 and 18 inches below the proposed finished surface of the lawn. This clay is thoroughly compacted and serves as a partial barrier against abnormal seepage which would otherwise occur, and thereby retains the moisture necessary for the capillary attraction to feed the roots of the lawn grasses.
2. Recreation areas.
Areas naturally falling under this heading are tennis-courts (clay and turf), bowling-greens, clock- golf areas, and croquet-lawns. All of these require a more careful study of drainage conditions than is given to the average lawn. It is essential that such areas be so completely drained that the surface condition is always firm, even after the average continuous heavy rains.
Tennis-courts.—These areas require the most careful study of drainage conditions. The average tennis- court requires two types of drainage,—surface and sub-surface. Surface drainage is cared for in two ways, (1) either by giving the court a gradual slope to one end, or (2) as shown in Fig. 1356, where the surface of the court is sloped from either end toward the middle line. This method, shown in Fig. 1357, gives probably the most satisfactory results, because, in this way, if surface conditions at the middle of the court are correct, the surface water is cared for most readily and with the shortest possible run-off. This drain across the middle of the court may be either an open concrete drain with a plank laid over the top and flush with the surface of the court, or a blind drain filled with a coarser crushed stone and fine crushed stone, over which is spread a thin layer of washed sand. The bottom of the drain ought to be approximately 6 inches lower, at the point where the outlet to the sub-drain is located, than the elevation at the extreme high points of the drain. The method of establishing these grades varies largely with the requirements of this particular problem. The water, as it reaches the low point in the drain, is conducted at once into the main 6-inch drain, which also takes ground-water from the underground system of drains. When the court is so constructed that one end is lower than the other, in order to assist surface-drainage conditions the courts should be level from side to side. Fig. 1357 shows the general distribution of the system of tile to care for the sub-surface water in tennis- court construction. This would apply equally well to the construction of other recreation areas, including clock-golf-greens, bowling-greens and croquet-lawns. In the construction of all tennis-courts, the trenches excavated for the tile should be filled with cinders or an equally porous material to a height not less than 6 inches below the proposed finished grade of the court.
Clock-golf-greens, bowling-greens, and croquet-lawns. — A thorough distribution of tile drains installed as outlined below, should meet all the requirements commonly imposed from the drainage standpoint upon the construction of these recreation areas. Lines of 4-inch tile should be placed, at intervals of not more than 10 feet. For the most thorough and ideal drainage of these areas, provided the cost is not prohibitive, the construction would be as follows: A neat sub-grade should be made at a depth not exceeding 15 to 18 inches below the proposed finished surface of the recreation area. The necessary lines of tile should be laid in trenches at a depth varying between 2 and 2½ feet below the finished grade, these trenches to be filled with cinders, crushed stone or gravel (Fig. 1355). On this sub-grade, thus completed, the entire recreation area should be filled to a point approximately 6 inches below the proposed finished grade, with cinders, or some equally porous material. On this finished surface, the remaining 6 inches should be filled with a layer of loam free from clay, but composed of a small percentage of sand. In this way, a firm surface will be obtained which will readily care for any surface and subsoil water.
The secret of a perfect road surface lies (1) in the proper crown of the road, and (2) in the adequate drainage of the subsoil or foundation. The first provision cares for the surface water, and the second provision eliminates any surplus ground-water.
On all private estates on which roads are constructed on heavy clay soils and not on grades greater than 4 per cent, the secret of success depends upon drainage installed in either of the two ways shown in Fig. 1358 or Fig. 1359. Installing a line of drains under the middle of the road is used in soils in which the ground- water level is abnormally high. Such drains should range in depth from 2 to 3½ feet below the finished surface of the road, and the trenches should be filled with a porous material and not with the natural soil. The method of installing drainage under the sides of the road, as shown in Fig. 1358 is used in heavy clay soils, and serves to keep the foundation of the road on well- drained soil. These drains are installed at a depth varying from 2 to 3 feet in trenches filled with cinders or equally porous material.
Turf pleasure roads, so frequently constructed on private estates, should be thoroughly drained with a line of tile placed under the middle of the road, unless the road is constructed on a heavy foundation of field- stone or gravel which forms a natural drain path for surface-water and soil-water.
In providing drainage along the sides of roads constructed on clay soils through virgin woods, it is sometimes necessary to carry these drainage lines a considerable distance through the woods to suitable outlet points. The joints of all such lines of drainage should be cemented, otherwise the artificial conditions produced by the increased drainage will work serious injury to many large trees growing on either side. In general it is very unsafe to install drainage lines through virgin woods, without this precaution. Roads constructed through such woods would better be drained by laying a line of tile under the middle of the road as shown in Fig. 1359.
A most frequent method of providing drainage for walks is that shown in Fig. 1359. A line of 4-inch tile is laid at a depth varying between 18 inches and 30 inches below the finished grade of the walk and following the middle line of the walk. The trench for the tile is filled with a porous material to a height even with the bottom of the cinders used for the foundation of the walk, or laid as shown in Fig. 1359.
5. Newly planted trees.
All trees planted in clay soil require drainage. If the pockets in which such trees are planted are not thoroughly drained, the area excavated and re-filled with soil when the trees are planted becomes a pocket for ground-water. This pocket or reservoir collects the water, which, if not carried off by means of drains, will very likely cause the death of the trees. All large trees, especially those which do not grow best with their roots in the water, must be provided with drainage. The common method of drainage is to install a line of 4-inch tile leading from the bottom of the excavated hole to a main line of tile which may have been installed for other drainage purposes, or to the nearest outlet if no such line exists.
6. Drainage to prevent mosquito-breeding.
It is a frequent practice, especially on large estates, to install open ditches from 50 to 100 feet apart in swamps and in salt marshes, in order to provide a means for draining such areas, and thus preventing the presence of stagnant water, which is conducive to the breeding of mosquitos. These trenches are excavated at depths varying from 2 to 3½ feet. The more frequent the trenches, the shallower they may be made and still provide adequate drainage.
The foregoing article pertains only to the particular phases of drainage especially to be considered in connection with landscape work. For additional information on the general details concerned with drainage, refer to the main article upon drainage, p. 1072. A. D. Taylor. Drainage and watering for newly transplanted trees.
Drainage is an essential in all retentive soils and is a safeguard even on sandy gravelly subsoils against overwatering. Drainage is likely to be vetoed on the score of expense or on the excuse that the subsoil is gravelly; whereas, there are only gravel stones in hard- pan which holds water. A dram made by filling a pit with stones is frequently inadequate as it fills with water, which backs up into the hole, saturates the soil around the roots and rots them. Rotting of only a part of the roots may injure the tree more than the cutting off of that amount of roots.
The soil in which to plant should be open, porous and aerated. Soil which has been piled up as in grading operations is likely to be sour from the decay of the sod and from the packing by teams and scraper. Muck from ponds which has been piled and mixed with lime for a year may still be sour. Clay soil packed by the water and packing-sticks may remain too compact and .not aerated enough, may be too much saturated with water and, therefore, rot the roots. Manure should not be mixed in the soil around the roots on account of the danger of souring and rotting the roots. This rotting is determined by digging down to the roots and finding them of blue-black color with a sour smell. Sometimes this decay has not reached through the bark of the roots and other times it has penetrated the bark and turned the cambium blue-black. Sour soil is likely to be of bluish or greenish color rather than chocolate-brown, and have a sour smell like that underneath a manure heap. The smell is most readily detected by breaking open a lump of soil. In digging into sour soil and soil that is over-saturated, the spade makes a peculiar sucking noise as in digging in a bog. If at the time of examination the soil is already become sour, it is best to take out this sour soil and put in fresh soil covering the roots only 4 inches. The ball of earth in the center will not be so liable to get sour because it has not been disturbed. As brought out by Stringfellow in the "New Horticulture," soil that is dug over will take in water and become saturated; whereas, soil that has not been disturbed will retain air in the soil-spaces even if submerged. The ball of earth is also prevented from becoming saturated by the undisturbed feeding-roots which absorb the moisture.
Watering cannot be by rule, but must depend on examination of both ball of earth in the center and the outer roots. The difficulty will be to keep the ball of earth sufficiently damp on account of the rapid withdrawing of moisture by the roots. The danger will be that the soil outside the ball of earth will take up the water too rapidly, remain saturated several days and rot the roots. Examination is best done by shovel and fork, digging down 1½ feet both in the ball and outside. An easier way is to bore into the soil with an auger. It will usually be found that the central ball of earth is dry and dusty in the summer even if the surface and outer soil is damp. The growth of weeds and grass will indicate the same. A good way to water is to make a basin around the width of the ball of earth, fill it with water 6 inches deep, make crowbar holes into the ball for it to soak in. Many mistakes are made in overwatering— letting the hose run all night or watering every day, thereby rotting the roots.
Mulching is frequently neglected, the tree starving for lack of humus. A close cut lawn around a newly planted tree may be the ideal of neatness, but it means starvation and thirst for the tree and is the principal cause of slow growth over several years, making new, bare and ugly landscapes. The mulch should extend as wide as the roots and be from 3 to 6 inches deep, of strawy manure, leaves, grass, salt hay or similar organic matter. Too much manure may sour the soil and rot the roots, if it lies heavy and compact and keeps out the air. Light strawy manure is better. If the mulch blows about and is untidy, it may be kept in position by wire netting, earth, or the planting of small shrubs.