284 Strawberry-Growing 



crates per acre, which sold for $113.32 gross; so that the 

 net profit, after deducting the cost of crates and picking, 

 was $258.29 per acre, and we still have heaters on hand." 

 If a thermometer placed near the surface of the ground 

 reads 37 degrees or less by two a.m., and no clouds or 

 mist are rising, it is advisable to start the fires. 



Light frosts may be warded off by building large fires 

 at the lower end of the field. The hot air rises and cold 

 air rushes in to take its place, so that a current of air 

 sets toward the fires from all parts of the field that are 

 higher. When air is kept in motion there is not likely to 

 be a frost. 



If the ground is wet thoroughly, either by sprinkling or 

 by irrigation, the evening before a frost is expected the dan- 

 ger is lessened, since the increased amount of water vapor 

 in the air raises the dew point. If frosted plants are 

 sprinkled at daybreak, before the sun thaws them, they 

 are not likely to be injured, even though they were frozen 

 severely, since the water makes them thaw out gradually. 

 Until recently, this was practicable only in home gardens ; 

 now the overhead system of irrigation by sprinkling pro- 

 vides means for doing this commercially. It is necessary 

 that the nozzle line shall rotate every four or five minutes, 

 so as to keep all the plants wet. It is possible that heating 

 the water used in the sprinkling Systran may be found 

 practicable. 



