KEEPING SHADE TREES HEALTHY 



CURTIS MAY 



The formula for keeping shade trees 

 healthy has three parts: Selecting 

 kinds of trees that are adapted to your 

 locality; planting them in good soil; 

 and following a program of soil main- 

 tenance, watering, pruning, and treat- 

 ment for diseases and insects. 



The kinds of shade trees that will 

 grow well in the different regions are 

 discussed in preceding articles. A few 

 general considerations need to be re- 

 peated here: Generally speaking, the 

 species that grow naturally in any 

 region are adapted to the climate of 

 the region and can cope with native 

 pests. If they also can withstand the 

 artificial conditions imposed when 

 they are planted for shade trees, it is 

 advisable to use them, provided they 

 are of the proper form and size. Some 

 trees grow satisfactorily outside their 

 natural range, it is true, and many 

 species introduced from other con- 

 tinents succeed well in various parts of 

 the United States. Before one makes 

 extensive plantings of the introduced 

 species, he will do well to check their 

 usefulness, hardiness, and values. On 

 those points, other sections of this 

 book, aboretums, experiment stations, 

 nurserymen, and garden publications 

 give a wealth of information. 



Your properly chosen tree has been 

 planted how does it grow? 



If it grows well, leave it alone. If 

 it does poorly, one or several remedies 

 may be needed. Some of the symptoms 

 of disease and decline in trees are so 

 specific that the cause can be diag- 

 nosed accurately and easily. Other 

 symptoms can develop from a number 

 of causes. Five early warnings that all 

 is not well are sparse foliage; leaves 

 that are paler green than normal ; die- 

 back of the tips of the twigs; drying 

 and loosening of the bark; and ab- 

 normally slow growth. 



Look first to the soil its fertility, 

 drainage, aeration, and moisture. The 



trouble might be that the roots are not 

 developing as they should because the 

 soil is heavy clay, airless and poorly 

 drained, such as the soil often is that is 

 excavated in the construction of a base- 

 ment. If so, fertilizer, organic matter, 

 and loosening of the soil are needed. 

 Most of the roots of trees do not 

 grow deeply into the earth. Unless the 

 soil is gravelly or sandy, the bulk of 

 the roots of most kinds of trees is likely 

 to be found in the upper 3 feet; com- 

 monly they penetrate even less deeply. 

 When the minerals in the soil mass in 

 which the roots are growing become 

 inadequate to maintain good growth, 

 the tree begins to show signs of decline. 

 Annual depletion of the mineral ele- 

 ments by taking away all grass clip- 

 pings and fallen leaves may not affect 

 the tree for several decades of its early 

 life, but after 30 to 50 years signs of 

 mineral depletion often are evident. 

 Street trees are even more likely to 

 decline from lack of soil fertility than 

 lawn trees, because the soil mass in 

 which their roots can develop well is 

 likely to be even more restricted than it 

 is for lawn trees. The need for addi- 

 tional minerals in the soil can be cor- 

 rected by applications of fertilizer. 



THE FERTILIZER should be applied 

 regularly, preferably in the spring, just 

 about the time growth begins. It can 

 be applied safely until about the mid- 

 dle of the summer in most parts of the 

 country even later in the Deep 

 South. Or, the fertilizer can be put on 

 in the fall after the trees have lost 

 their leaves. Evergreens, however, 

 should not be fertilized in the late fall. 



The amount of fertilizer to be used 

 without danger of causing injury varies 

 somewhat with the kind of tree, the 

 condition of the soil, and the time of 

 application. A safe dosage is 2 pounds 

 for each inch in diameter of the trunk 

 3 feet above the ground line. Wherever 



