LETTUCE 



221 



lettuce prefer 40 to 45 degrees at night and 10 to 15 de- 

 grees higher by day. 



Most growers of Grand Rapids lettuce maintain higher 

 night temperatures than they did a few years ago. For- 

 merly, 45 degrees at night and 55 to 60 degrees by day 

 were standard temperatures among the best gardeners. 

 Now, some of the largest growers prefer 48 to 50 degrees 

 at night and 55 to 60 degrees by day. A night tempera- 

 ture of 45 degrees with high humidity and wet foliage is 

 likely to cause much more damage than a temperature 

 of 50 degrees with low humidity and dry foliage. On 

 warm, sunny days during the spring, no harm will be 

 caused by temperatures of 75 degrees or above, provided the 

 houses are well ventilated. It is always important to have a 

 definite understanding with the night fireman and watchman 

 concerning the temperature that should be maintained. 



Fig. 75. The lettuce in this large range is cultivated with a 5-pronged weeder 

 attached to a long handle. 



Ventilation. Much has been said on previous pages 

 about the importance of ventilation. In lettuce culture it 

 is one of the means of avoiding losses from the attacks 

 of fungous diseases and of producing the best, most com- 

 pact heads. On very cold or stormy days the ventilators 

 are not opened at all, while in mild weather it is not un- 



