This section is from the book "The Gardener V1", 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.
A HARD winter and dear coals: the former of these conditions is possible; the latter, judging from the present aspect of the coal trade, is certain. The combination is of a character that must of necessity swell the cost-book of all who have to protect tender plants and fruits from frost, especially of those who have to "force early," and keep tropical plants in good condition. How to accomplish this with the least waste of heat consistent with success was never a question of more importance than it is now; at least not since the railroad made coals more comeatable, and consequently lowered their price in many parts of the kingdom. The question is one which of necessity affects a very numerous class, and especially amateurs who have - more from their ardent love of hothouse and greenhouse plants - been impelled into their culture without, at the same time, having a wide margin of wealth to make them indifferent to or independent of a few pounds more or less spent on coals. Hence we conclude that any hints which may be of use to a class who constitute a large number of our readers, cannot be uninteresting at this season, with the prospect of dear coals and the possibility of a hard winter.
Among the principles of culture which bear favourably on economy in this point, stands somewhat prominently that of low night temperature, which has lately been very ably discussed by several of our correspondents. If this principle be correct at any season of the year, the next four months - which constitute the season of rest to most plants - is certainly the most expensive heating season of the year, and, to our mind, the season when low night temperatures are safest. As has been frequently pointed out, a high night temperature, when we have barely eight hours' daylight and sixteen hours of darkness, is attended with the most unnatural and debilitating consequences to plants. Of course there are extremes towards the other end of the scale of heat on which it is not safe to experiment. But, from observation and personal experience, we are quite convinced that our tropical plants, if properly treated in summer, will bear a lower winter night temperature not only with impunity but with advantage. We could instance numerous instances of great success attending this practice.
In our own experience the finest crop of Pine-Apples we ever produced was from plants that stood through a very severe winter in a pit, in which, for weeks in succession, we could not keep the thermometer from falling to 45° at midnight and at daylight. We had considerable anxiety about the consequences to a very fine lot of plants. But when the starting time - about May - arrived the result was as we have stated; and except in the case of Pines intended for starting into fruit in January, we would be quite satisfied with 50° during very severe weather, and 55° as a maximum in mild winters. As compared with higher temperatures, this effects a great saving in coals. We have recently inspected a mixed collection of Orchids, including especially Vandas in more than usual vigour and substance, which was wintered last year at a temperature many degrees lower than the standard temperature generally recommended in the case of such plants. And we were particularly struck with the broad stout leaves and dark green of the Vandas and other East Indian Orchids. It must, however, be stated that to winter such plants at so low a temperature requires some difference in their treatment during summer when they make most growth.
And having named Vandas, we have no hesitation in saying that as a rule they are grown with far too much shade and too little air in summer. The consequence of this is an attenuated, soft, drooping foliage which would not be safe in a low night temperature in winter. But given a Vanda with broad, short, thick leaves, standing at almost a right angle with the stem, and we have no hesitation in saying that it is perfectly safe at 55° at night all through a hard winter. The same remarks apply to Pines and all tropical plants. To winter perfectly they must not be steamed and stifled into mere weeds in summer.
Another point of economy, and also one that may be regarded as good culture, is to apply coverings to the surface of the glass when the weather is cold. This is a great point of economy in firing, and one that is attended with good results to the plants. There is no reason why all comparatively low pits and houses should not be covered at night in severe weather; and we are certain that many will endorse our views and experience that it saves much coal, and is better for Pines and winter Cucumbers to keep up the required temperature by the assistance of coverings, than to do it by sheer hard firing without them. To arrest the immensely rapid radiation of heat that goes on from the surface of a glass-house, where a comparatively high temperature is required, by a covering, cannot but be beneficial in its results to plants as compared with highly-heated pipes and comparatively parched air. And to any one who has a small glass-house from which frost has to be excluded, we say, cover as much of it, especially the roof, as possible; it will save your coals and be vastly better for your plants.
But there are many of our readers who have to protect plants in pits to which no fire-heat can be applied, and to whom the foregoing remarks are comparatively valueless. A few remarks as to how they can best cope with hard weather may be opportune at this the approach of winter; and we will here repeat part of instructions which we wrote twelve years ago. There is one condition at which they must aim, of the very first importance - that is dryness. Whenever tender plants have to be saved by mere protection, dryness is of vast moment. All about the pit should be dry, and the inside of it should be open and thoroughly drained. Indeed, if a staging slightly elevated above the floor can be afforded all the better. To prepare the plants for a long cover up and darkness in such pits, they should be kept dry to the drooping point. They should also be regularly exposed to air during dry weather. This, and the removal of all decayed or crowding foliage in the case of Geraniums and other soft-wooded plants, assists in producing a state of maturity and firmness and rest too, which will enable them to withstand a cold, confined, damp atmosphere, and the absence of light, with the least possible injury when they have to be covered up for days, and it may be weeks at a time.
The manner in which such plants are covered and uncovered during a severe, and it may be a changeable winter, has much to do with success. The best non-conducting material is some dry loose material, such as hay or straw, and the drier and more loosely it is applied the better. In covering with, perhaps, a mat and dry litter, the too common method of applying them is first to lay the mats on the glass, and the loose litter over all. This should just be reversed; the litter should be put next the glass, and the mat over all, making sure that the hay or straw lies as loosely and open as possible, thus ensuring as much air amongst it as can be. A piece of strong calico or canvas dipped in oil, to make it waterproof, is about the best outside covering for cold pits.
When from continued frost it becomes necessary to keep the glass closely covered up for many days at a time, and especially if the temperature in the pit should recede below the freezing point, the great error into which many fall is to uncover the plants immediately the weather changes to a thaw. This sudden uncovering to light causes such a reaction as is ten times more damaging than a few degrees of frost. Plants are living things, possessing all the sensibilities of the most perfect and delicate organisms, and are as susceptible of injury from sudden changes as is the animal frame. Sudden change should not therefore be produced; for, if they are affected with frost, a too sudden thaw ruptures their tissues, and rottenness ensues. Do not hastily remove the covering nor at once, but some time after thaw sets in, and by degrees, and so allow the frost to creep gradually out as it crept in. This is acting on the same principle practised by the cook in thawing her Cabbage slowly in water, instead of hastily in warm water.
In the one case the process is so gradual that the vegetable tissue does not suffer; in the other case it experiences such a rupture that the wholesome vegetable soon becomes poisonous.
The successful wintering of tender plants, whether in cold frames or in hothouses, depends very much on the way they are managed in summer and autumn. It can easily be understood how any tropical plant, be it Orchid or any other stove plant or Pine-Apple, which has been grown all summer in a temperature that is too high, and with too little air and too much shade, becomes so tender as to render it not safe in a temperature where one differently treated in summer would not only be safe, but in the best possible keeping; so that in the one case there is not only an injurious waste of coal in summer, but there is also, from the flabby immaturity of growth thereby produced, a necessity for the same waste in winter also. Let Vandas, for instance, be grown with a proper complement of air and light, and a less enervating heat in summer, and a very small collection will be almost constantly in bloom; while one similarly treated will yield a comparatively small portion of bloom spikes, and be more like a Leek in the flabbi-ness of its foliage.
The same principle of culture applies to many other plants of the most costly description; and we shall be glad if these remarks lead our correspondents to give their views and experience of this subject.