FERTILIZING AND WATERING TREES 9 



it is used by plants or carried away by water. Nitrogen fertilizers 

 are most efficiently utilized by trees when applied in April or 

 May. However, applications in October or November will also 

 stimulate growth the following year. 



Phosphorus and potassium fertilizers are chemically bound 

 in the soil and become available slowly throughout several grow- 

 ing seasons. They should be added to the soil every 3-5 years in 

 either spring or fall, whichever is more convenient. 



Rate of application 



To fertilize trees and shrubs, fertilizer should be distributed 

 throughout the area where roots are most likely to occur. 

 Nutrient-absorbing roots of woody plants usually occur in the 

 soil area covered by the branch spread. However, trees that have 

 narrow tops or crowns, such as some poplars and columnar ma- 

 ples, have roots that extend w r ell beyond the branch spread. 



The amount of fertilizer to be applied should be based on the 

 area of soil to be treated and not on the diameter of the tree 

 trunk. When a square or rectangular area is fertilized, it is easy 

 to calculate the area involved. Also it simplifies uniform distri- 

 bution of fertilizer around each tree. Four stakes should be 

 placed in the ground to designate the corners of the area. The 

 stakes should be located so that the entire branch spread of the 

 tree will be included in the area to be fertilized (Fig. 4). The 



Fig. 4. — Stakes have been placed at the four corners of the area being 

 fertilized. They are far enough from the tree so that its entire branch 

 spread is included. 



