18 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 52 



SUMMARY OF RECOMMENDATIONS 



Recommendations for shade tree fertilization should be 

 based on experimentation using known tree species and known 

 soil types. Only limited controlled experimentation on fertilizing 

 shade trees and shrubs has been accomplished. The recommen- 

 dations here are based primarily on the authors' own experi- 

 ments and on information gleaned wherever possible from ex- 

 periments in arboriculture, pomology, forestry, and agronomy 

 (see selected references). The recommendations should be con- 

 sidered as generalizations or guides. 



Fertilizing 



1. Measure accurately the area to be fertilized and deter- 

 mine its size in square feet. For ease in calculating size and ap- 

 plying fertilizers, a square or rectangular area is suggested. 



2. Weigh accurately the amount of fertilizer material to be 

 used. A bucket and kitchen scales are used by the authors 

 (Fig. 5). 



3. Apply nitrogen fertilizers annually to the soil surface at 

 the rate of 6 pounds of nitrogen per 1,000 square feet. This is 

 easily and uniformly accomplished with spreaders commonly used 

 to apply fertilizer to lawns. Nitrogen fertilizers are most effec- 

 tive when applied in April or early May before trees break dor- 

 mancy. To prevent grass burn, wash fertilizer off grass blades 

 immediately after application. 



4. Apply phosphorus and potassium fertilizers every 3-5 

 years. Phosphorus should be applied at the rate of 3.6 pounds of 

 phosphoric acid (P2O5) and potassium at 6 pounds of potash 

 (KjO) per 1,000 square feet. 



One method is to place dry fertilizer in a series of holes 

 12-15 inches deep at 2-foot intervals in parallel lines 2 feet apart 

 throughout the area to be fertilized. A second method of applying 

 phosphorus and potassium is to use water-soluble materials and 

 inject them into the soil using a hydraulic pump and a soil 

 needle. The injections are made 18 inches deep at 214-foot 

 intervals in parallel lines 214 feet apart throughout the area to 

 be fertilized. 



Phosphorus and potassium may be applied in the spring or 

 fall. They are often applied in the spring when hole preparation 

 or soil-needle injection is easiest. 



