416 
THE COTTAGE GARDENER. 
March 3. 
movning, we are surprized to see every twig and leaflet 
adorned with lioar frost. A clearing of the sky had cooled 
the points of grass and twigs, and by allowing them to 
part with their heat, they thus became so many con¬ 
densers for changing invisible vapour into pearly drops, 
and the radiation continuing longer, the drops were con- 
I gealed into flaky ice. When we speak, therefore, of 
I covering-up from frost, we really mean preventing the 
plant and the earth around it from parting with their 
heat. 
i The recent cold weather has brought these matters, 
: just now, before our attention. The manner and the 
! material best fitted for protecting tender plants become 
i thus matters of importance. Without troubling our- 
! selves with exceptional minutiae, we may set it down as 
j a general applicable rule, that the less dense the material 
used, the (jreater will be the protecting poicer. This will 
appear when we consider, first, that heat radiates from 
the surface; that the layer immediately beneath then 
parts with its heat to restore the equilibrium; and that 
thus the process goes on in a direct line, until, in con¬ 
tinued frosts, considerable depth is reached. The mere 
knowledge of this is of importance, when, in an emer¬ 
gency, we are scarce of litter to throw over our pits and 
frames in severe weather, or when we wish to use it as 
economically as possible, as the shaking up and turning 
the surface of what we have got breaks the line of 
radiation, and forces the refrigerating or cooling process 
to commence anew'. We have even found, in severe 
weather, that the breaking of the surface of .snow with a 
rake was of advantage to plants beneath. Where there 
was great thickness this would scarcely be necessary, as 
the lightness of the snow and the air enclosed with it 
; w’ould be a sufficient protection to the hardier plants. 
Then, again, the same fact will appear, when we 
consider, that so far as the practical operations of gar¬ 
dening are concerned, the conducting-of-heat properties 
of a body will be in proportion to the increase in its 
density. Hence the different sensations we continue to 
! experience, when, in a cold morning, we take hold, re- 
I spectively, of a bar of iron, and a rod of wood. The 
latter, from its weak conducting power at the place we 
grasp it, soon becomes of the same temperature as the 
hand ; hut the bar of iron w'ould continue to conduct 
I heat from the hand, until the hand and the rod became 
Ik 
I of an equal temperature. Hence the folly of using zinc 
I or galvanized iron, however light and neat, as shutters 
I for plant-houses. Hence, in structures roofed with 
metal, their great heat in summer, and the increased 
: cold in winter. If we place a plate of metal, and a 
thickish board of wood, respectively, firmly on the 
ground, and examine them after a severe frost, we 
shall find the earth under the first firmly frozen, wliile 
under the w'ood, it will be little more affected than may 
j he accounted for by the loss of heat at the sides by 
. radiation. Hence, too, the reason why frost will pene- 
j trate deeper, and heat likewise, into ground that is 
! smooth and hard, than into that which is open, porous, 
I and rough. The reason why we advocate a water- 
j proofed covering for frames, &c., is that the moisture 
increases the density of the covering material, and thus 
furnishes strength to the radiating and conducting-of- 
heat powers. 
'J'hen, kee])ing in view how a canopy of clouds 
in a summer's eve preveirts the earth being cooled, we 
are furnished with a key as to the best manner of 
applying protecting material. Whether the tender- 
plant is in the open air, or under glass, the plant and 
the glass will be best secured by having an open space 
between them and the protecting medium. The extent 
of that space must be regulated rather by financial 
considerations than by scientific deductions. Three 
inches will be good; six inches better; and twelve inches 
superior still. The covering, and the thing protected, 
just act and react upon each other, then, like the earth 
and the cloudy sky; nay, more than that, the enclosed 
air becomes a first-rate protecting medium. We have 
said that radiation and conduction are regulated by the 
density of bodies—but what loss dense than air? and 
then, when confined, it is one of the very best non¬ 
conductors of heat we possess. Hence, one of our 
correspondents, some time ago, recommended double 
sashes for houses aud pits, thus getting rid of a mass 
of littery protecting material. With a space of six 
inches between the sashes, or even less than that, and 
the sashes fitted close to isolate the enclosed air, from 
our own experiments, w'e should conclude that coverings 
would very seldom be necessary. But then there would 
be first expense. Any of our readers, however, who do 
not use above half their sashes in winter, will find 
great advantage by making them double, by placing the 
unused ones over the others in severe weather. Double 
boll or hand-glasses, will also be of great use for tender 
plants out-of-doors, such as those that require protection 
only when young. Single hand-lights of large size, 
and glazed tight, will also be of great use, as tlie air 
within will be confined and still. Whatever is used, 
whether glass, waterproofed cloth, or even evergreen 
boughs, let the protecting medium be at a slight distance 
from the plant. 
For combining neatness, utility, moderate first ex¬ 
pense, and ultimate economy, we recommend, for all 
glass-covered pits, &c., wood shutters made of half-inch 
or three-quarter-inch best deal, and painted a stone 
colour after tho wood is thoroughly seasoned. If a 
temporary frame of wood is fixed to the ends and sides 
of the sashes, some two inches deep, and the shutters 
are made to fit close, a body of air will be enclosed 
that will render other covering unnecessary, while the 
skeleton frame will save the paint of the sash when 
sliding the shutter. The same mode may be pursued 
with asphalte, or with straw, mats, or cloth fastened to 
a frame, and made waterproof, but none of these modes 
will so thoroughly combine efficiency, neatness, and 
ultimate economy. When none of these modes are 
resorted to, but a clean mat or cloth is placed over the 
glass, and then, in severe frost, hay and straw are placed 
above to keep the cold at a distance, both trouble, and 
the necessary quantity of litter, will be minimised by 
having a waterproofed cloth or canvass to throw over 
