258 Landscape Gardening 



nant water which is so injurious to plants and so productive 

 of discomfort; it also has the direct effect of making the soil 

 warmer and admitting air and gases freely. The tempera- 

 ture of ground that is saturated with water can never be 

 greatly increased, by whatever power of sun it may be acted 

 upon, nor can air circulate properly through a hquid medium. 

 Warmth and air to the roots being essential to the healthy 

 growth and fertility of plants, drainage becomes of the highest 

 consequence in soils that are naturally wet. 



Underdraining is now generally admitted to be the only 

 effectual mode for any description of land, but this is espe- 

 cially the case with garden ground. The roots of many vege- 

 tables, and most trees and shrubs, strike down so far into 

 the earth that shallow drains would be continually in the 

 way of their progress, and would be very liable to be choked 

 or injured by them. The more close, hard, and retentive the 

 subsoil may be, moreover, the stronger will be the necessity 

 for deep drains. Still, any extravagant depth need never be 

 attempted. Three feet six inches to four feet below the ordi- 

 nary surface will in general be the utmost depth required 

 for common drains, while main drains should be two or three 

 inches deeper. Where the substratum is only sandy, three 

 feet for the ordinary drains will usually be enough. They 

 can be about three inches wide at the bottom and fourteen 

 or sixteen inches, or just enough to admit the draining tool 

 conveniently, at the top, keeping the main drains one or two 

 inches wider at the bottom in accordance with the size of 

 the tiles to be employed. Common drains in gardens may 

 be in parallel lines of not more than five yards apart and 

 nearer if the soil be very heavy. 



Tiles or pipes are the materials most frequently chosen for 

 draining land, though they are certainly not the best for 

 gardens or where trees have to be planted. They are very 



