HALF-HARDY HERBACEOUS PERENNIALS
So far we have treated only of the hardy perennials which can be grown in the open border all through the year. Our gardens would be much poorer, however, if we could not rely on a considerable number of showy flowered plants of somewhat tender nature. It is difficult to imagine our parks and open spaces bereft of all the Geraniums,, Calceolarias and similar perennial bedding plants. Practically all of these are of course grown in pots in the greenhouse, for indoor decorations, but they are for the most part brought into the open garden to colour the beds and border during the safe summer months, that is, from June to September.
Possibly every one of these subjects requires slightly different treatment; but, in general terms, we can outline their cultivation, and the amateur who owns a greenhouse will soon discover for himself those tricks of the trade which make all the difference between a mediocre garden and one of first quality. Roughly speaking, we can divide these tender perennials into two groups: those with bulbous or tuberous roots, and those with fibrous root-stocks.
Such plants as the tuberous-rooted Begonias and Cannas are treated in very much the same way as are; that is to say the fleshy roots are started into growth in heat and moist , in February or March. By the end of May, or the first week in June, the plants, which have by this time been potted up singly, are ready for setting out in beds, in serried ranks in the formal garden, or in groups in the mixed border.
In the autumn when the leaves have died down, the roots are lifted, cleaned and stored in dry soil or sand in a shed, or under the shelves of the cold greenhouse, until the following spring. Increase of such plants is by division of the root-stocks, removal of young shoots to root assoon after the new growth commences, or in the more natural way by seed. Seeds of bulbous-rooted plants are, generally speaking, rather long in reaching maturity, and the root division, or propagation by cuttings, is the common practice.
Fibrous-rooted perennials of tender character and such shrubs as the Calceolaria, the Zonal, which most amateurs call Geranium (both these are shrubby in character if they are allowed to continue growth normally), are also grown outdoors in the summer months and under glass in winter. In this case, however, the roots are not usually dried entirely during the winter months, but remain in the pots. Water is given very sparingly, so that the plants remain dormant, and in early spring an increase of warmth and moisture encourages them to put out fresh shoots.
Uniformity in Size
Chiefly because the gardener desires, for formal bedding schemes, plants of similar height that will come into flower at the same time, the practice has arisen ofeach season, and using only these new plants for June bedding. A plant which is set out in June, and flowers during the summer months, will be found by, say, the end of August or beginning of September to have produced, in addition to flower-heads, a number of new side shoots which are at that time in a half-matured condition. These side shoots are ideal for cuttings. They can be taken off and inserted immediately, in sandy soil, in a propagating frame. The majority of such plants can be increased in this manner even without the assistance of a propagating frame, since most cuttings if inserted in sandy soil in a shady part of the open garden, will root in late summer.
Cuttings rooted in August will be ready to pot up for the winter before the severe frosts arrive, and the young plants can be wintered in any greenhouse where it is possible to exclude actual frost.
Certain shrubs such as the autumn floweringare frequently used for bedding schemes. It is not always necessary or desirable to take cuttings annually. Sometimes quite large pot plants are merely sunk below the soil level during the summer bedding season in order to produce fine effects, the pot being brought indoors again at the approach of frost.