The departments of a garden are to some extent interwoven, and on occasion a subject which belongs to the open air finds its way into the greenhouse. This is particularly the case with certain shrubs, and one has only to mention the Rose to present a shining example.
With the increased attention which is given to hardy plants in these days, there is less disposition on the part of many to go in for glass, nevertheless, there may be some readers who are not only shrub-lovers, but have greenhouses and conservatories to furnish. Can they draw on the resources of their shrubberies with advantage at any period of the year?
The reply is that many shrubs may be lifted from the open ground and forced into early bloom under glass. Moreover, they will suffer no injury in the process; provided that the simple precaution is taken of giving them a brief interregnum in a cool house before returning them to the open ground. If a shrub were put direct out of a warm house into the open air it might be injured, however nominally hardy it might be, in a spell of cold weather.
There could be no more convincing proof of the value of shrubs and trees for indoor decoration than the groups in pots and tubs which are set up at late winter and early spring flower shows. The exhibits begin in February; they grow more numerous in March; in April they are abundant. One sees many members of the great genus Prunus, including Almonds, Apricots, Cherries and Peaches. There are Pyruses, notably, perhaps, Scheideckeri. Lilacs are prominent. Tree Paeonies are represented. There are Azaleas and Rhododendrons in rich variety. Magnolias are seen. And there are less important but still beautiful things: Wistarias, Spiraeas, Deutzias, Ribes, Laburnums, Ceanothuses, Viburnum^, Thorns, Japanese Maples, Amelanchiers, Staphyleas, Forsythias, and Kerrias.
The forcing of shrubs and trees may be either casual or systematic. It may consist of merely taking up a few things from the borders, a choice being made where the plants are getting crowded, and planting them out again in a fresh place after forcing; or it may consist in setting apart a certain number of plants specially for forcing purposes, treating them at all periods of the year for the one particular purpose. Plants so grown will not be kept under glass the whole year; they will be outside part of the time, but they will have special quarters.
It is particularly trade growers who cultivate shrubs systematically for forcing, but some owners of large gardens do it with the help of their staff of trained gardeners. With respect to smaller private places, it would probably be hardly worth while; but that is a matter for individual judgment. The systematic forcing of shrubs and trees is not a light and cheap process. Large pots, a considerable quantity of suitable soil, a reserve ground and a not inconsiderable amount of labour are called for. These things arise out of the size of the various plants. Shrubs and trees are bigger things than Primulas and Cyclamens, thus they call for larger pots. With larger pots more soil, more space and more labour are required. There is also the question of pruning to consider.
The issue once freely and fairly stated, we may go on with a clear conscience to point out the great beauty of certain shrubs and trees when forced into bloom in winter and early spring. The most beautiful of all, perhaps, are the double Peaches, of which a typical variety is Clara Meyer, with its lovely pink flowers that stud the branches closely. This can be had in bloom in March. The double variety of Pyrus spectabilis is another delightful subject, and makes a charming companion for Scheideckeri. Both of these can be flowered in March, several weeks in advance of their natural season in the open air.
Lilacs are among the greatest favourites, because apart from their beauty and perfume they force well. The modern forms such as Marie Legraye, single white; Maréchal de Bassompierre, double reddish lilac; Arthur W. Paul, double red; Alba grandiflora, single white; Madame Lemoine, double white; Souvenir de Louis Spath, deep brownish red, single; Miss Willmott, double white; President Carnot, double lilac; Grand Duc Constantin, double soft lilac; and La Ville de Troyes, purplish red single; are beautiful. The old variety Charles X., with purplish red single flowers, that come white when it is forced in the dark, should also be mentioned, as it is cheap and forces well. These are all varieties of the common Lilac, Syringa vulgaris; but the Persian Lilac also forces well. Lilacs grown for forcing are kept to about four shoots, all side growths being removed at an early stage. The routine for early winter bloom is to plant out in rows, in spring, disbud as required throughout the summer, chop round the plants in August, lift and pot in September, force in a dark, hot place, harden after flowering, plant out again, give a year's rest and repeat the forcing a second season. To force into bloom in late winter or early spring is a much simpler process, as only gentle warmth is required and the plants may be grown in a light house with other subjects.
For steady forcing to give bloom in late winter and early spring, Lilacs and other shrubs and trees need not be put in heat until the New Year, and then they should only have a mild warmth of about 50° for the first two or three weeks. After that, if convenient, 55° to 6o° may be allowed. If greater heat than this is given, the bloom will be earlier, but it will not last so long, unless indeed, there is a second and cooler house into which the plants can be shifted when they come into flower. There is the further objection to hard forcing that a greater strain is put on the plants. A moist atmosphere, induced by syringing, is desirable while the plants are swelling their buds, but a drier air is desirable when the bloom opens.
After flowering, the wood which has bloomed should be removed, and about half a dozen new branches allowed to develop. With a limited number, the wood will ripen well and there will be good bloom the following year. This applies to most of the deciduous flowering shrubs. Evergreen Rhododendrons will not, of course, be cut back in this way. If the plants have to be put out before the middle of May they should be stood in a sheltered place, where they will not be subjected to late frosts and cold winds.