138 FOOD FOR PLANTS 



or August, according to climatic conditions, when a 

 cover crop may be sown. Alfalfa, one of the clovers, 

 vetch, cowpeas, soy beans, rye, oats, buckwheat and 

 other crops are used as covers. A leguminous crop 

 is usually considered preferable. 



Pruning. 



Only a bare outline of the principles of pruning 

 apples may be given here. The purposes of pruning, 

 briefly are: 



1 . To preserve the proper balance between top and 

 root system at the time of setting out. 



2. To prune to the best size and shape. 



3. To remove all dead, diseased, and injured wood. 



4. To make the top open in order to admit sun- 

 light. 



5. To regulate the number of limbs composing 

 the top. 



6. To fix the branches at the proper height above 

 the ground. 



7. To do away with a weak crotch and crossing 

 or interfering branches. 



8. To promote the right amount of wood growth. 



9. To regulate the number and the distribution of 

 wood and fruit-bearing buds. 



Several types of pruning are practiced. The Cen- 

 tral Leader type provides a strong upright central 

 limb with side branches, uniformly distributed about 

 it. The Open Center type has no central leader, but 

 usually two to four main branches joining the trunk 

 at the crotch, and giving a vase-shaped top. The 

 Double Headed type comprises three chief parts: 



