This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
A very handsome order of plants, and mainly herbaceous, though not all hardy. Gentiana is the principal genus, and the type of the order. In it there are some of the most beautiful and brilliant of hardy subjects, over which the true lover of plants becomes enthusiastic, and regards as his horticultural gods. The same may be said of Spigelia, of which only one species is occasionally observed in cultivation: a lovely plant, but always difficult to keep, and requiring too peculiar conditions, perhaps, ever to become popular; for without peculiar treatment it refuses to yield its charms, or live for any length of time. Menyanthes and Limnanthemum or Villarsia are the only two other genera in the order that, besides Gentian and Wormgrass, yield hardy ornamental subjects. These are both aquatic plants, and each furnishes only one species known at present to cultivation out of doors. They are handsome plants, adapted to ornament the margins of ponds or lakes, or other still shallow waters, and both are found in greater or less frequency in the natural lakes or ponds of Britain and Ireland, though not so often in those that are artificial as might be expected, considering their great beauty, elegance, and fragrance.
A very lovely plant, familiar in most gardens. It is so well known that description would be superfluous; and its uses as an edging plant for walks, beds, or alleys, and for planting in masses upon banks or in rounded slightly-raised patches in the mixed border or on rockwork, and its brilliant beauty in any or all of these positions, are too well known and appreciated to need remark or recommendation. It has long been a favourite with cottage and amateur gardeners, and it is one of those gems that should be in every garden - it is so easily cultivated, and does so very generally well in all parts of the country. Yet accusations of fastidiousness, as regards soil and situation, have been brought against it often, and, as I think, undeservedly. I have seen the plant in every imaginable aspect and position, and in a great variety of soils, and very generally doing well. But it has likes and dislikes - and very few plants that I know have a better right to protest in its own way against ill-usage; they do not, however, amount to fastidiousness.
It dislikes two extremes of soil - brick, clay, and sand; and it likes solidity, depth, moisture, the latter especially during late spring and early summer, when it is making its growth, but at all times perfect drainage is also liked; and if these very ordinary and reasonable conditions are attended to, the plant will amply reward in April, May, and June by the brilliancy and profusion of its deep-blue flowers. I would repeat that solidity of soil is of the utmost importance to success with this, as with every, Gentian; and deep moist loam it likes best. There is a variety having the tips of the segments of the corolla coloured greenish white; as a novelty it has some merit, but for simple decoration it is inferior in effect to the normal blue. The plant is a native of mountain pastures in many parts of Europe.
One of the most accommodating of Gentians. A native of bushy pastures on the Alps, the Vosges, and Apennines. It grows 1 foot or 2 feet high, erect and graceful; the stems are well clothed with stalkless egg-shaped leaves, narrowing much towards the point, and distinctly five-veined. The flowers are produced in rather close spikes, usually in pairs, and almost stalkless, and are deep purplish blue. A free-flowering handsome border-plant, succeeding best in deep rich sandy loam. There is a fine white-flowered variety which is equally easy to cultivate, and both may be used on rockwork, only it must be remembered that the soil should be deep and moist.
Unlike the two last and the majority of Gentians, this species has the corolla divided into four instead of five segments, giving the appearance of a cross when open, hence the significance of the name; but it is farther descriptive of the arrangement of the leaves, which are rather closely packed in four rows along the stems. The flowers are deep blue, arranged in whorls or clusters in the axils at the upper ends of the stems. Height about 9 inches or 1 foot. Flowers in June and July. Native of dry mountain-pastures on the great ranges of central and southern Europe. May be cultivated without much difficulty in any moderately good garden loam in the open border or rockwork, and is handsome and distinct.
A very beautiful species growing about 1 foot high, with rather diffuse stems and lance-shaped leaves. The flowers are bright pale blue, rather openly bell-shaped, produced in clusters in the axils of the upper leaves, appearing in June and July. Native of Siberia. Succeeds well in border or on rock-work in moist peaty loam, sandy and well drained.
The roots of this species supply the greater bulk of bitter Gentian of the druggists. It is the largest and most bulky of the Gentians known to cultivation, reaching the height of 3 or 4 feet, with erect strong stems. The leaves are broadly egg-shaped, and ample. The flowers are produced in dense whorls in the upper part of the stems, the full inflorescence having the appearance of a long whorled spike; they are yellow, and appear in June and July. Native of high mountain-meadows in central and southern Europe. It is a striking border-plant, both on account of the broad ample leaves and the inflorescence, which, though not so showy in colour as that of many, is very distinct. Very deep, rich, moist loam suits it best.
A British species, though not common. It grows about 9 inches or 1 foot high. The leaves are oblong, lance-shaped. Flowers long, deep blue, lined on the outside with green, produced in the axils in the upper part of the stems, and appearing in August and September. Flourishes best in rich, peaty, sandy loam, moist, but well drained, and succeeds in either border or rockwork. It is a very common plant in moist pastures in hilly countries throughout Europe and Northern Asia.
A strong-growing plant about 2 feet high, with erect strong stems. The leaves are oval, on short stalks. The flowers are produced in clusters at the extremities of the stems, and are pale yellow, spotted with purple. Flowers in June and July. The plant is a native of high alpine pastures on the great mountain-ranges of Europe. It succeeds well in the mixed border in deep sandy loam.
This is one of the high alpine species. It grows only a few inches high, with branching spreading stems. The leaves are narrow, lance-shaped. The flowers are deep blue, divided into ten segments, each alternate one being smaller and more angular than the principal or representative five. They appear in June and July. Native of lofty stations on the Pyrenees.
A good and accommodating border plant, growing 1 or 2 feet high. The stems are ascending, and clothed with broadly lance-shaped leaves. The flowers are stalkless, in rather close heads at the extremities of the stems; they are blue and barrel-shaped, being almost closed at the mouth, which is cut into ten nearly equal segments. They appear in August and September. Native of N. America. This is one of the most easily cultivated species, thriving in any ordinary garden soil.
A very handsome species, suitable only for culture on rockwork, except where moist peaty borders exist, when it may be successfully grown on the level; but it delights most in peat, or sandy loam and peat, whatsoever station it may occupy. The plant forms tufts about 9 inches high. The leaves are lance-shaped, rather broadly so, and distinctly three-veined. The flowers are large, bright blue, with a white-and-blue spotted throat, and the smaller alternate segments are finely cut. Flowers in August and September. Native of the Caucasus.
One of the smallest and most beautiful of Gentians. It grows only an inch or two high, and has the same close matting style of growth as Gentianaceae acaulis, but is even more dense and compact than that plant. The leaves are hard, small, and oblong in shape. The flowers are borne on short stems often barely carrying the whole length of the tube of the flower above the mat of leaves; they are funnel-shaped, and divided at the mouth in five spreading rather broad lobes, having intermediate and smaller lobes slightly cut or crested between. They appear in April and May. The plant is a native of high alpine pastures, and is often coddled and vexed to death in cultivation. Although a tiny plant, it requires a deep, rich, cool, sandy loam to grow in, and a good open exposure, and, like all or nearly all Gentians, water in abundance is necessary during the growing season. The rockwork is the best place for it, where, if the natural soil is not what it flourishes best in, a suitable compost may be provided for it; but if suitable, it may be tried with every confidence in the open border.