FROST. 



Frosts are most injurious to plants 

 at 50° Fahrenheit, in full vigour of 

 growth ; hence a slight frost in spring 

 usually destroys expanding buds and 

 the young shoots of vegetahlcs. It 

 may act in a variety of ways, but 

 commonly by freezing the sap of the 

 leaves, which produces a disorgan- 

 ization of its tissues. Frosts l)y ra- 

 diation occur sooner in elevated sit- 

 uations, at a distance from lakes or 

 rivers, than in valleys that are kept 

 moist. Whatever intercepts the 

 clearness of the sky diminishes or ar- 

 rests frosts ; thus, clouds, a large 

 quantity of vapour in the air, smoke, 

 or mattmg. straw, glass, boards, &c. 

 Hence, gardeners cover tender plants 

 with leaves, straw, pine brushwood, 

 or protect them with mats or glass ; 

 in such cases, the radiation is from 

 the mats, &c., and not from the 

 plants. Watering plants abundantly 

 at nightfall, when the evening ap- 

 pears clear and frost may be appre- 

 hended, is often efficacious ; water- 

 ing before sunrise, after a slight frost, 

 is also valuable, for the vapour of 

 water, in both cases, acts as a cover- 

 ing to the vegetation ; in the even- 

 ing it diminishes radiation ; in the 

 morning it gently warms and thaws 

 the leaves before the destructive ac- 

 tion of the sun can take place. Trees 

 are often preserved by twining a 

 quantity of rope among their branch- 

 es and allowing the ends to dip in wa- 

 ter. On a larger scale, the Indians 

 of Cusco used to burn large quanti- 

 ties of moist straW' and leaves at sun- 

 set when a frost was apprehended, 

 and thus, by obscuring the sky, hin- 

 der radiation. During the winter a 

 coating of snow is a remarkable pro- 

 tection to a crop, maintaining it at a 

 regular temperature, while the ex- 

 posed surface would have been much 

 injured by severe frosts. A bed of 

 snow, eight inches thick, frequently 

 measures 10° Fahrenheit at the sur- 

 face and 32° Fahrenheit at the earth, 

 and, being a very bad conductor of 

 heat, changes its lower temperature 

 ■very slowly. 



Flooding meadows to such a depth 

 that the earth may not be frozen is 

 310 



one of the most certain and effective 

 means of saving grass and advancing 

 it in maturity for the next spring, the 

 water being withdrawn when the 

 weather has become mild and free 

 from frost ; lands over which fogs 

 lie long are also well protected from 

 early frosts. Exposure has also much 

 influence on the early occurrence of 

 frosts ; lands which receive the 

 least sun and are exposed to chilling 

 winds being visited much sooner than 

 those looking to the south and shel- 

 tered. 



The night frosts produced by radi- 

 ation are very different from the cold- 

 ness of the air in winter. The cold 

 of wmter does not act precisely like 

 early frosts ; valleys are sooner afTect- 

 ed than hillsides unless they contain 

 water, and this is supposed by Lind- 

 ley to be produced by the descent of 

 cold air from above into them, but 

 is also due to the lesser duration of 

 sunshine. During our winters the 

 sun usually retains much power, so 

 as to produce thawing in places where 

 his direct beams fall ; this elTect ta- 

 king place suddenly, and often upon 

 trees or vegetable structures, is very 

 injurious, so that delicate trees are 

 often destroyed in orchards facing 

 the southeast from this cause, espe- 

 cially in the spring. Sudden thawing, 

 whether taking place on a leaf, tree, 

 or root, is much more injurious than 

 freezing ; for the expansion produced 

 in the gases of the plant causes them 

 to rupture the cells and become mix- 

 ed with the fluids, thus commencmg 

 decomposition. It is a well-known 

 fact that potatoes, &c., may be kept 

 frozen for a year or more without in- 

 jury, if they be thawed gradually by 

 immersion in spring water ; but if 

 they be exposed to a hot sun, or 

 thrown into hot water, they become 

 disorganized, and rot at once. Hence 

 the policy of the gardener and or- 

 chardist is to plant orchards and ex- 

 pose early vegetables and products in 

 such a manner that changes from 

 heat to cold may be gradual, and 

 not sudden. The retardation of flow- 

 ering in a northern situation, in fruit- 

 trees, is amply compensated by tho 



