Illinois Natural History Siirvev Circular 56 



Should you fertilize? 



A number of factors should be considered before fertilizing 

 trees. Annual growth and leaf color can indicate nutritional 

 deficiencies. H trees have poor growth or pale green leaves, 

 fertilizer may make them grow faster and give their leaves 

 a darker green color. If trees are subject to attack by 

 canker-causing fungi or borers, fertilizer makes them more 

 vigorous and less subject to these attacks. The condition of 

 the soil also affects the fertilizer needs of trees. 



Rate of annual growth 



The annual shoot growth of a tree can be easily determined 

 on species with terminal bud scale scars. Bud scales enclose 

 and protect buds on the ends of twigs during the winter and 

 leave scars that encircle the twig after the scales fall in the 

 spring. These scars remain evident for several years on many 

 tree species. 



The distance from the dp of the branch to the ring of bud 

 scale scars nearest the tip is the current season's growth. The 

 growth of previous years can be determined by observing 

 the distance from bud scale scars to bud scale scars as they 

 occur down the twig (Figure 1 ). By observing the length of 

 growth for the preceding 3 or 4 years on several twigs, you 

 can estimate whether the growth rate was satisfactory or 

 unsadsfactory, increasing, decreasing, or stable, and suitable 

 for the species. 



Growth rates among tree species vary and the growth rate 

 of a given tree is in turn affected by its age. Soil types, the 

 spacing of trees, and other environmental conditions also 

 affect rate of growth. As a general guide, terminal twig 

 growth on most trees should be 9-1 2 inches or more a year. 

 Trees approaching mature size may grow only 6-9 inches 

 a year. 



A second method of determining growth rate in many tree 

 species is to measure the width of annual wood rings 

 produced in the trunk. This measurement is taken with most 



