CONSERVATIVE WALLS. 
181 
even to thrive in spite of all deterring circumstances : but see them when the 
autumn frosts and the cold damps of winter follow — they are cut down, and 
perish. It is one thing to grow a tender plant in the open air in summer, and 
another to preserve it alive and healthy through a dark cold winter. 
In selecting a site for a conservative wall, considering the point entirely in a 
cultural light, (it has been before viewed as a matter of taste,) a low situation 
exposed to fogs and damp should be rejected ; for it is a well-ascertained fact, that 
plants so situated suffer injury and die in a winter that leaves the same species 
perfectly unharmed in a more elevated spot. And again, it is not advisable that 
walls built with this intent should be in anywise shaded by trees, or even have 
large trees in their immediate vicinity, as, independent of other injury, the plants 
in such places are more liable to be attacked by mildew. 
The borders, moreover, should be as carefully constructed as for a forcing 
vinery ; well-chosen materials, and ample facility for getting rid of superfluous 
water must be provided, and efficient steps taken to prevent the roots of one plant 
from piercing the soil and pilfering the nourishment intended for a less robust 
neighbour. The soil of course must be varied to suit the species planted ; it will 
be enough to say here, that all clayey earth of a tenacious quality, and light sandy 
soils that part too freely with their moisture, should be refused ; the first is 
especially hostile to the culturist, through the quantity of water which it holds 
keeping the roots at a lower temperature, and rotting them ; and also because it 
offers a repulsion to the delicate fibrils in their efforts to penetrate it : the latter is 
obviously incapable of affording sufficient sustenance to the generality of plants in 
a moderately dry summer. A great depth of soil is quite superfluous, and even 
injurious, as it draws the roots away from the surface ; two feet will be found 
quite sufficient, and this should be laid dry, by placing a quantity of draining 
materials below it. The bottom, too, should have a gentle slope from the wall, 
and be flagged, or laid with some asphalte mixture, so that it may be quite 
impervious to the roots, and thereby restrain those organs from pushing too deep, 
and sucking up matter to be spent in producing a redundant luxuriance, and 
continuing growth longer in the season than the sun has power to mature it. The 
breadth need not exceed three feet. 
Further, as many of the plants usually placed against a conservative wall, will 
vary from each other very much in their relative strength, the border should 
always be divided into compartments, so that the roots of one plant may never 
infringe on the supply of food designed for another. This is a point worth looking 
to, wherever promiscuous planting is intended ; for, without such a curb, the 
stronger invariably overpower the weaker. Slate is perhaps the most eligible 
substance for the purpose, as it occupies little space, and is easily concealed at the 
surface. 
Besides one plant to remain permanently, each of these divisions of the border 
may hold one or two dwarf plants of rapid growth, intended only to remain during 
