PROTECTION OF GARDENS FROM FROST. 87 



;;n attempt will be made to apply the principles and methods which 

 have been tested in the protection of citrus and deciduous fruits from 

 frosts to the protection of gardens. A word of warning at the outset. 

 It is very probable that as we apply these different methods we shall 

 find different efficiencies, and it may be that some especially efficient 

 method may be worked out for gardens, entirely different from those 

 best suited for fruit. In brief, as each rancher has had to determine for 

 himself the special method best adapted for his locality, his crop, and 

 the time of the year which is most critical for him, so each gardener 

 must work out his own individual problem. The general conditions 

 preceding frosts, the physical processes at work in the formation of 

 frost, and the different ways of remedying the ill effects of a sudden fall 

 in temperature, can be given; and with these the gardener must deter- 

 mine for himself by actual tests the most efficient processes for his 

 particular garden. 



LIKELIHOOD OF FROST. 



Frost, as a rule, occurs in California between the middle of Octo- 

 ber and the first of May, although light frosts have occurred in the 

 Sacramento Valley, for example, as late as May 17. The particular 

 frosts with which we are concerned in the protection of vegetable and 

 flower gardens are the frosts of February, March, and the first two 

 weeks in April. Inquiry of the Weather Bureau at any date in March 

 will elicit information as to whether frost is likely to occur on that 

 night or not. In the absence of such information, and if the gardener 

 is without a sling psychrometer (which, by the way, no skilful gardener 

 or orchardist should be without), a clear, still night following thirty- 

 six or forty-eight hours of boisterous north wind is to be considered 

 dangerous. Frost occurs whenever the movement of the air in a local- 

 ity has been such as to result in a settling of cold and relatively dry 

 layers in hollows or even slight depressions of the land. The forma- 

 tion of frost is essentially a problem in air drainage, and if by any 

 means we can prevent these pools or basins of stagnant, cold, dry air, 

 we can prevent largely the formation of frost. It may be pointed out 

 that what we call frost is the deposition of the water vapor upon the 

 plant at a temperature of 32 degrees or bielow. What really does the 

 damage to plant life is the fall in temperature, and the water vapor only 

 plays the part of an exponent. Indeed, the action of the water vapor is 

 preventive, and, as we shall see further on in connection with delicate 

 flowers, a coating of ice is in many ways one of the best protections 

 against injury. Every gardener, therefore, should familiarize himself 

 with what may be called the air drainage system of his locality. So 

 long as the air is in motion, the temperature is less apt to fall to a low 



