GERANIUM, the name of a genus of plants, which is taken by botanists as the type of the natural order Geraniaceae. The name, as a scientific appellation, has a much more restricted application than when taken in its popular sense. Formerly the genus Geranium was almost conterminous with the order Geraniaceae. Then as now the geranium was very popular as a garden plant, and the species included in the original genus became widely known under that name, which has more or less clung to them ever since, in spite of scientific changes which have removed the large number of them to the genus Pelargonium. This result has been probably brought about in some degree by an error of the nurserymen, who seem in many cases to have acted on the conclusion that the group commonly known as Scarlet Geraniums were really geraniums and not pelargoniums, and were in consequence inserted under the former name in their trade catalogues. In fact it may be said that, from a popular point of view, the pelargoniums of the botanist are still better known as geraniums than are the geraniums themselves, but the term "zonal Pelargonium" is gradually making its way amongst the masses.
The species of Geranium consist mostly of herbs, of annual or perennial duration, dispersed throughout the temperate regions of the world. They number about 160, and bear a considerable family resemblance. The leaves are for the most part palmately-lobed, and the flowers are regular, consisting of five sepals, five imbricating petals, alternating with five glandules at their base, ten stamens and a beaked ovary. Eleven species are natives of the British Isles and are popularly known as crane's-bill. G. Robertianum is herb-Robert, a common plant in hedgebanks. G. sanguineum, with flowers a deep rose colour, is often grown in borders, as are also the double-flowered varieties of G. pratense. Many others of exotic origin form handsome border plants in our gardens of hardy perennials; amongst these G. armenum, G. Endressi, G. ibericum and its variety platypetalum are conspicuous.
From these regular-flowered herbs, with which they had been mixed up by the earlier botanists, the French botanist L'Heritier in 1787 separated those plants which have since borne the name of Pelargonium, and which, though agreeing with them in certain points of structure, differ in others which are admitted to be of generic value. One obvious distinction of Pelargonium is that the flowers are irregular, the two petals which stand uppermost being different - larger, smaller or differently marked - from the other three, which latter are occasionally wanting. This difference of irregularity the modern florist has done very much to annul, for the increased size given to the flowers by high breeding has usually been accompanied by the enlargement of the smaller petals, so that a very near approach to regularity has been in some cases attained. Another well-marked difference, however, remains in Pelargonium: the back or dorsal sepal has a hollow spur, which spur is adnate, i.e. joined for its whole length with the flower-stalk; while in Geranium there is no spur. This peculiarity is best seen by cutting clean through the flower-stalk just behind the flower, when in Pelargonium there will be seen the hollow tube of the spur, which in the case of Geranium will not be found, but the stalk will appear as a solid mass. There are other characters which support those already pointed out, such as the absence of the glandules, and the declination of the stamens; but the features already described offer the most ready and obvious distinctions.
To recapitulate, the geraniums properly so-called are regular-flowered herbs with the flower-stalks solid, while many geraniums falsely so-called in popular language are really pelargoniums, and may be distinguished by their irregular flowers and hollow flower-stalks. In a great majority of cases too, the pelargoniums so commonly met with in greenhouses and summer parterres are of shrubby or sub-shrubby habit.
The various races of pelargoniums have sprung from the intermixture of some of the species obtained from the Cape. The older show-flowered varieties have been gradually acquired through a long series of years. The fancy varieties, as well as the French spotted varieties and the market type, have been evolved from them. The zonal or bedding race, on the other hand, has been more recently perfected; they are supposed to have arisen from hybrids between Pelargonium inquinans and P. zonale. In all the sections the varieties are of a highly ornamental character, but for general cultivation the market type is preferable for indoor purposes, while the zonals are effective either in the greenhouse or flower garden. Some of the Cape species are still in cultivation - the leaves of many of them being beautifully subdivided, almost fern-like in character, and some of them are deliciously scented; P. quercifolium is the oak-leaf geranium. The ivy-leaf geranium, derived from P. peltatum, has given rise to an important class of both double- and single-flowered forms adapted especially for pot culture, hanging baskets, window boxes and the greenhouse. Of late years the ivy-leaf "geraniums" have been crossed with the "zonals," and a new race is being gradually evolved from these two distinct groups.
The best soil for pelargoniums is a mellow fibrous loam with good well-rotted stable manure or leaf-mould in about the proportion of one-fifth; when used it should not be sifted, but pulled to pieces by the hand, and as much sand should be added as will allow the water to pass freely through it. The large-flowered and fancy kinds cannot bear so much water as most soft-wooded plants, and the latter should have a rather lighter soil.
All the pelargoniums are readily increased by cuttings made from the shoots when the plants are headed down after flowering, or in the spring, when they will root freely in a temperature of 65° to 70°. They must not be kept too close, and must be very moderately watered. When rooted they may be moved into well-drained 3-in. pots, and when from 6 to 8 in. high, should have the points pinched out in order to induce them to push out several shoots nearer the base. These shoots are, when long enough, to be trained in a horizontal direction; and when they have made three joints they should have the points again pinched out. These early-struck plants will be ready for shifting into 6-in. pots by the autumn, and should still be trained outwards. The show varieties after flowering should be set out of doors in a sunny spot to ripen their wood, and should only get water enough to keep them from flagging. In the course of two or three weeks they will be ready to cut back within two joints of where these were last stopped, when they should be placed in a frame or pit, and kept close and dry until they have broken. When they have pushed an inch or so, turn them out of their pots, shake off the old soil, trim the straggling roots, and repot them firmly in smaller pots if practicable; keep them near the light, and as the shoots grow continue to train them outwardly. They require to be kept in a light house, and to be set well up to the glass; the night temperature should range about 45°; and air should be given on all mild days, but no cold currents allowed, nor more water than is necessary to keep the soil from getting parched. The young shoots should be topped about the end of October, and when they have grown an inch or two beyond this, they may be shifted into 7-in. pots for flowering. The shoots must be kept tied out so as to be fully exposed to the light. If required to flower early they should not be stopped again; if not until June they may be stopped in February.
The zonal varieties, which are almost continuous bloomers, are of much value as decorative subjects; they seldom require much pruning after the first stopping. For winter flowering, young plants should be raised from cuttings about March, and grown on during the summer, but should not be allowed to flower. When blossoms are required, they should be placed close up to the glass in a light house with a temperature of 65°, only just as much water being given as will keep them growing. For bedding purposes the zonal varieties are best struck towards the middle of August in the open air, taken up and potted or planted in boxes as soon as struck, and preserved in frames or in the greenhouse during winter.
The fancy varieties root best early in spring from the half-ripened shoots; they are slower growers, and rather more delicate in constitution than the zonal varieties, and very impatient of excess of water at the root.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)