58 College of Forestry 



(■i) Proper aeration of the soil. 



j^ext to a supply of water, a well aerated soil is the most 

 necessary condition for successful tree growth. Probably 

 more street trees in Manhattan die because of a deficiency 

 in respect to air and water than from any other cause. 



Where a tree is not planted in turf, the only way to insure 

 a proper aeration of the soil is by frequent cultivation of 

 the ground surface above the roots. All street trees planted 

 in gravel parkings or in tree pits with or without gratings 

 should receive such treatment at least every three or four 

 weeks during the growing season. In the case of gravel sur- 

 faced tree pits which are protected by a fence from traffic or 

 in the case of tree pits surfaced with brick laid upon a good 

 cushion of loose sand it is probably only necessary to culti- 

 vate two or three times a season. 



Where gratings are used they should be of a design which 

 permits of easy removal for frequent cultivation. The chief 

 value of the grating lies in its improvement of aeration 

 conditions by protecting the ground surface from becom- 

 ing compacted by traffic. Hence an immovable grating which 

 prevents frequent cultivation destroys its main reason for 

 existence. There are a number of gratings in Manhattan 

 which are thus largely worthless. The soil beneath a grat- 

 ing, because of the nearly continuous shade, will soon grow 

 sour and prevent proper aeration if not cultivated. 



(5) A supply of plant food. 



Sufficient food for a successful street tree will be largely 

 secured from good soil, and sufficient air and water without 

 fertilization, but where the soil supply is unusually limited 

 an annual application of fertilizer is advisable. Bone meal, 

 lime, well rotted manure, and various chemical fertilizers 

 rich in phosphates and nitrates may all be used with success. 

 Where gratings are used oats or clover may be planted in 

 early summer and dug under when four or five inches high, 

 or dead leaves may be piled under the gratings in the fall 

 and covered with a light dressing of well rotted manure and 

 the whole spaded under the following spring. In the use of 



