This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
Dear Sir, - I wish to ask you the above question; pray do not dismiss it and me, as too stupid to be answered. I am but a novice, and "merely ask for information." It is, I believe, usually insisted upon by gardeners, as very necessary; and I concede that for plants grown in the ordinary manner, and for ordinary purposes, the common practice is correct. What, then, am I after] Pumping into and out of a barrel is effected in the same way; I want to know which way we pump. Do wo open to let in air, or to let out heat? If a pipe ran through the top part of a house, and when cooling (miscalled ventilating?) was necessary, cold air or water were forced through it, or cold water were run over the roof, would not that answer as well as sliding down the sashes? If the temperature never rose above the desired point, would ventilation be necessary?
In most houses, plants are grown with a view to setting out in the open ground; is not the much insisted upon ventilation, simply a "hardening off," acclimating process, not necessary if the plants were intended to remain in the house 1 There is a wide range in the temperature desirable for plants; the minimum of some, is the maximum of others; it also varies for the same plants, according to the state they are in; the ordinary gardener has to try and strike a happy medium. If but one kind were in a house, were intended to remain there, and the proper amount of heat and moisture were never exceeded, would ventilation be necessary?
Airing cabbage and lettuce frames is strongly insisted upon in all gardening books I have read, and unless it is done, they spindle; does this arise from the plants needing air, or from the fact that they will not stand a high temperature, and that in consequence of thick sowing and board frames, they are deprived of proper side light?
Perhaps you will think that as I acknowledge the common treatment to be right, the reason therefore is of little consequence - the difference " 'twixt tweedledum and tweedledee ;" but I think things are best called by their right names, and therefore do not see why what, in my humble opinion, is a false reason should pass current If ventilation is necessary, our furnaces are improperly fixed; it is as easy to give plants fresh air in winter as in summer, if you will pay for it - in fuel. The heating surface should be cased and air warmed as it enters, as in dwelling-house heaters of proper construction; and I think this to be the best way to warm conservatories, or piazza greenhouses; the atmosphere would be more agreeable and healthy for the owners and their friends, if not for the plants.
[Our practical friend is always most welcome. We are ever ready to assist him, and all our readers, to the best of our ability. Things, undoubtedly, ought to be called by their proper names. Whatever the gardener's theory may be, practically he opens his house to reduce the' temperature, though in the act he of course lets in fresh air; but the reduction of the temperature is the ruling idea, how-ever, and not the admission of fresh air, in the great majority of cases. The two ideas will naturally be associated by an intelligent mind. We may say, therefore, that ventilation is not resorted to until the temperature has risen above a certain point. In regard to your next question, we may say, "ventilation " is a "hardening off" process for plants intended to be transferred to the open air; a gradual approach to the atmosphere in which they are finally to grow. Next, if but one kind of plants were in a house, and the proper amount of heat were not exceeded," ventilation " would not be necessary. This is but a corollary of what has been said before.
Again, cabbages, etc., " spindle " not only because they are sown thick, but because a nigh temperature causes them to grow too rapidly; the liability to " spindle," however, decreases very much in proportion to the amount of room each plant has to grow in. But in regard to this whole matter, we may say briefly, that a circulation of air, in connection with a suitable amount of moisture, .is more important than a change of air. This circulation, where the needed moisture is present, is often afforded by the simple changes of atmospheric heat; though this, again, is dependent to a considerable degree upon the construction of the house. A dry, hot air is prejudicial to most plants; and the admission of cold air in such cases often only substitutes one evil for another. That "ventilation " is often carried to an excess, we have no doubt; and this will continue until the subject is better understood and the whole system changed. We simply say for the present, give your plants plenty of room, plenty of moisture, and " ventilate" as little as possible.
With every caution, the excess is likely to be on the wrong side. - Ed].