BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 179 



way, however, have proven to be short lived and more subject to disease, 

 and nothing has been more positively demonstrated by experience than 

 the desirability of heavy soil for the walnut. The quality of the subsoil 

 is of particular importance since the roots of the walnut go down fairly 

 deep. A strong or heavy (though not wet or impervious) subsoil is 

 absolutely essential. 



A uniform and abundant supply of soil moisture is necessary, although 

 the tree is considerably resistant to drouth, especially when grown on 

 proper roots. Walnuts are frequently grown in California without irri- 

 gation even in the southern part of the State, but unless planted upon 

 soil of exceptionally good water-retaining capacity more or less irriga- 

 tion is almost always beneficial and profitable. In many cases where the 

 trees survive and do fairly well without water they would grow much 

 more rapidly, come into bearing sooner and bear much larger crops if 

 supplied with water. Too great an amount of moisture in the soil with 

 water constantly standing near the surface is very unfavorable to wal- 

 nut culture and the trees will not long withstand conditions of this sort. 

 Some latitude can be obtained in this respect by the use of a root best 

 adapted to excessive moisture, but it is hazardous to attempt walnut 

 culture on land where the water level stands within less than eight feet 

 of the surface or where it is likely to rise after the trees are planted. 



DISTANCE OF PLANTING, 



In practically all the older walnut groves in the State the trees were 

 planted too near together. The walnut tree is one which continues 

 growth for many years, making a large, spreading top } so that the trees 

 very soon come together unless planted a long distance apart. Further- 

 more, the production of nuts seems to be particularly favored by exposure 

 to the light and open air on all sides of the tree. The mistake of plant- 

 ing the trees too close together should therefore be carefully guarded 

 against. With vigorous growing varieties on good soil 60 feet apart is 

 none too much, and less than 50 feet should not be considered in any 

 case. Sixty by sixty feet gives about 12 trees per acre, 50 by 50, 17 

 trees per acre and 40 by 40, 27 trees per acre, when planted in squares. 

 By alternating the rows these numbers are slightly incrpased. 



Inter planting. With trees planted at these wide intervals and also, 

 somewhat slow in coming into bearing as compared with many fruit 

 trees, it becomes quite desirable when planting walnuts to interplant 

 with some other tree or crop in order to get something off the land while 

 the walnuts are coming into bearing. Fortunately, this is not especially 

 objectionable, as the walnut is a deep rooting tree, and, if properly 

 treated, shows no injurious effects from judicious interplanting. In 

 some cases interplanting or double planting with walnuts is practiced, 



