56 College of Forestry 



The problems which have to do with soil conditions are 

 less simple of solution and yet it is upon the skill shown in 

 solving them that the success or failure of the whole opera- 

 tion must depend. To secure correct soil conditions it is 

 necessary to provide for each and every tree as follows: 



(1) A sufficient amount of good soil. 



In some cities no consideration has to be given to this 

 matter as the existing soil is satisfactory both as regards 

 quality and amount. In Manhattan this is practically never 

 the case, and generally speaking we must figure on providing 

 at least two cubic yards of first-class loam or topsoil and this 

 even when there is a subsoil of some value. When, as in 

 the case of the restricted tree pit, we must provide the entire 

 soil supply of the roots the minimum requirement should be 

 three cubic yards, while five would be better. In Paris three 

 cubic yards of good soil is the standard requirement in 

 planting new trees. 



(2) Sufficient moisture. 



In the writer's opinion this is the most important element 

 in successful tree growth. In the case of trees planted in 

 very restricted areas this can only be supplied by artificial 

 means. Even where a good subsoil exists, it is doubtful if 

 the tree can secure, unaided, sufficient moisture for its needs 

 even after being established. The reason for this is that the 

 continuous pavement of the ground surface prevents the 

 ground water from being replenished from natural sources. 

 To secure successful street trees in Manhattan, continuous 

 irrigation is advised in practically all cases. There are 

 various ways of providing this, such as by tile and dry 

 wells, or by some form of underground pipes as in the so- 

 called " automatic " lawn sprinkling systems in use in the 

 arid regions of the southwest.* 



A method of irrigation advocated by some authorities is 

 to pierce the gutter curb opposite the tree and secure in this 



* Discussed in detail by the writer in the American City Magazine, 

 September, 1014. 



