228 



RULLETIN 89 



wide draws, affording excellent air drainage to the valley below. 

 Coupled with this ideal topography there is an almost constant 

 circulation of air. Observations on the Mesa covering a period of 

 twenty-six years (the age of the oldest citrus planting in this dis- 

 trict) with accurate weather records covering the greater portion 

 t)f this time, show no serious injury from cold. In the disastrous 

 treeze of 1913 when the temperature in the Southwest v^as lower 

 than had been known for a period of sixty years, lemon trees on 

 the Mesa were only slightly affected, the thermometer registering 

 from three to eight degrees higher than in the citrus districts of 

 California. It can. therefore, be stated most positively that the 

 frost hazard, a matter which should receive first consideration in 

 the selection o/ a location for citrus growing, is a negligible factor 



Fit 



.",. — Wiiidlireak of evergreen tamarisk on tlie Yuma Mesa, 18 months 

 from planting 



in this district, and should give the prospective citrus grower no 

 concern. In view of the great expense involved in the use of 

 smudge pots, as practiced in some of our older citrus regions, im- 

 munitv from frost injury is an item of extreme economic import- 

 ance. 



Weather records kept at the Blaisdell Orchard from October, 

 1893, to June. 1987, are given in Bulletin 58 of the Arizona Agri- 

 cultural Experiment Station and are reproduced here in Table I. 



