These properties of the soil relatively to plants can never be completely attained by growing plants in pots, and least of all by growing them in pots surrounded by air. In this state, whatever may be the care of the gardener, a continual succession of changes of temperature will take place in the outside of the pot, and the compact material of which it is composed being a much more rapid conductor of heat than porous earth, it will soon be communicated to the web of roots within.
With respect to water, a plant in a pot surrounded by air is equally liable to injury. If the soil be properly constituted, and the pot properly drained, the water passes through the mass as soon as poured on it, and the soil at that moment may be said to be left in a state favourable for vegetation. But as the evaporation from the surface and sides of the pot, and the transpiration of the plant goes on, it becomes gradually less and less so, and if not soon re-supplied, would become dry and shrivelled, and either die from that cause, or be materially injured by the sudden and copious application of water.
Thus, the roots of a plant in a pot surrounded by air, are liable to be alternately chilled and scorched by cold or heat, and deluged or dried up by superabundance or deficiency of water, and nothing but the perpetual care and attention of the gardener to lessen the tendencies to these extremes could at all preserve the plant from destruction.
To lessen the attention of the gardener, therefore, to render the plant less dependent on his services, and, above all, to put a plant in a pot as far as possible on a footing with a plant in the unconfined soil, plunging the pot in a mass of earth, sand, dung, tan, or any such material, appears to us a most judicious part of culture, and one that never can be relinquished in fruit-bearing plants with impunity. Even if no heat were to be afforded by the mass in which the pots were plunged, still the preservation of a steady temperature which would always equal the average temperature of the air of the house, and the retention, by the same means, of a steady degree of moisture, would, in our opinion, be a sufficient argument for plunging pots of vigorous growing, many-leaved, or fruit-bearing plants.
Such are the observations that we think may be made relatively to Mr. Knight’s plan, without prejudice to whatever new lights he may throw out on the subject. Had it been brought forward by a less eminent horticulturist, it would not have claimed so much attention, as the plan of growing Pines without bottom-heat is generally considered to have been tried first by M. Le Cour, and subsequently by various others, and abandoned. In Mr. Knight’s hands, however, whether it fail or succeed, it is certain of doing good, by the observations it will elicit from the fertile and ingenious mind of so candid and philosophical a horticulturist.
Sir William Edward Rous Boughton has erected a house or pit at Downton Hall, similar to that of Mr. Knight, but rather wider.[2] Pines are grown in it on Mr. Knight’s plan, but the plants were not in a thriving state in November last. Charles Holford, Esq. of Hampstead, is also a disciple of Mr. Knight as to the culture of this fruit, but he has not yet been very successful.
[2] The roofs, both of this house and that of Mr. Knight, were furnished by Messrs. W. & D. Bailey, of Holborn, London.
Sect. II.
Of other Improvements in the Culture of the Pine Apple, by different persons.
We shall first notice the improvements which respect bottom-heat, and begin with noticing an attempt made by Mr. Thomas Jenkins, of the Portman Nursery, London, to warm both the pots in which the plants are grown, and the air of the house, by the heat generated by fermenting stable-dung placed in a vault beneath.
It is only within the last three years that Mr. Jenkins has begun to grow the Pine Apple to any extent; he brings forward the plants in hot-beds and deep frames, inclosing beds of tan, and heated by linings of dung. As an economical part of the construction, we may mention that he substitutes wattled hurdles for the lower part of the frame, in contact with the tan, by which means a saving in the first cost is effected, and the heat of the dung penetrates much more readily to the tan.