34 DROUGHT KESISTANCE OF OLIVE IN SOUTHWESTEKN STATES. 



AREA OF POSSIBLE DRY-LAND OLIVE CULTURE IN THE UNITED 



STATES. 



AREA LIMITED BY THE MINIMUM TEMPERATURE. 



Of the factors defining the area of ohve culture in the United wStates, 

 that of minimum temperature is the most important. 



It has been claimed by some authors ® and by many olive growers 

 that an actual minimum temperature of 14° or 15° F. will prove fatal 

 to the olive tree. It is undoubtedly true, however, that the olive 

 will endure considerably more cold than this if it is in a thoroughly 

 dormant condition. This is especially true where the atmosphere 

 is dry and where the low temperature persists for only a short time, 

 possibly a few minutes at near daylight, as is so often the case in the 

 southwestern sections. 



As an illustration of these ideas, in 1899,'' from February 11 to 13, 

 a cold wave of unusual intensity swept over a great portion of the 

 Southwest, temperatures of -6° to —23° F. being recorded in north- 

 ern Texas, and as low as 8° F. in the southwest border. 



At San Antonio two stations gave minimum records of 4° F. At 

 Fort Mcintosh, on the Rio Grande near Laredo, a minimum tem- 

 perature of 5° F., probably for only a brief period, was recorded 

 on the morning of February 12, and at Fort Ringgold, 90 miles dowQ 

 the river, a temperature of 7° F. was recorded on the morning of 

 February 13. 



An olive grove of an acre or more about 2 miles from Fort Mcin- 

 tosh suffered some killing back, though the trees were not seriously 

 injured and may be seen to-day looking as vigorous as any in the 

 olive-^rowdno; districts of California or Arizona. 



At the dry-land experiment station of the Bureau of Plant Industry, 

 near San Antonio, Tex., young olive trees of the Chemlali variety 

 endured a minimum temperature during the winter of 1907-8 of 18° 

 F., with but a slight killing back at the tips. Yet in 1909 these olive 



a A temperature of 5° C. below zero (or 23° F.), followed by a sudden thaw operated 

 by the sun's rays, is sufficient to kill it totally at the base. With a lower temperature 

 not followed by sunny days the plant does not suffer as much, as it can stand a cold 

 of 10° C. below zero (or 14° F.). — Olive Culture, Italy, Annual Report of the State Board 

 of Horticulture, California, 1890, p. 449. 



"A low temperature, say 14° F., is fatal to the tree."— 5. M. Lelong, Investigation 

 Made by the State Board of Horticulture of California Olive Industry, Sacramento, 1900, 

 p. 8. 



"The olive can grow in all regions where the minimum temperature does not fall 

 below —7° or —8° C. and does not last more than eight days." — Translation from 

 Hidalgo Tahlada. 



b Annual Summary, 1899, Texas Section, Climate, and Crop Service, Weather 

 Bureau, U. S. Dept. of Agriculture, 

 192 



