ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 52 



Fig. 3. — The soil profile tube is a handy tool for removing cores of 

 soil from the upper 10-14 inches. Many properties of the soil can be ob- 

 served by examining such cores. 



These tests will help to determine if the phosphorus or potassium 

 content is low in the soil around shade trees. 



Diagnosing soil deficiencies by analyzing plant tissue cur- 

 rently serves as a good research tool but is not considered 

 practical for use in shade tree fertilization. 



Consider the disadvantages of fertilizing 



Although the advantages usually far outweigh the disad- 

 vantages, certain points should be kept in mind. Fertilizing 

 trees or shrubs in lawns will also stimulate grass growth, and 

 frequent mowing may be necessary. Unless regularly pruned, 

 small ornamental shrubs, through fertilization, may become too 

 large for their locations in a few years. Heavy nitrogen applica- 

 tions tend to increase twig growth and reduce flowering in some 

 ornamental shrubs. Some woody species may become tall, spindly, 

 or succulent and develop a weeping appearance after prolonged 

 fertilizing. 



American beech, white oak, and some crab apple varieties 

 have been reported injured by fertilizer formulations containing 

 nitrogen, phosphorus, and potassium. All fertilized plants should 

 be observed critically each year to determine the effect of 

 fertilization. 



WHEN SHOULD YOU FERTILIZE AND WITH WHAT? 



Time of application 



Nitrogen fertilizers should be applied annually. Little avail- 

 able nitrogen remains in the soil from year to year, since most of 



