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Forcing. The word forcing is variously used. Properly, it should designate the growing of plants outside their usual or normal season. This distinguishes forcing from the ordinary purpose of the glasshouse, which is to imitate the usual season in which plants grow. For example, begonias are not forced: we endeavor to protect them and to give them the season and the conditions under which they grow in the wild. Carnations when flowered in the winter are forced, because we transpose their seasons. Chrysanthemums blooming in-October and November are not forced: they are only protected. Sometimes the word forcing is used in a very special sense, to denote the production of flowers from bulbs or tubers in a very short time under the influence of a very high temperature. Thus, the lily-of-the-valley may be placed in a temperature of 90° or above, and the large buds be forced to throw out their flowers before the plant secures a firm foothold on the soil.
Forcing. The word forcing is variously used. Properly, it should designate the growing of plants outside their usual or normal season. This distinguishes forcing from the ordinary purpose of the glasshouse, which is to imitate the usual season in which plants grow. For example, begonias are not forced: we endeavor to protect them and to give them the season and the conditions under which they grow in the wild. Carnations when flowered in the winter are forced, because we transpose their seasons. Chrysanthemums blooming in-October and November are not forced: they are only protected. Sometimes the word forcing is used in a very special sense, to denote the production of flowers from bulbs or tubers in a very short time under the influence of a very high temperature. Thus, the lily-of-the-valley may be placed in a temperature of 90° or above, and the large buds be forced to throw out their flowers before the plant secures a firm foothold on the soil.
The accompanying illustrations (Figs. 1541-1548) show old and recent styles of American forcing-houses. For further discussion of glasshouses, see Greenhouse.
The accompanying illustrations (Figs. 1541-1548) show old and recent styles of American forcing-houses. For further discussion of glasshouses, see Greenhouse.
The forcing of vegetables.
The forcing of vegetables.
A moist humid atmosphere is necessary for grapes while they are growing or from the time they are started into growth until they begin to color, from which time a drier bracing air will be of advantage. At this stage, bottom air may be admitted by degrees during the day, and later, or when ripe, keep bottom air on day and night.
A moist humid atmosphere is necessary for grapes while they are growing or from the time they are started into growth until they begin to color, from which time a drier bracing air will be of advantage. At this stage, bottom air may be admitted by degrees during the day, and later, or when ripe, keep bottom air on day and night.
Pruning.
There are two objects in pruning: first, to keep the vines in submission and second, to encourage vigor. For the first season after planting, it would be well to allow the vines to grow freely with very little stopping of shoots. This encourages root-action and if everything has progressed satisfactorily, the canes will reach the top of the house the first season. When pruning time comes, this cane must be shortened back, allowing only about 5 feet of the season's growth to remain. The same method should be adopted the following year and so on till the full height of vine is secured. Before beginning to prune a grape-vine, one should be absolutely sure the wood is thoroughly ripe. This may easily be ascertained from well-ripened wood, for after pruning the cut will remain perfectly dry and in a few days have the appearance of an old cut. On the other hand, if the wood cuts soft with a fluid on the cut, then the wood is not ripe enough. To produce well-ripened wood from the time the crop is gathered till pruning time, an abundance of air should be allowed in the house and when the foliage has completed its functions a dry atmosphere should be maintained and the vines kept fairly dry at the roots. In the long-rod spur system, it is necessary to prune hard back, otherwise in a few years long ungainly spurs will result. One or two eyes to each spur is sufficient and, with thoroughly ripened wood, there is no danger but that a bountiful crop will follow.
Varieties.
There are many varieties for forcing purposes, although only a selection of the best varieties, early and late, is given here. The Muscat grapes are the finest of all the hothouse kinds. Unfortunately they require a longer season to ripen. Consequently one must rely on earlier-maturing varieties for early forcing. A few canes of Muscats may be planted in an early house and they will be useful after the early kinds are exhausted. It is not wise to depend on thin-skinned Muscats for late use, as there would be difficulty in keeping them in condition any length of time. The following varieties are recommended for early, midseason and late:
Early.—Black Hamburg, Appley Towers, Madres- field Court, White Buckland Sweetwater, Foster Seedling, Royton Muscat.
Midseason house should be devoted wholly to Muscat of Alexandria, which is one of the finest of all indoor grapes. It thrives better in a compartment by itself, requiring a trifle more heat.
Late house.—Gros Colmar, Gros Maroc, Barbarossa or Gros Guillaume, Alicante, Diamond Jubilee, Prince of Wales, White Lady Hutt.
Many others may be added to the list, but these will be found to cover the season and varieties sufficiently for all purposes.
Forcing of peaches and nectarines.
These fruits come next in popularity to the grape and considerable space is devoted to their culture under glass. Great improvements have been brought about in recent years with both peaches and nectarines and a large number of new varieties are constantly appearing for forcing. One of the handsomest forcing peaches is Peregrine. The color is magnificent and flavor all that could be desired, with size sufficient to please the most exacting. Others might be mentioned to show the progress of time.
Cultural methods.
The same style of house that has been recommended for grape-culture will be found ideal for peaches and nectarines, although instead of having the walk down the center of the house, it is better along each side. This will allow planting the trees crosswise of the house on trellises about 6 feet apart, which affords ample space for a well-balanced tree. Also the same arrangements in regard to borders, drainage and so on should be carried out, although a slightly shallower border would be satisfactory. Prom 2 to 2 ½ feet of soil would be sufficient; nor is it necessary to make the border quite so rich for peaches and nectarines as for grapes, as the trees would have a tendency to rank growth, a condition that should be guarded against. Peach trees budded on plum stock are superior for forcing purposes. Choose the best trees obtainable for this work. In our climate, if everything goes well, the trees will grow into large proportions in three or four years. Therefore, space should be considered with this in view. A tree that is planted in such a way that the branches are evenly balanced on both sides, causing an equalization of the sap, will insure better results. Assuming the peach-house to be 25 feet in width with the trellis crosswise the house, allowing a walk on each side, each tree would have a spread of about 18 feet. One tree in the center of each trellis is sufficient, which allows ample room for development. If desired, a tree may be planted on each side of the permanent one for two or three years, but must be cut away as the space is needed for the permanent tree. Still another method may be adopted and probably the best, which is placing trees in tubs on each side, then as space is needed they may be moved away, whereas when planted in the border one is likely to leave them too long and crowd the main tree out of shape.
It would not be wise to force newly planted trees to any extent, but rather to bring them along gradually for the first season, when they will be in condition for forcing. If ripe fruit is in demand about the first week in May, the house must be started about the middle of December. The peach tree will come on and develop its blossoms in a comparatively moderate temperature and it would not be wise to submit it to extreme heat artificially. Peach trees delight in fresh air, and will resent a too close humid atmosphere. A temperature of 40° to 45° at night and 50° to 55° by day will suit their requirements at the start. Gradually increase this so that the temperature will range from 50° to 55° at night and 60° to 65° by day or 70° with sun heat when in bloom. After the fruit is set, another 5° may be added. Give plenty of air without lowering the temperature, particularly in cold weather. Give the house a light spraying two or three times a day when the weather is clear until they come into bloom. Do not spray while they are in blossom. After the fruit is set, spraying may be resorted to again once or twice a day according to weather conditions.
Peaches are subject to greenfly. As a precaution after the fruit is thoroughly set, syringe every ten days or so with a solution of whale-oil soap, enough just to color the water. This is an excellent remedy for both greenfly and red spider, both deadly enemies to peach foliage.
The peach tree will produce many more shoots than are needed to furnish the trellis, therefore the surplus will have to be removed. This is best done by degrees rather than removing them all at once, which would be likely to cause a check. A number of shoots may be pinched at the third leaf, which in all probability would form spurs or fruit-buds for the following season. The aim is to allow enough wood to remain to cover the trellis, but to avoid crowding. As the crop advances or before the fruit becomes of much size, thinning of the fruit would be in order. It is a serious mistake to overcrop. If a tree has a tendency to rank growth, a fairly heavy crop would be of advantage. The grower must be governed according to conditions.
Watering and feeding are important. Potash is necessary for all stone-fruits and should be applied in some form, or a complete fruit-fertilizer may be recommended. It is better to feed light and often rather than too much at once. Enough water must be supplied to give the border a thorough watering from top to bottom. Then no more should be given until necessary, for if the soil is not allowed to sweeten up it would be impossible to keep the trees healthy. It is not a good policy to have the trees or borders saturated just as the fruit is ripening. It is better to give them a watering a week or so in advance, which will usually last until the fruit is gathered. The object of this is to improve the flavor of the fruit.
One should not think that after gathering the fruit the house needs little or no attention. The temperature will not need close watching, but the fruit-buds have to form and develop, and good attention to watering and spraying the foliage is a wise step toward success for the following season. Cut away any useless wood after the crop of fruit has been picked, thus allowing the remainder of the wood to become well ripened. Well-ripened wood will withstand any reasonable amount of frost during the dormant state, and fruit-buds will respond when called upon with abundance of healthy strong blossoms. Winter-pruning may be done any time after the trees have cast their foliage. This means removing any weak growths, shortening back extremely strong growth and training the young wood so that it will spread over the space about 5 inches apart.
Varieties.
For forcing there are many varieties to choose from. The peach crop may be extended at least seven weeks for one house, but if the compartments are at command a season of five months or more may be had by planting early, midseason and late varieties. The following varieties may be relied upon for early, mid-season and late:
Early forcing peaches.—Duchess of Cornwall, Duke of York, Peregrine.
Early forcing nectarines.— Cardinal, Early Rivers, Advance, Lord Napier.
Midseason peaches. — Peregrine (Alexander, Noblesse), Bellegarde, Grosse Mignonne.
Midseason nectarines.—Stanwick - Elruge, Rivers, Orange- Chaucer.
Late-house peaches.— Crawford Late, Thomas Rivers, Princess of Wales.
Late-house nectarines.—Newton, Spencer, Humboldt, Victoria.
Numerous other varieties could be added to this list. However this will be found sufficient for all practical purposes.
Pot-fruits.
This method of producing fruit has found favor with many growers throughout the country, particularly in private establishments. It requires no specially built houses for the purpose, providing the house receives full sunlight with abundance of ventilation. There are two or three advantages of this concentrated method of growing: first, the house may be used for other growing crops after the fruit is gathered, as the trees may be placed outside or, as severe winter sets in, they may be stored away in a coolhouse close together until such time as they are needed for bringing into growth again; second, a large variety of fruits is adapted to this method of culture, such as peaches, nectarines, pears, plums, figs and the like. These trees may be grown into either pyramid or half-standard forms. Pyramids, as a whole, make a more attractive appearance in a house than any other form of training. A house for pot-fruits requires about the same treatment as that recommended for peaches planted in a permanent border. Care and watchfulness are required as to watering, particularly when first starting into growth, as at that stage there is not much foliage, consequently an over-abundance of water would have a tendency to sour the soil. Potting the trees is very important. There is no better time for this operation than early fall, or just as they are casting their foliage. Also a serious error is placing them in too large pots or tubs. They should be repotted every fall, but it is not always necessary to give them a larger tub. Often the ball may be reduced and placed into the same- sized tub. The soil should consist of a good fibrous loam used in a fairly rough state, if possible, as this will allow free action for the water to pass off. Firm potting is of great importance. Three parts of soil to one of thoroughly decayed rich manure with a little bone mixed in would be an excellent compost for the purpose. Careful watering after repotting is very important.
When the trees come into bloom, keep a fairly dry bracing atmosphere. Pears and plums will refuse to set their fruit otherwise. As the growth advances, frequent pinching or stopping the shoots should be attended to. Some growths will doubtless be much in advance of others. When the young growths reach the length of 5 or 6 inches, they should be pinched and again when they have extended another similar growth and so on. Usually in the case of pyramid trees, growth will be found more advanced at the top, hence those shoots should be stopped, resulting in more vigor for the lower branches.
Surface-dressing when the fruit is swelling is of great benefit. Either manure or a concentrated fertilizer may be mixed with the soil and added as a top-dressing, but by all means do not apply this until the fruit is swelling away freely.
Pot-fruit that has been properly cared for during the season of growth in regard to pinching and summer-pruning requires little winter-pruning aside from removing the very weakest growths.
Varieties.
The following varieties are the best:
Pears.—Souvenir du Congres, Madame Treyve, Hardy, Fondante d' Automne, Louise Bonne, Conference, Magnet, Pitmaston Duchess, Durondean, Princess.
Plums.—The Czar, Blue Rock, Oullins Golden, Early Transparent, Gage, Mallard, Denniston Superb, Belgian Purple, Golden Esperin, Transparent Gage, Green Gage, Grand Duke.
Figs.—Brown Turkey, Negro Largo, White Marseilles, Violet Seppr.
Apples and apricots also may be added, although they are not so profitable as the others mentioned.
Wm. Turner.
Forcing hardy plants.
Forcing is an economical method of securing large quantities of flowers in winter; it is extensively used by commercial florists for cut-flowers and flowering plants. Plants usually forced are hyacinths, tulips, narcissi and other Dutch bulbs, lily-of-the-valley, astilbe, dicentra, hybrid perpetual and rambler roses, Devtzia gracilis, hybrid rhododendrons (R. sinense) and Ghent azaleas, tender hydrangeas and lilacs.
This mode of procuring flowers at small cost has always been more or less in vogue among plantsmen, and of late years has received fresh impetus, owing to the heavy demands for decorative plants at Easter. It is not only an inexpensive method of getting flowers, but with most plants, after a little experience, the time of blooming can be easily calculated. The process has limitations, at any rate with our present knowledge of the matter, inasmuch as, with the exception of "retarded plants" and a few bulbs, it is not practicable in late autumn and early winter without the use of ether. It is possible, however, that by using "retarded plants," i.e., plants held over their natural time of flowering by keeping them in cold storage at a temperature sufficiently low to prevent growth, this difficulty may eventually be overcome. Except, however, with lily- of-the-valley, which is admirably adapted to this practice, little is known of the possibilities of this form of forcing; it is hoped that other plants, equally useful, may be treated in this way. It is evident that, on account of the cost of storage, bulky plants could not be handled.
The requirements for successful forcing are: (1) a good knowledge of the plants; (2) proper preparation; (3) a period of rest; and (4) proper care after the plants are brought into heat.
Those plants force most easily which bloom in and early summer. Late-blooming kinds, like Rhododendron maximum, clethra and Hydrangea paniculata var. grandiflora, do not give good results. No success is obtained with asters and goldenrod, unless they are retarded. These points must be studied out by the grower.
Trees and shrubs should be specially prepared for forcing by careful cultivation for one or two years before use. They can be planted out-of-doors, with plenty of room to develop, or they can be grown in pots, the latter method being used with vigorous plants, which are apt to run to growth without developing flower-buds. Close pruning is necessary, and root- pruning is helpful. Grafting, which has a tendency to dwarf and hasten maturity, is also used with strong growers. Sometimes both growing in pots and grafting are employed, as in lilacs.
A plant fit for forcing must be compact, both top and roots; economy in space is essential. It is now possible to secure from the French, Dutch and Belgian nurseries many plants grown for this purpose. A few come pot-grown, but most of them are from the open ground: very little of this work is done in American nurseries. Figs. 1553-1555 show the methods of preparing woody plants for forcing.
Herbaceous plants should be prepared for forcing with equal care, and the process may require several years. The removal of the flower-buds and growth, under high cultivation, in close, compact clumps, apparently produces the same results that pruning and grafting accomplish for trees and shrubs. Fig. 1556 shows the root-clump of an herb prepared for forcing.
Plants that have once been forced are commonly thrown away. It is generally cheaper to buy new stock, but lilacs, azaleas, and the like, can be planted out and will recover sufficient strength in two years for a second forcing, or for other use. Some species, like Viburnum plicatum, staphylea, and xanthoceras, if grown on in pots after forcing, may be again forced, and seem to do better the second year. This is probably explained by the fact that insufficient preparation was given for the first trial, the first forcing being really "proper preparation" for the second forcing.
Hardy plants must have a period of rest for successful forcing, the time required varying in different species. One cannot tell, except by experiment, that Paper White narcissi will force easily in November and December, while the double Von Sion will not; the individual equation of each kind is an element which must be considered. There is a popular notion that freezing will shorten the time for resting, or, at any rate, is conducive to the welfare of the plant. This idea does not seem to stand any practical test. After potting, do not subject the plants to severe frosts (10° to 12° F.), or else the roots, now much exposed, may suffer. The large buds of lilac and rhododendron may also be injured if frozen hard.
Pot the plants as soon as they ripen their growth in autumn, beginning in September with herbaceous stock, and continuing until severe frost. It is possible, but not desirable, to lift some things after the ground is frozen hard. Plants received from abroad are potted on arrival, or, if furnished with a ball like azaleas (Fig. 1553), they can be stored and not potted until brought into heat. Dutch bulbs are boxed or potted as they are received, and buried in the earth or piled in stacks and covered with enough leaves and litter to exclude frosts. Lily-of-the- valley, astilbe and dicentra may be kept in their packing-cases in a cool pit until ready for use. Large plants in tubs and boxes can be covered with leaves and kept out-of-doors, but most plants should be stored in a cool cellar, pit or frame kept at a temperature of 35 F.; a temporary variation of 5° either way does no harm. It is well to delay this storage until as late in the season as possible, but it must be done before severe weather. Plants may be stowed compactly in several tiers if necessary. It must be remembered that no growth is to be allowed while stored; it is their period of rest, and this must be enforced. Good ventilation must be given on bright days and every precaution taken against an accumulation of moisture: if the plants are well watered when put away very little will be required afterwards. Dampness is most serious with evergreens, like kalmia, and such things as Phlox subulata. This stock should have the airiest positions; sometimes it can be placed in shallow frames 2 feet deep, which are drier than deep pits. In severe weather the pits are often covered with snow a week or more, but the plants will not suffer if this happens but once or twice during the winter. At such times mice and squirrels will make trouble unless trapped or poisoned.
Nothing except retarded plants, a few bulbs and one or two kinds of prunus should be brought in before November. December 15 to January 1 is as early as it is safe to begin forcing most hardy plants; it will be found that as the days lengthen the results will be more satisfactory. At first the plants must be kept cool, 45° F., or thereabout. Syringe twice a day until the buds swell: after growth starts the treatment is the same as that given greenhouse plants, and they can be put in a much warmer house if so desired. It is at this time that care in handling, particularly in the matter of heat, makes it possible to time the period of blooming so accurately, but it is impossible to give any general rules satisfactorily to cover these matters.
A few plants, like lily-of-the-valley, can be placed directly in a forcing-box, generally made over the pipes in the hottest house, where a temperature of 80° or more can be maintained. They are first soaked in water for a day or two and then kept in this heavy heat until flower-buds are well developed (Fig. 1557).
Tulips, hyacinths and other bulbs, sometimes an azalea or lilac, can also be hurried up in such a box, but it is dangerous, and not good practice; better and more lasting flowers come with ordinary treatment. Trilliums (Fig. 1558) and various early-flowering wild plants may be forced with satisfaction.
Although no rules can be given for the time required in forcing, it is knowledge not hard to acquire with even surprising exactness. Nothing is likely to require more than three months in houses ranging from 45° to 55° F.—i.e., after bringing in from the pits. A month or six weeks is good time to allow in February and March, but with the same plants and temperatures, more time would be needed earlier; with the advance of the season, the work is quicker and less uncertain. There is a great difference in plants. Rhododendrons (the hybrids) require eight weeks or more, but one species will often bloom in March, within twenty-four hours. Plants like the rose, which must make a growth before the buds form, take more time than Rhododendron sinense. The difference between dull and bright weather is an important factor, but with extra firing, or the use of the forcing-box, these matters even up, and the average time of flowering is wonderfully even. In this work, a man with good plant sense is most likely to succeed.
The use of anesthetics in forcing.
In the latter part of the last century and early in the present, experiments were begun in Germany, and confirmed in France, England and the United States, in subjecting plants to the influence of ether and chloroform for the purpose of securing better results in forcing. Ether seems, for many reasons, the most practical agent, but, owing to its cost and the extra expense of handling the plants, this process does not appear to be in common use among florists. For a detailed treatment of this subject, the reader is referred to an article by M. Emile Lemoine in the Journal of the Royal Horticultural Society (London), Vol. XXVIII, 1903-4, p. 45. See, also, the article Etherization, p. 1146, Vol. II.
In the main, the treatment of plants for this purpose is as follows: A container, which can be hermetically sealed and of the proper size is provided. In it are placed the plants "as dry as possible, in equally dry sand." The temperature of the box is 62° to 65° F. Under the lid is a vessel into which the ether can be poured and the hole sealed at once. It is important to have the ether at the top as its vapor is heavier than air and consequently gravitates downward. Ether, particularly when mixed with air, is very inflammable and lighted matches, cigars or pipes must be kept away. "Thirty or forty grammes of ether are enough for one hundred cubic litres of air: one gramme equals fifteen and one-half grains, one litre equals sixty-one cubic inches." The ether used is "pure sulfuric ether which boils at 95° F." The plants are kept under the influence of the ether for two days; sometimes they are removed for two days and the etherization repeated for the same length of time. Afterwards they are placed in a coldhouse and "treated in the usual manner." Lilacs "were in full flower eighteen days after being placed in the greenhouse," one, "Marie Legraye still earlier." Johannsen made lilacs "flower regularly" the first two weeks in September which had been etherized the first week in August." With other shrubs, such as Rhododendron sinense (Azalea mains'). Viburnum opulus, Primus triloba, Deuteia gracilis ana some of the spireas, the results were more or less favorable."
Trials with chloroform apparently have been less successful and other anesthetics and stimulants have been found failures.
B.M. Watson.
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== References ==
== References ==
*[[Standard Cyclopedia of Horticulture]], by L. H. Bailey, MacMillan Co., 1963 <!--- xxxxx *Flora: The Gardener's Bible, by Sean Hogan. Global Book Publishing, 2003. ISBN 0881925381 --> <!--- xxxxx *American Horticultural Society: A-Z Encyclopedia of Garden Plants, by Christopher Brickell, Judith D. Zuk. 1996. ISBN 0789419432 --> <!--- xxxxx *Sunset National Garden Book. Sunset Books, Inc., 1997. ISBN 0376038608 -->
*[[Standard Cyclopedia of Horticulture]], by L. H. Bailey, MacMillan Co., 1963
<!--- xxxxx *Flora: The Gardener's Bible, by Sean Hogan. Global Book Publishing, 2003. ISBN 0881925381 -->
<!--- xxxxx *American Horticultural Society: A-Z Encyclopedia of Garden Plants, by Christopher Brickell, Judith D. Zuk. 1996. ISBN 0789419432 -->
<!--- xxxxx *Sunset National Garden Book. Sunset Books, Inc., 1997. ISBN 0376038608 -->
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