anadian HorticoltOrist 



Volume XXVIII 



SEPTEMBER, 1905 



mm 



Number 9 



HOW TO FORECAST FROSTS 



J. B. REYNOLDS, O. A. C, GUELPH, ONT. 



IN districts where the cultivation of fruit, 

 flowers, or vegetables, is highly spec- 

 ialized, it becomes important to possess 

 means of forecasting frost at critical times 

 during the growing season and of prevent- 

 ing injury from low temperatures. I'his 

 article is written with the object of giving 

 some practical suggestions on these matters. 

 TOPOGRAPHIC. 



Land, bordering on the water front is less 

 liable to extremes and to low dips of tem- 

 perature during the growing season than 

 inland districts. This is one of the reasons 

 that the best fruit sections are found by the 

 water. Apart from the steadying influence 

 of the water in lessening the chance of 

 damage, frost is essentially a question in air 

 drainage. 



In a given district, the spot where night 

 frosts are most likely to occur is the one 

 with the lowest elevation. There is a case 

 in point along Lake Ontario east of Stony 

 Creek. From the lake back to the moun- 

 tain there is a belt of land with a topogra- 



phy similar to the illustration, Fig. i. On 

 the side of the mountain there is a terrace, 

 at A, where plums and pears are success- 



fully grown. From the foot of the moun- 

 tain the ground slopes gradually as at B. 

 There grapes and peaches are grown. At 

 C is a depression, from which the ground 

 rises both toward the lake and toward the 

 mountain. Experience has shown that 

 fruit growing is much more precarious at 

 C than at A or B. The reason is found in 

 the topography in spite of the greater near- 

 ness of C to the water. At night, the cold, 

 heavy air drains away from the mountain 

 side toward C. If there were no rise of 

 ground as at D, the air would drain to the 

 lake, and C would be as immune from frost 

 as A or B. But on account of the peculiar 

 slope of the ground the cold air from the 

 mountain side lodges at C, and here the low- 

 est night temperatures are likely to be found. 



ATMOSPHERIC. 



It is frequently possible to forecast frost 

 from the appearance and condition of the 

 atmosphere toward the afternoon. After 

 a north wind has been blowing, with a clear 

 or clearing sky, there is likely to be a con- 

 siderable fall of temperature. Specifically, 

 a clear sky, and a still, dry air, are favor- 

 able to frost. Conversely, if the sky is 

 cloudy, or the wind high, there is less chance 

 of a fall of temperature. 



Given a still air and a clear sky, the 

 humidity of the air, the amount of moisture 

 in it, is the chief factor in controlling the 

 night temperature. The temperature will 



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