Unheated greenhouse

Greenhouse advantages

An unheated greenhouse is an easy and affordable way of growing vegetables and other plants. It is a strange fact that while every other branch of gardening has made giant strides during recent years the unheated greenhouse still remains neglected and unhonoured. The outdoor border of hardy perennials has its votaries by the thousand, and well it may.

The heated glass-house is to be found in most gardens, but it is a question whether a tenth part of the pleasure can be obtained from it all the year round that may be found in the successful management of an unheated greenhouse by the skilful amateur who, whether he rejoices in the aid of a gardener or no, prefers to keep a corner where he may "potter about " at his own sweet will amongst his plants, and work with his own hands on their behalf. This is mainly due to the vicissitudes of our changeful English climate, which for practically half the year makes outdoor gardening impossible for most people, and the heated house dangerous.

But both the joys of the open garden and, in a measure, even those of the hot-house may be combined and enhanced under the sheltering roof of the unheated greenhouse, as I hope to be able to show in the following notes, which are faithful records of many years of practical experience.

It is well from the starting-point to have a clear understanding of what is meant by a cold greenhouse. It is one in which it is neither convenient nor desirable to have a fixed heating apparatus, and in which it is only intended to prevent the temperature from falling below 35° or, in other words, simply to keep out frost. The term " fixed " is used advisedly, for though there may be cases of glass corridors or of a larger glass-garden in which an ordinary fixed flow-andreturn pipe might answer better than a removable apparatus, it must be borne in mind that the main principle of the unheated greenhouse-except during the few dead and dark weeks which precede and follow the shortest day, or on the occasion of a sudden fall of temperature or of damping fog-is to keep it cool enough for the plants of temperate regions, which alone are suitable to be grown in it. It goes without saying that the mere shelter of glass will not keep out severe frost.

Therefore some means of raising the temperature under certain conditions of weather, to be considered later, are not forbidden to the cold greenhouse ; but artificial heat being, in a general way, not only needless but undesirable, it should be on all accounts as temporary in its character as possible. Heating power of even the most temporary character may be entirely dispensed with, as in the case of an alpinery, which is one of the most delightful forms of the cold greenhouse, but, of necessity, it limits in some degree the choice of plants.

It must be confessed that such unheated glass-houses are by no means in favour. The professional gardener, as a rule, pins his faith to the boiler and pipes, and looks askance at the plants which will thrive in a temperature lower than from 60° to 80°. Tinctured with the hurry and impatience of slow results characteristic of the age, he rejoices in the quick development of fine showy plants, and it is not to be denied that splendid success follows his skilful culture. Much of the success is ephemeral, however, not to say stereotyped. One
may go into greenhouse after greenhouse and find beautiful and well-grown foliage and flowers, undoubtedly, but all of the same stamp. It is seldom that a new and distinct plant arrests one's steps and arouses one's enthusiasm, and how rarely does one see nowadays the grand specimens of hard-wooded plants which were the pride and glory of a past generation, but which took both time and patience to build up.

Today the gardener's art consists in turning out plants wholesale, and it is not too often that he has any incentive from his employers to rise above it, and truly enough it saves a " power of trouble." The amateur, on the other hand, longs to move out of the common groove, and grudges no trouble, but he taxes the capabilities of his unheated house beyond its reasonable limits, and it fails. Midwinter finds him mourning over half-frozen flowers, which, in the quaint phrase of our forefathers, refuse to " blow," and will scarcely even exist. He also, therefore, denounces his cold greenhouse as a fraud, because he has grown plants in it which cannot thrive in a low temperature, and either practically gives it up or orders a furnace. Thus both professional gardener and untutored amateur agree in condemning the cold greenhouse, though from different points of view.

Now my plea is not for unheated greenhouses as against hot-houses. We cannot do without the lovely flowers of the tropics-the Allamandas and Dipladenias, the Palms, and the Orchids, which are such a delight to all flower-lovers. Let us have these by all means, but all the same we need not overlook the numberless hardier plants, not inferior to them in beauty, which are grateful for the simple shelter of glass, and will give us of their best without the expense and labour involved by an elaborate heating apparatus. Believe me, the gardener's-and more especially the amateur gardener's-troubles are not at an end when his greenhouse is fully equipped with boiler and quadruple rows of pipes. Let us, then, consider chiefly the advantages and disadvantages, or rather limitations, of the unheated greenhouse for the practical gardener.


There are hundreds of delicate people who dare not venture to stand about out of doors on a chill autumn or winter's day to superintend garden operations who yet, of all recreations, best enjoy the tending and environment of plants. The relaxing heat of a stove is equally insupportable for any length of time, and abrupt transitions from the moist warmth, even of an intermediate house, into the freezing outer air, or a sudden grappling with a keen easterly blast, is more than even the strongest can stand without risk. It is no small boon, then, on a dreary winter's day to have a place of shelter, neither too cold nor too hot, and a possible occupation where an hour or two may be safely spent in the company of the plants we love.

It is a melancholy fact that the glass-house, seen from outside as a garden adjunct, is not itself, in an artistic sense, a thing of beauty. It is even worse than a mere negative, and sometimes becomes a positive eyesore. All the more reason, therefore, that the inner aspect should atone for the outer, that when we enter it we may be tempted by a genial atmosphere to linger long to enjoy the loveliness of leaf and flower, without a vague dread of an evil genius of bronchitis or rheumatism hovering about us with shadowing wing. If we have the true gardening spirit there will always be some work to do, some new interest to discover.

Outside, the rain may patter on the glass or the bare boughs toss in the whistling wind, and only the pale Hellebore or perhaps a belated China Rose ventures to brave the inclement season before the Snowdrops come ; but within, while we run no risks, we may have greenery and tender spring tints and scents of early Hyacinth and Iris, of Violet and Crocus, and a host of flowers which only ask the gentle coaxing of a little shelter to bless us for our courtesy by stealing, with innocent guile, a few hours from the " winter of our discontent."

Moderate cost

" Who loves a garden loves a greenhouse too," and if this were true in Cowper's day, it is no less true in ours. We are becoming every day more and more a nation of gardeners, and no sooner does the passion for growing plants seize upon us than the necessity of some shelter for them in severe weather makes itself felt. The fine crop of glass-houses which has sprung up over the length and breadth of the land during the last half-century took its origin, probably, from the urgent need of saving through the winter the bedding plants which were to fill the garden beds in summer.

Cheap as glass and woodwork may be now, the greenhouse was formerly in many cases the outcome of much cogitation and self-denial in small luxuries, to end after all, not seldom, in disappointment, for the heating, through ignorance of its need, had been overlooked, and the very considerable expense of a boiler and pipes had never entered into the calculation. Bedding plants are not quite so much in vogue as of yore, but still the wail goes up-scarcely a week passes but it may be heard in country home, in rectory, or in suburban villa-"

We can't save our Geraniums "-geranium being a generic term handy for daily use-" because we have no heat in the greenhouse." And it is very true, for here we come to the limitations of the cold-house. In it we must not expect to grow the plants which require heat in winter to bring them to perfection. Pelargoniums, it is true, will exist in a temperature that never falls below 35°, and some will even stand a slight frost, as is seen by the vigorous specimens to be seen occasionally against a wall under the sheltering eaves of a cottage in Devon or Cornwall, but they are not the type of plant best suited for the unheated greenhouse. Generally, in these cases, it is a question of expense. Either there is no means of heating or no efficient member of the household to discharge the duty of attending to the greenhouse fire, or it may be the cost of fuel which must be considered-with the usual result of a useless greenhouse. Expense may be of little consequence in some gardens, but these are in the minority.

Even to those who are ready to spare no expense the coal bill in these days of exorbitant prices becomes a question of some moment, and it is astonishing what a capacious maw is possessed by the monster called a greenhouse furnace. On the score, then, both of initial cost of a permanent heating apparatus and a constantly recurring expense for fuel, I rest a second plea for the cold greenhouse, in spite of its limitations with regard to certain classes of tender plants.

Simplicity of management

The garden-lover who has no experienced helper-perhaps also some who professedly have-knows full well the wretched trick the furnace is apt to play of going out on the very night of the hardest frost of the year, of pipes bursting at inconvenient seasons, and the misery of finding plants ruined and the work of many a happy though arduous day lost for ever. Needless to descant on the daily and nightly joys of the stokehole, even when all goes well. But if there be risks and impediments such as these when the thermometer falls below freezing-point, there are difficulties more insidious, but none the less real, in regulating a high temperature. Plants grow with amazing rapidity in heat, and the novice is delighted with his early success ; but, alas ! they also lengthen, and before long his plants, like the unfortunates celebrated by Tennyson which were " by squares of tropic summer shut and warmed in crystal cases," are apt to meet the same fate, or

" These, though fed with careful dirt,
Are neither green nor sappy ;
Half-conscious of the garden squirt,
The spindlings look unhappy."

Unhappily, too, other things grow as fast as the spindlings. Aphis is but a feeble foe, comparatively speaking, and easily to be overcome ; but the horror of a visitation of mealy bug -the plague of the hothouse-is not to be described, and scale is nearly as noxious. In the unheated greenhouse the annoyance of such direful insect pests is greatly lessened, and the careful gardener need have none of them. On the score, then, of simplicity of management, I rest my third plea.

To sum up, therefore : For health of enjoyment, for minimum of expense, and for easy handling, the unheated greenhouse presents certain advantages not heedlessly to be overlooked by the lover of plants who makes a hobby of cultivating them for his own pleasure. Add to these somewhat prosaic advantages the great charm of seeking out and making friends with rare and unusual plants, of persuading them to grow and do well under unwonted conditions, of bringing fragments from far distant lands to remind us of happy hours spent under sunnier skies, or of raising seedlings sent from furthest corners of the Empire to show the diverse flora of the environment of new homes. In such manifold ways the cold greenhouse at all times of the year never fails the intelligent gardener. It is subject to no great extremes of temperature, it may be large or small as means or strength will permit, it may be planted out to form a garden under glass, or it may be used exclusively for pot plants. It steps in midway between garden and hothouse, sharing and prolonging the pleasures of the one and giving a safe haven to the refugees of the other.

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