BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 189 



the winter. In addition to stable and green manure, if other fertilizer 

 seems desirable, we would suggest the application of tankage, or dried 

 blood and superphosphate, either of which supplies nitrogen and phos- 

 phoric acid in an available but not too soluble form. 



In fertilizing the walnut it is evident that comparatively large 

 quantities of material must be used to obtain any real effect. The idea 

 of applying a few pounds -per tree of any substance with the expecta- 

 tion of producing some specific effect upon the tree or nuts is absolutely 

 futile. With large trees we would advise not less than 50 to 100 pounds 

 per tree of high grade materials, composed largely of fairly available 

 nitrogen and phosphoric acid, if any real effect is to be obtained. 

 This we would apply during the winter or spring at the time of plow- 

 ing the grove. 



PRUNING. 



The pruning of the walnut tree in the orchard has not resolved 

 itself into any such systematic practice as is the case with most fruit 

 trees. In almost all of our present groves, in fact, no pruning at all 

 is done, save that most growers usually go through each winter with 

 an ax and cut off all the limbs which have come down upon the ground, 

 in order to facilitate cultivation. There is quite a common impression 

 that walnut trees should not be pruned any more than is absolutely 

 necessary and that cutting in the top results in injury of some sort or 

 other. One suggestive fact is evident with the walnut tree, however, 

 namely that as the trees grow older and their tops closer together the 

 setting of nuts through the interior of the tree declines very notice- 

 ably, and also that trees in outside rows or isolated trees which stand 

 out by themselves produce decidedly more heavily than those in the 

 interior of the orchard. This is especially noticeable in isolated door- 

 yard trees, which are almost invariably heavy producers. These obser- 

 vations have led some growers to take out some of the inside limbs 

 as the trees become older and more crowded, in order to maintain a 

 better exposure to the air and sunlight. Such a practice is in our 

 observation an excellent one and we would recommend in the case of 

 large, old trees with crowded tops that a considerable amount of wood 

 be taken out in the center of each tree in order to open them up. In 

 young trees little pruning is ordinarily necessary, except that in very 

 windy localities it may be necessary to keep pruning to some extent 

 on the side away from the wind in order to counteract the tendency 

 toward a one-sided growth. The walnut tree, except when influenced 

 by wind, has a very strong tendency toward symmetrical development, 

 regardless of the form in which it starts. If a large limb develops on 

 one side during one year's growth this growth usually drops back the 

 second year and the tree develops more rapidly on the other side, 



