The book of the greenhouse

Front matter

Class Book

HANDBOOKS OF PRACTICAL GARDENING EDITED BY HARRY ROBERTS

WITH A SPECIAL CHAPTER ON THE LITTLE TOWN GREENHOUSE

Contents

PAGE

Editor's Note . . ..... vii

Structural ....... i

Chapter I Structural

No garden can be considered complete or satisfying to its possessor, unless it contain a greenhouse in which may be cultivated beautiful -flowers and plants that are impossible in this country without the aid of glass and protection. To the plant lover, one or more of such structures will, if well placed, well fitted, and, especially, well filled, be an endless source of pleasure, and peculiarly so during the dreary period of the year when plant life is more or less dormant in the outside garden. Probably most of my readers already possess a greenhouse, but it is to those who contemplate adding such a building to their possessions that this opening chapter is directed, with a hope that the hints which it contains, though necessarily in few words, will be helpful.

The site for a greenhouse should be selected with care, bearing in mind that it must be well exposed to day-light and, if possible, well sheltered from easterly and northerly winds. As a sunk furnace is easier in working and less wasteful of fuel than one set on the level, the house should stand on fairly high and well drained ground, so that there may be no trouble from surface water. No trees should overhang or even be allowed near enough to the house to shade it at any time of day.

Span-roofed houses, i.e. those with two equal sides to the roof, should always be built with the ends facing

A i north and south, and if one end is formed by an already existing wall this should be the north end. Such houses

are more easily managed, and their occupantsalways happier than is the case with houses built from east to west. A span-roofed house, built sufficiently wide to permit of a central stage in addition to two narrow side stages, is perhaps the very best possible form of house, as its occupants can always be arranged so that they may be seen at their best, but, where the width is only sufficient to admit of two side stages with a path down the centre, I consider the span a wasteful form of house and one in which plants can never be arranged to look well, as, unless the house is lofty, the tallest plants are perforce brought next the eye and the others graded away from, instead of towards, the path.

Lean-to houses are those in which the roof takes one slope only from back to front. For a position against a wall this is the cheapest and perhaps the best form of

VENTILATION BY MEANS OF FRAMED LIGHTS

STRUCTURAL greenhouse. It may be built with any aspect from south to west, and for certain purposes, such as the cultivation of Ferns, a house of this form facing north is most useful. The worst aspect of all is towards the east.

The internal arrangements should consist of a narrow front stage, then the path, leaving the biggest space for the back stage. This latter may be built in tiers like a series of steps if the height of the roof permit, and will then present more staging room as well as bring the back plants nearer the roof — an important matter in plant-growing under glass.

The Hip-Span is a useful form of house for building against a wall too low to suit a lean-to. It is a combination of the span and the lean-to, the short "hip" or span at the back adding height and forming a convenient position for the ventilators. The above forms of houses are those most in use, and any departure from or combination of them is only carried out for the sake of ornament.

Next in importance to the building itself comes the ventilation of the house. Elaborate ventilating arrangements are by no means necessary, but provision must be made for an ample supply of fresh air when it is needed. By an ample supply I do not mean that there is need for many different sets of ventilators, for these often lead to draughts which are inimical to plant life and breeders of mildew. Ample means of admitting air must be given at the apex of the roof, and these roofventilators must be continuous throughout the whole length. Those houses which have some of the rooflights fixed and others made to open are sure breeders of insect pests, besides endangering the plants beneath such fixed lights by scorching. Too much importance cannot be placed on the value of ample top ventilation, as the air may thus be entirely changed without creating draught. In comparison with the top ventilators, those at the sides or bottom of the house are quite unimportant ; indeed, many of the best plant growers of the present day never use side ventilation at any time, reckoning it not only useless but harmful for many plants, as it dissipates too readily the natural humidity created in a houseful of plants, and which the great majority of plants enjoy. Some plants, however, prefer a dry atmosphere, and for these side ventilation should be arranged and used cautiously : a few small sliding shutters placed low down, so that the fresh air may feel the influence of the hot water pipes in cold weather, will suit the requirements admirably.

We will now consider the question of the stages or benches to be used. This is not the unimportant matter that it is often considered to be. I attribute many of the failures and the successes largely to the staging arrangements of the house. The most common method of staging plants is to put them on benches formed of narrow strips of wood placed an inch or two apart, thus having an open space between them. This I consider to be quite the worst form of staging, and more especially so where the hot water pipes are placed immediately beneath such stages, for the fire heat necessary in very cold weather does much harm to the root action by over drying the pots, and thus killing the tips of tender rootlets. Undoubtedly the best of stages are formed by good thick slates, as these are always cool and slightly absorbent, so that the bottoms of pots standing on them never become really dry ; but slates are expensive to begin with, and wood does nearly as well provided that the boards are placed close enough together to support a surfacing of shingle, ashes, or some other covering of an absorbent nature. A narrow strip can be nailed round these wood benches to retain the inch or so of this material. All stages placed over hot water pipes

STRUCTURAL should be carried quite back to the wall on the one side and project well beyond the pipes on the side next the walk, for heat striking directly on to plants from the pipes is the cause of much mischief.

For propagating purposes, I would suggest that where only one greenhouse is possible it should always contain

LEAD BAR GLAZING a propagating box of some kind. This should be fixed at a convenient point where it may enclose some portions of the hot water pipes, which may then be buried in a good depth of cocoanut fibre. This box may be a fixture, or may be movable, so that it will only be in the house when needed, but it will be found a most useful adjunct, and will provide means for raising young plants of all descriptions either from seeds or from cuttings.

Glazing. — I do not propose to enter into much detail as to this. Personally, I prefer the system of glazing without outside putty, as it appears to be the most drip proof system when the houses are well looked after as regards painting. One special point must be emphasised as regards glazing. This is to use only the best twentyone ounce glass. Inferior glass is a misery to the plant grower, the bladders and flaws it contains acting as burning glasses, and so giving much trouble.

Shading. — Protection from the sun during the hottest portion of the day is quite necessary for many plants. The best way of shading a house is to use roller blinds, as these may be run up or down at any time according to the weather which prevails. They are also useful during the winter as a slight protection from frost and as a saving of fire heat. Blinds are, however, somewhat expensive items, for exposure to all weathers causes them to perish quickly. Roller blinds made from laths or narrow strips of wood are not to my mind so effective as they were at one time considered to be.

The cheapest method of shading consists in painting the glass with whitening mixed with milk, or with the very useful mixture known and sold as " Summer Cloud." For the grower who cannot always be on the spot, something that is to a certain extent permanent during the summer months is necessary, and these washes provide a cheap and effective shade. The objection to them is that they are on in dull as well as in fine weather, but this is counterbalanced by the fact that they are always on the spot when needed, and this cannot always be said of movable blinds however careful one may be.

Heating.— The heating of greenhouses has gone through many phases during the past half century, but I think that at last we may claim to have a really good system in the use of hot water for the purpose. It is a matter for congratulation that the old system of using hot air flues has almost disappeared, as these flues were almost always a nuisance ; they cooled quickly if the fire went low, were often difficult to heat, and, worst of all, they were prone to leakage, and once the sulphurous fumes got through to the house, they meant death to the plants. I should not have mentioned the flue system of heating at all, did I not know that flues are to some extent used even now, and sometimes advocated for their cheapness. On the whole, we have nothing yet to supersede hot water when driven by a good boiler through a sufficiency of 4-in. pipes. Steam heating is quicker in action, but requires more attention from the one in charge, and it is not so manageable as hot water, especially for houses small in size and in number.

Dealing, then, with ordinary hot water heating, it is necessary to success that the boiler be set well beneath the level of the house, that the pipes be so fixed that they have a continuous rise in the upper or flow pipe from the point of connection with the boiler to the point farthest away from it, and that the under or return pipe have a corresponding fall from the highest point reached back to the boiler again, which it should enter near the bottom. Speaking generally, the greater the rise the better the circulation must be. It sometimes happens that a doorway or some other obstruction engenders a wish to allow a " dip" at some particular point, but to do this will be fatal to successful circulation. "Where two or more houses are connected with the same system of piping, valves should be put in the pipes so that the heat may be wholly or partially shut off when not wanted in a particular house or compartment. An air-tap should be connected to the pipe at the highest point so that any accumulation of air that would stop the circulation may be expelled at this point.

The heating arrangements of a greenhouse must of

STRUCTURAL course be governed to some extent by the class of plant it is to contain. Cool house plants, and even so-called hardy plants, when grown in pots, must have some fire heat in winter. For such things two rows of 4-in. piping running lengthwise and across one end of the house would be sufficient. For the warmer greenhouse four rows of 4-in. piping traversing the same distance would be necessary. An approximate estimate is that I foot of 4-in. piping will heat moderately 30 cubic feet of space, but it should be borne in mind that it is far better to have too much than too little piping, as the heat given off to keep up a given temperature will be less fiery and injurious in proportion to' the additional piping used. In choosing the boiler do not be misled into getting one that is too small for its work. Allow a broad margin beyond the maker's estimate of size necessary to heat a given quantity of piping. A new boiler well fixed and driven hard by constant attention may do all that is claimed for it at first, but will not continue to do so for long without more attention than one is prepared to give it. In any case, the amount of necessary attention is less with a fairly big boiler than it is with a small one.

The Garden Frame. — An indispensable companion to the greenhouse is the portable garden frame. Under good management it will never be empty for long together, and will act as a feeder to the greenhouse proper, for in it can be raised and " grown on" plants innumerable, which will in their turn help to embellish the more pretentious structure. Its several uses will be mentioned as I deal with the cultivation of plants in other chapters, and this must serve as an apology for so briefly dismissing it in this.

CHAPTER II Hard- Wooded Plants for the Greenhouse

As a preface to the cultural portion of this little treatise I should like to say that it will be impossible to deal in a satisfactory way, in the space at my disposal, with all or even with a large portion of true greenhouse plants, as the result of so doing would be to compile something scarcely better than a catalogue, and of little, if any, value to the reader. I propose, therefore, to deal in a general way with the management of the various sections, each section as a unit, and to particularise only in the case of plants which are fairly common in cultivation and such as the great majority of plant lovers would wish to grow. I regret that many charming species will thus be left unmentioned and must be sought for in works of greater pretension.

Hard-wooded plants, so called, are mostly of bush shape and shrubby habit, though many climbers are also included in this section. Familiar examples of plants comprised under this heading are Azaleas, Ericas (Heaths), Camellias, Cytisus (Genistas), Epacris, Boronias and Daphnes. A few years ago one would have included many more as familiar plants, but unfortunately the easy culture of the many soft-wooded plants has led to the discarding of plants more beautiful, when seen at their best, than many of the favourites of to-day.

Hard-wooded plants as just implied are as a class a little difficult to grow well ; for, though some few of

IO them will bear a certain amount of rough treatment and neglect, they can only be well grown when all their wants are carefully attended to. The majority have small hair-like roots which, though numerous, have no great capacity for storing moisture, hence some of the difficulties of their culture for, if over-watered, the roots cannot assimilate the surplus quickly and the soil under its influence turns sour, while, on the other hand, if allowed to become dry, the tiny tips of the roots wither and are not easily or quickly replaced — indeed, plants of some species never recover from the effects of being allowed to get thoroughly dry. Most of the plants in this section like a peaty soil, the majority succeeding well in a mixture of two-thirds fibrous peat, one-third fibrous loam and sufficient silver sand to make the mixture feel thoroughly gritty when handled. It is not necessary to repot every year, indeed with care in management several years may elapse between the pottings, but when it has to be done, either through a noticeable want of vigour in the older plants or from a desire to grow younger ones on into fine specimens as soon as may be, special care is needed in carrying out the work in all details. Clean pots must be used ; if the insides be left dirty the new roots will stick fast and be wrenched off at the next potting. The new pots should not greatly exceed in size those from which the plants are to be transferred. No new pot should be used until it has been soaked in water for a few hours and allowed to get dry again.

Drainage should be thorough : this does not imply an excessive use of crocks, but rather that those used should be well placed in the pots and covered with a little of the toughest fibre that can be selected from the soil heap and freed from all fine particles. Previously to being turned out of the old pot, the plant to be operated on should be watered just long enough to allow of the soil being in that nice condition known as neither wet nor dry, and the new soil should be in about the same condition, i.e., damp enough to bind together when rammed, yet not so wet as to become pasty with ramming. Sufficient new soil should be put into the new pot to elevate the ball of soil and roots attached to the plant, which has been previously freed from the old drainage material, high enough to prevent any portion of the stem which has hitherto been uncovered from becoming buried in the process of potting, as to bury the " collars" of these plants is generally injurious and often fatal to them. Some of the more delicate species, indeed, do better and live longer when the " collar" is left slightly higher than the surrounding soil. To complete the potting in a workmanlike way the old ball of soil should be placed exactly centrally, so that there may be an equal distribution of new soil all round it, and this should be put in a little at a time, each successive layer being well rammed home, leaving no crevices, until the potting is complete. Potting should take place at a time when the roots have resumed activity after a slight rest. This will in most cases be when the new growth, made after flowering, has been perceptible for two or three weeks. As the period of growth varies according to the different species and their time of flowering, no particular period can be mentioned, except that it is some time during spring or early summer.

Most of the plants in this section are essentially what are known as cool greenhouse plants and are very impatient of fire heat at any time. This, combined with their inability to withstand frost, renders their cultivation a matter of careful watching and solicitude on the part of the grower. In the winter, the temperature of the house may safely be allowed to fall within a very few degrees of freezing point, when the outside temperature is very low ; this will be far better than firing up to maintain the 45 which is considered to be the regulation minimum temperature in normal weather. At all times there should be ventilation, and even in frostyweather some air should be admitted through the top ventilators, indeed, when the weather is mild, full ventilation from all points, short of creating great draught, ought to be provided, the only time when one can permit oneself a little license in the way of keeping the plants somewhat closer than usual being just for a week or two after they are potted, to encourage root growth. It must always be remembered that the new annual growth must be given full opportunity of becoming well ripened before winter, and this cannot happen in a close atmosphere. During the brightest weather of the spring and summer months, a light shade may be necessary ; but full advantage of the autumn sunlight should be taken to ripen up the newly made growth. In some cases it is an advantage to put the plants in the open air during autumn, plunging the pots in ashes to prevent the roots from parching, and to leave them out while the weather remains fine and mild ; but they must on no account be left out in continuous rain.

With regard to watering, sufficient has been already said as to the care which should always govern operations. Plants must not be allowed to be dry for long together, neither must they be watered before they have reached that stage of dryness at which water is needed. No exact rule can be laid down to indicate when a plant should be watered, and experience is the only safe guide to the requirements in this way ; the gaining of this experience being the one great stumbling block which stands in the way of the would-be grower of hard-wooded plants. A fairly safe test is, however, the old fashioned one of tapping each pot with the knuckles. If the result is but a dull response, such as one would get from tapping any solid body, no water is required ; but if a hollow or slightly ringing sound be produced, then the time for watering has come. Should the ringing be accentuated, the plant should be plunged in a pail of water and left there for a few minutes to absorb as much as it can and to allow the water to reach the middle of the ball, dryness of which is not easily remedied by giving water in the usual way through the spout of a watering-pot. The avoidance of such excessive dryness as this, however, should be one of the chief cares with the grower, as fatal results of such neglect are to be expected.

Many hard-wooded plants being averse to lime in any form, provision should always be made for a supply of soft water, and if this is not sufficient for all the plants grown in the greenhouse it should be specially reserved for those of this class.

Overhead syringing is not often necessary, though for a time, during the early period of new growth, a dewing of soft water appears beneficial, and the plants certainly seem to thrive under the influence of the heavy night dews which they experience during fine weather when growing in the open air.

Insect pests do not as a rule give much trouble to hard-wooded plants which are well looked after and well treated, but there are some which trouble certain plants, as for instance : Thrips are partial to Azaleas, Scale in variety to Camellias, White Scale to Neriums (Oleanders), Red Spider to Pimelias, and some of these plants have a common enemy in them all. Needless to say, the plants cannot thrive under attacks from these pests which sap their life blood and choke their pores with filth. In the matter of dealing with insect pests, however, the present day grower lives in comparative joy, for science during the past few years has produced many insecticides

'7 that enable us to cope with the enemies to plant life by safer and more effective methods than any that were formerly in vogue, and there is now but little excuse for dirty and insect-ridden plants.

When ventilation has been insufficient and the outer atmosphere foggy, Mildew becomes a great enemy to many hard-wooded plants, notably to Heaths, and as it is very insidious in its attacks it should be carefully looked for. A speck or two of decay among the tiny leaves of Heaths, or a white mould on larger leaved things will, if unchecked, soon develop alarming proportions. Directly such signs are seen, the plants, and especially the affected parts, should be dusted freely with Flowers of Sulphur, which is an effective antidote to Mildews. A sulphur duster or puff should always be at hand in the greenhouse, and its use never put off when required.

Hard-wooded plants are but rarely propagated in private places. Nurserymen have greater conveniences for this work and can carry it out in bulk, so that each batch of cuttings or seedlings may get exactly what is needed at all times. As this is not possible in a private place and as the process of raising these plants is a slow one in any case, it is always best to commence by buying established plants of fair size which will give a quick return in the way of flowers. Buying them when in flower is not, however, the best way. They should be bought long enough before flowering to get acclimatised in their new home.

CHAPTER III Hard-Wooded Plants for the Greenhouse

continued

Turning now from generalities that may be applied to most plants in this section, I propose to give as fully as may be the details of treatment suited to each genus among those selected as being the most popular and most useful, and will begin with the

Acacias. — Though most of these develop into trees or big bushes in their native habitat, a few are amenable to pot culture, and can be maintained in a small state as free-flowering bushes. They are easily cultivated, and flower mostly in spring, when their innumerable tiny yellow balls are greatly appreciated. Those of which I give the names below may be well grown in small pots, and are therefore the most serviceable. The simple details of culture consist in giving cool greenhouse treatment in winter, allowing during that period a rather limited supply of water, pruning the plant into shape after flowering, potting if necessary soon after new growth begins, and putting them out of doors in a sunny spot during summer, throughout which period the supply of water must be ample. The soil for Acacias should be two-thirds loam, one-third leaf mould, and plenty of sand. A. armata, of which bushy little plants profusely flowered and sweetly scented may be grown in 6-in. pots. A. lineata, A. Drummondii and A. ovata are all good.

Azaleas. — In these we have a genus of plants which,

ACACIA OVATA taken as a whole, is more valuable than any other in the greenhouse. The Indian or Chinese section is the one to which the name of " greenhouse Azaleas" applies most fully, but the Ghent and Mollis types, the little A. amoena, which has proved so valuable for hybridising purposes, and the double flowered A. balsamctflora all have their special value, and must not be omitted. The culture is similar to that laid down in chap. ii. for general guidance, but the Azalea will stand some artificial heat during the period of making growth ; the Ghent, Mollis and Amoena varieties will bear considerable forcing, and provide a blaze of colour during the late winter and spring months. During the warmer parts of the year, the plants delight in being syringed daily. The best time for potting is soon after flowering, but many of these plants are allowed to go for years without potting, and still keep in good health. With the Indian section no pruning is necessary beyond the shortening of a strong growth which promises to destroy the balance of the plant and the removal of very weak shoots. This should be done directly the plants have flowered, and at the same time all old flowers and seed pods should be picked off. Small plants may be put into the garden frame during summer, and the larger ones may be stood out for a few weeks during the early autumn, and brought in again on the approach of frosty nights.

Boronias. — Though not showy as to their flowers, Boronias are greatly appreciated in the greenhouse from the exquisite perfume they emit during the flowering period which lasts over several weeks, one plant being sufficient to fill a large house with its fragrance. The general treatment advised will be found satisfactory, but to it must be added an extra caution with respect to watering, as the plant is quite impatient of an excess, and for this reason it should always be grown under cover, so that heavy rains may not reach it.

Camellias. — The stately if somewhat formal looking Camellia is known to all, and when well grown it makes one of the handsomest shrubs in existence. Its proper place is planted out in the border of a greenhouse or conservatory, but it may also be well grown in pots. As its roots are stouter than those of most hard-wooded plants it requires rather different treatment. At no time does it like to be dry, and plants well set with buds will take a lot of water, varied occasionally with liquid manure, during the time they are swelling. Plants allowed to get dry at the root often drop their buds. During spring and summer they like shade enough to prevent the leaves from scalding. Potting is best done just as the annual growth has reached its full length and before the buds become prominent. Annual potting is not necessary. Plants that set a heavy crop of flower buds should be disbudded, leaving but one bud or, in the case of really strong plants, two buds to a shoot, selecting the largest and the smallest to give a succession of flowers. Camellias require but little pruning and it should be remembered that cutting back a shoot deprives the plant of flowers from the resulting growths for one year. The best growth buds, and the only ones which will produce flowering shoots for the following season, are found immediately below the flowers, and by the time the latter drop the former are quite prominent. If the plants are moved out of doors during the late summer, they should be put in a shady spot at the north side of a wall, as pot plants do not like being set in full sun.