Suitable and unsuitable plants for a greenhouse

It is natural enough for those who are young in gardening matters to be disappointed when they are warned that plants from the hardy and half-hardy classes only must be reckoned upon for cold greenhouse culture. What is the use of a greenhouse at all, they are ready to ask, if only common, everyday flowers can be grown in it ?

Let me try to expound both its use and its charm. The craving for flowers is universal, but in winter we want them in our rooms rather than out of doors. The garden has a winter beauty of its own, and we know and love it well, but it is not the beauty of flowers. The tracery of bare boughs against the sky, the glow of scarlet Holly berries midst polished leaves, the quiet grey tones of Rosemary and Lavender-all these in their various ways give a sense of restful waiting for the coming activities of spring, and they are very dear to us.

But all the same we want flowers, for, lacking two things, books and flowers, no home looks home-like. We can buy them, doubtless, but " boughten " flowers do not satisfy the craving that will not be still, and we wander out into the garden ready to welcome the homeliest floweret which has dared to brave the winter storms.

What are we likely in most localities to find ? Christmas Roses maybe, but besmirched ; Snowdrops, not always snow-white, unless, haply, a carpet of turf lies spread beneath them ; Laurustinus -except in the milder South-hopeful-looking at a distance, but sear and brown on closer view ; the earlier Crocus buds and Primroses wantonly nipped off by saucy sparrows ; the rest, as yet, awaiting their awakening. A handful of purple-brown Mahonia leaves, a few battered flowers from the China Rose in some sheltered corner, some clustering Ivy or a spray or two of variegated Box-these form the sum total of what many a garden gay enough in summer is able to produce. Whether we will or no-rare cases excepted-for our winter posy we must needs go to the greenhouse. Call to mind the most common everyday flowers that we know-Daffodils, Hyacinths, Wallflowers, Stocks, Crocus, Forget-me-not, Violets-and think whether a greenhouse filled with such as these would not be an enviable possession from Christmas onwards ?

And then, again, if we are not flower-lovers merely, but plant-lovers-a very different cult-how keen is the disappointment when, after months of patient tending of one and another of the lovely green things upon the earth which are to us as priceless gems, we are robbed of the full fruition of our labours by treacheries of weather or hungry bandits in the shape of slugs and snails ! The open ground is no safe place to which we dare trust our rarest treasures, and a sheltering frame becomes a necessity, and sooner or later the frame will need expansion into larger space, where we may group and make pictures of our plants and enjoy them to our heart's content.
Yet it is a mistake to think that hardy flowers need be common.

The finer varieties are always worthy if we take the pains to seek for them ; and it is their earlier flowering under shelter, no less than their own beauty and sweetness, that gives them their claim to the greenhouse. A greater mistake still would be to think that even such everyday things will bless us with a grace so early, unless we lay our plans with intention and remember cheerless winter days to come when summer yet holds her lap full of flowers.

Hardy plants for the greenhouse

Let us try to define the distinction between hardy and half-hardy plants from the point of view of the unheated greenhouse. Hardy plants, as we know, are those which need no protection to enable them to withstand the frequent changes of our climate in all parts of the United Kingdom, but for greenhouse purposes we must gather out of these such as can be made decorative either for foliage or for flower during the flowerless season. Roughly speaking, this season extends from October, when the first keen frost sweeps its sharp scythe over the autumn garden, until March-in some years later still-when swelling buds and the blackbird's mellow pipe begin to tell us that spring is here. Before Christmas, Chrysanthemums, late Tea and China Roses, a few annuals especially prepared, like Cosmos, the crimson spikes of Schizostylis, Carnations of the Margherita type, late purple Asters too tardy to open out of doors, and many another bright flower will come to our aid.

With the new year, and before if we try, we can have Roman Hyacinths, paper, and the early Scilly White Narcissus, scarlet Van Thol Tulips, and Christmas Roses, while the cheerful gleam of Coronilla and Winter Jasmine and the lovely cream-white flowers and buds of the Box-leaved Myrtle and of Laurustinus will not leave us forlorn even at that pitiless season. Then will follow a long procession of spring bulbs, herbaceous perennials, and shrubs, which it is our business to coax into flower to fill in the remainder of the weeks until the greenhouse needs no longer to take the place of the outer air.

So much as this, and, indeed, much more, may be done without any firing at all, for these are all hardy plants, but not without some extra care when the weather is specially severe, and maybe, on occasion, at the cost of a little drooping, not very harmful, of the more tender flowers. Not without energy, and perseverance and forethought besides, for the winter campaign must be prepared for in two ways-(1) by retarding such summer flowers as can be kept back to bloom in the latest autumn, and (2) by bringing spring plants into flower before their due season. Midway between these two comes another class, of which early Rhododendrons and Azaleas are a type, which flower naturally almost at midwinter, but seldom escape unhurt if they remain unsheltered.

A limit, indeed, can scarcely be put upon the hardy spring flowers-Anemones, alpine Primulas, Orobus, Saxifrages, Cyclamen vernum, and Doronicums-to name but a few out of a host which lend themselves with gratitude, and enjoy such gentle forcing as the shelter of glass can give them. They come from many lands, and often from climates much more rigorous than our own, but where they are neither puzzled by the wiles nor entrapped by the cruel ogre of the weather, who entices them with smiles one day-to gobble them up on the next.

There is but one hardy plant which for this purpose, perhaps for its very hardiness, I, for my own part, would not choose-the low-growing herbaceous Heath (Erica carnea). Be the winter what it may it never loses heart of grace, but bides its time. It may blush into perfect beauty a little sooner or a little later, as the season lets it, but no storm seems to harm, no stress to change it ; all hurtful creatures pass it by, only the bees murmur over it their first happy thanksgiving as they sip the nectar from its tiny flasks. Most flowers we love to gather and bring indoors, but not this one. True child of the mountains and the moor, it asks no shelter ; let us leave it to its liberty, for, as it seems to me, it is happier so.

Half-hardy plants for the greenhouse

It is customary to count as half-hardy many of the soft-wooded plants which are used for summer bedding, such as Pelargoniums, Heliotrope, Ageratum, Cupheas, and the like, but it is a misleading term as far as the unheated greenhouse is concerned, for in no part of the British Isles will these survive a winter out of doors, and they might perhaps be more accurately described as sub-tropical. It is true that Pelargoniums of certain sorts thrive all the year round in sheltered spots in the Isles of Scilly, but whole hedges of them were cut down to the ground-line in a disastrous winter some years ago when there was a most unusual visitation of 0° of frost. It is also true that they will exist under glass in a low temperature, but it must always be above 40° Fahr., for they quickly damp off unless there is enough warmth to keep them in a growing state, while to have zonal Pelargoniums in bloom during the winter requires not only a season of special preparation beforehand, but a temperature equal to summer heat ; hence it is plain that they cannot be recommended for the cold greenhouse.

Ordinary greenhouse plants, again, such as Libonia floribunda, Bouvardia, Chinese Primula, and even Persian Cyclamen must be put out of our thoughts, though the last two do excellently well in the windows of light warm rooms. it must therefore be clearly understood that by " half-hardy " in these pages it is intended to express the degree of hardiness which will pass safely through an ordinary winter in the Isle of Wight or in Devon and Cornwall, and which is able to endure a trifle of frost for a short time in a dry, still atmosphere without permanent injury.

But even for half-hardy plants like these the mere shelter of glass will not suffice, because the advantages of climate afforded by the South Coast are exceptional, and therefore if we decide to grow the more tender amongst them we must make up our minds to provide some temporary means of raising the temperature in severe weather. Amongst the half-hardy plants that are suitable under these conditions we may include some of the Heaths and handsome South African Crassulas and Mesembryanthemums, as well as Gladioli, Lachenalias, Crinums, and other bulbs from the same regions, the Disas and some terrestrial Orchids of Table Mountain ; Acacias, Boronias, Correas, and other hard-wooded plants from Australia and New Zealand ; strange Cacti and Mamillarias from the arid plains of the southern United States ; Rhododendrons from the Himalayas, verily a goodly company, with infinite variety from which to choose.
It may be added that the two classes of hardy plants and half-hardy plants overlap each other, and that some things reckoned tender will survive when hardier ones fail, but the reason is probably found to be some accident of individual constitution rather than in any question of temperature. Many of the plants here mentioned require special treatment and are not altogether easy to succeed with, e.g., the hard-wooded Australasians, which are, nevertheless, well worthy of all the pains and care that can be bestowed upon them. Others, again, like the Cape bulbs, present no difficulty of culture when once their management is understood, as in the case of Nerines, while succulent plants are the most long-suffering of all green things, living and often even thriving under positive neglect, yet rewarding, many of them, the most moderate understanding of their wants with largest interest of brilliant and sometimes gorgeous flower.

It is very needful that the distinctions which I have tried to make clear between plants suitable and unsuitable for the unheated greenhouse should be carefully noted, for nothing but disappointment can follow an attempt to make a simple glass shelter do duty for a house capable of being heated up to Orchid or even Pelargonium pitch. No less important is it clearly to define our intentions to ourselves as to whether we grow hardy plants only or whether we wish to include the less hardy, for which a certain amount of heating power is required, though not enough to render the term " unheated greenhouse " a contradiction, inasmuch as it need be in most cases merely a transient encumbrance and not a permanent one. In either case some knowledge of plants and a hearty desire to know more is inseparable from the true enjoyment of this, or, indeed, any other branch of gardening.

With regard to culture, nothing teaches so much as practice, and when the true gardening instinct exists the early stage of helpless ignorance soon gives place to greater assurance, as we take advantage day by day of every hint, spoken and written, that comes in our way. Then as experience grows we begin to make experiments on our own account, for there is no doubt whatever that many plants may be educated and made to adapt themselves to environments other than those that are natural to them, and herein lies one of the many interesting features of advanced work in a cold greenhouse.

A generation since, numbers of plants now commonly to be found in our garden borders were grown under glass and reckoned too tender to be trusted out of doors. The result of experiments during many years in testing the capabilities of unheated houses in my own garden proved to demonstration that a fair proportion of plants will succeed admirably under good management, and are less subject to blight and disease in a much lower temperature than is usually supposed to be indispensable to them.

The same effects, it is true, may be traced as the result of the different modes of treatment, as may be noticed in Switzerland between the plants of the valley and those of the bleaker mountain-side-the growth is not so rapid, and luxuriance is restricted. But what is lost in these respects is made up in added vigour of constitution and greater power of resistance to the attacks of insect pests, and even in more abundant flower. Therefore, in choosing plants for the unheated greenhouse we may lay aside all misgivings, so long as we make no mistakes between plants suitable and unsuitable to be grown in it.

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