This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
THE past winter, and some of the lessons it has been calculated to teach horticulturists, will long be remembered. In some districts, and probably in the south-west of Scotland in particular, there is no record of cold so protracted and severe. For the sixty-two days of December and January there were 11° of frost for each day, and, including February, there were 9° frost for each of the ninety days of the three months; and while we write - 11th March - the frost is not yet out of the ground.
Some writers have been reckoning up the injury done to vegetation by the very long period of low temperature, but we consider it even yet too soon to arrive at a correct estimate, vegetation being unusually late, and, until the sap begins to rise more freely under the influence of more sun, the results cannot be wholly visible. Common vegetables have suffered to an extent that we have not witnessed or heard of in forty years' experience. We have seldom seen Roses so severely injured, notwithstanding the fine ripening effects of the last warm summer and autumn. Although the time has not yet arrived to determine it, we have a suspicion that Pear-buds are very considerably crippled; but as the full extent of the injury done to outdoor vegetation cannot yet be correctly estimated, we will turn to another department of horticulture, in connection with which some very forcible lessons have been given by such a winter.
In the early forcing department the effects of the long cold season have been most apparent in the slow and comparatively little progress of such crops as early Grapes, Pines, Peaches, Strawberries, etc. No doubt experienced gardeners may now be able to make up some of the lost time by a more rapid forcing pace. Though this may to some extent be a necessity, it is not by any means a desirable one. Beyond doubt, those who have attempted to force early Vines and Peach-trees, having their roots chiefly in outside borders, have reaped an experience that ought to demonstrate the absurdity of the theory held by some, that earth-heat is an immaterial condition. To force Vines, with their roots in a much lower temperature than the atmosphere of the vinery, is one of the most flagrant violations of the laws of nature, and to arrive at anything like thoroughly satisfactory results, by practically controverting these laws, is impossible. This subject has been warmly discussed at intervals, since ever we had any acquaintance with horticultural literature, and, perhaps, never more warmly than during the last twelve months. It is, in truth, remarkable that this should be the case.
The marvel appears to us to be that more efficient arrangements have not long ago been adopted for affording more favourable, because more natural, conditions to the roots of Vines and Peaches that are forced throughout the winter months.
Covering up the borders in early autumn with non-conducting material to conserve the natural heat of summer, and the allowing of that heat first to escape, and - at midwinter when forcing is commenced - to force more heat into the border by means of a hotbed of litter and leaves, are the two systems pitted against each other by controversialists. In a certain way, and to a certain extent, these systems answer the end in view. But neither the way nor the extent are good imitations of the natural way. They are, however, in many instances, the only available methods. The objections to them are, in the first place, that they are laborious and very untidy; but our greatest objection is that the surface of the border is reduced to an unnatural state of soddenness, and the roots near the surface are very apt to be roots that are very easily injured when the mucky coverings are removed.
It is astonishing, now so many Grapes are forced early, that vineries are not erected on more correct and rational principles for this purpose. In the construction of early vineries and peacheries a much more efficient and natural way of preserving the natural heat of autumn in the soil, and of augmenting it at the proper time, should be provided for. This could be done much more effectually, and in the long-run at less expense, than by the cumbrous, untidy, and to some extent injurious, systems in common practice. The winter and early spring heat necessary to the stems and foliage of Vines, which in summer is chiefly supplied by the sun, we supply by the best imitation of nature within our reach - namely, hot water; and we are of opinion that a modification of the same principle would be the most efficient and best way of affording heat to the roots that are not under the same roof with the stems. It may be asked, Why not have all the roots of early Vines in the vinery? That certainly would be a step in the right direction. But we have noticed, in a long experience, that Vines with their roots all inside a narrow border, have never been so satisfactory as when a considerable portion of them were in outside borders.
And supposing that the roots are equally located in an inside and outside border, and that they do best so (as we believe they do), why not, now that glass is so cheap, efficiently cover the outside portion with a glass case, and run a flow, or flow and return, hot-water pipe through it. It would be the simplest thing imaginable to have a stout movable framework for the border of the early vinery, with a pipe attached to the inside pipes, that could be removed in summer - frame and pipe and all - with the greatest of ease. In midwinter the surface of this glass case could be covered with mats or frigi-domo, and, when the sun gains power in February and March, sun-heat could be shut and covered up in it, just as in the vinery itself. It may be argued against this that the border heats slowly from the top. We think this is an assumption, and nothing more. The natural heat of the earth in summer is surely the result of heat from above, as well as the prevention of radiation from a certain depth below the surface.
One of the greatest obstacles in connection with the early forcing of Pines, Vines, Peaches, Strawberries, Cucumbers, etc, which has no doubt been forcibly experienced during the recent severe time, is the lamentably unmethodical - we had almost said stupid - way in which the houses are too frequently arranged and placed in relation to each other; when, as is very often the case, all these crops have to be forced simultaneously. Even in many of the most pretentious gardens, the arrangements are what may be termed the most haphazard and inconvenient. The various houses are dotted about, just as if there had been a shower of them. Their relations with each other, and with the heating-power, could scarcely be more stupidly planned. In many cases the houses are widely apart; or, if nearer each other, they are often on different levels. Every one of these early forcing structures should be, if possible, in the same range: the floors and hot-water pipes in the whole should as nearly as possible be on the same level, where all, or several of them, are heated by one boiler. The heat can then, in a severe winter and spring, be much more nicely balanced (as much by a judicious allotment of pipes as by valves) than when pipes from the same boiler are working at different levels.
This is a principle far too much ignored in erecting forcing-houses. And we appeal to those who have had experience of forcing-houses at different levels, heated from the same fire, if the attendant evils have not been very conspicuous during the past winter, when hard firing had to be resorted to.
Small houses, necessarily enclosing a small or thin volume of air, are strongly advocated by some, as capable of being kept at a more equable temperature in cold, fitful, winter weather. A recent writer in a contemporary has laboured hard to prove this; but his demonstration appeared to us to be very lame and defective. Our experience, not to speak of anything else, has taught us the very reverse, and we have always found a small narrow structure fluctuate much more sensitively to the influence of cold or sun-heat from without. The principle involved we conceive to be the same as that by which a thin bar of iron, or a thin anything else, cools more quickly than a thicker one. We have for years cut Grapes and gathered Peaches in April from houses only 8 feet wide, and have done the same from much larger houses, and always found the larger ones more easily dealt with in the matter of steady temperature. And we consider no early vinery or peach-house, to be satisfactory in this respect, should be less than 16 feet wide; and we shall be disappointed if many early forcers have not verified this in the last severe winter.