176 CALIFORNIA FRUITS: HOW TO GROW THEM 



is given promptly and in sufficient quantity. There must alwavs 

 be a determination of what is an adequate supply by reference 

 to local conditions, but as an estimate of necessary rainfall has 

 been made at 20 inches, it is evident that adequate irrigation may 

 be very much less than that. The rainfall of 20 inches is dis- 

 tributed through six or seven months. Some of it consists of light 

 rains, with long, dry intervals, where there is slight penetration 

 and quick evaporation. Some of it is lost by run off and by 

 drainage. It is not surprising, then, that some growers having 

 deep valley loams to render their irrigation effective, report success 

 with deciduous trees with 8 or 10 inches of water applied just at 

 the time of the tree's greatest needs and used, no doubt, with 

 maximum efficiency. It seems to be a warranted deduction, frorn^ 

 all data known to the writer, that 10 inches of water, applied at 

 the right time to soils of good depth and fair retentiveness, and 

 accompanied by good tillage for conservation, is an adequate sup- 

 ply for five months of growth and fruiting even when the rainfall 

 is only about enough to prevent drying out during the winter 

 season. Some growers report use of less than this. Certainly 

 less will do for young trees under favorable conditions, and some 

 of the least amounts are reported from the newly planted regions. 

 As the trees advance in age and bearing, larger amounts will be 

 required. Instances of greatest frequency of application may be 

 taken as indicating soils lacking retentiveness, either through shal- 

 lowness or coarseness, or either of these accompanied by extreme 

 summer heat and aridity. 



Citrus Fruits. As these trees are evergreens, and as their habit 

 is to make their chief fruit growth in the autumn after the work 

 of the deciduous tree has been finished for the season, the irriga- 

 tion season for them is much longer. As they are, in fact, almost 

 always active and sustaining uninterrupted evaporation from their 

 leaf surfaces, they must always be provided with moisture or ill 

 will result to tree or fruit. They thus require more water than do 

 deciduous trees. There is the same relation between irrigation 

 and rainfall with citrus as with deciduous fruit trees, but the degree 

 of relation is different. Many trials have shown that it is prac- 

 tically impossible to grow satisfactory citrus fruits without irri- 

 gation, unless there be underflow, and this is attended by the usual 

 difficulties of high ground water and undesirable. There is no 

 combination of heavy rainfall, or winter irrigation, and soil reten- 

 tiveness which will supply the summer and autumn thirst of the 

 orange or lemon in California. Irrigation, too, must be maintained 

 both summer and winter wherever the rainfall is not well dis- 

 tributed and adequate. In the chief citrus regions of the State 

 rainfall is seldom adequate except during January and February, 

 and not always then. Under such conditions an estimate of the 



