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.
This is rather a numerous group, composed of a few annual and biennial, and a majority of perennial species. The perennials are half-shrubby plants of humble growth, and evergreen to a greater or less degree; the flowers are small individually, but produced in dense masses and in long succession. They are plants of the easiest culture, succeeding best in light gritty loam of a rich quality, but doing very well in a great variety of soils and situations. The rockwork, mixed border, and borders of shrubberies are all fit places for these plants, and some are qualified for naturalising, and will be noticed in their place. They are propagated by division in autumn and throughout winter and spring, but if done in early autumn there is no sacrifice of bloom, which is inevitable to some extent in the later periods; by cuttings also in spring and throughout the summer, inserted in sandy loam and leaf-mould under a hand or bell glass in a shady place, as behind a low wall or hedge. Cuttings, if early struck, make the most vigorous plants, and flower the strongest the following year, and a few should be struck annually in order to keep up a healthy and ample stock.
This is especially necessary where they are to be largely used in filling up the beds of the summer flower-garden in the spring months; and stock of neat uniform plants can only be maintained by this means. In this case cuttings may be taken to the extent required immediately before the summer occupants claim their quarters, and the old plants be turned on the rubbish-heap, or utilised in any other way.
This is a compact-growing species, with small oblong leaves, broader at the point than base, silvery on the under-side, and dotted above with minute starry grey hairs. Flowers in dense panicles, yellow, appearing in April and May; native of Piedmont and Corsica, in exposed rocky places. Best fitted for culture in rockwork, and succeeds but indifferently in the open ground, where the soil is naturally moist: height 9 inches to 1 foot.
This is a splendid sort, of shrubby diffuse habit, with large lanceolate leaves, hoary on both surfaces, the margin marked with a few obscure teeth. The flowers are produced in great profusion in April, May, and June, and are very conspicuous in masses at a distance, being bright golden yellow. This is the most valuable of all the spring yellow bedding plants, being superior to the ordinary form of Alyssum saxatile in vigour, colour, and profusion of bloom. It grows well everywhere, and in a variety of soils, and is quite hardy, but prefers light dry loam. Where the ground is wet, little hillocks should be raised to plant upon, in order to secure immunity from the effects of stagnation. It may be naturalised on dry banks in semi-wild places with ease, if rabbits do not abound in the place; but need not be attempted if they do, as they are partial to the plant in a strong degree.
Botanists are not at one with each other regarding the distinctness of this plant from Alyssum gemonense, and the strongest opinion appears to be favourable to regarding the latter as a variety of the Rock-Madwort. The two forms are, however, quite distinct for horticultural purposes in large collections, but in smaller only one may be recommended; and in that case Alyssum gemonense should be preferred, as being the most beautiful, and adaptable to a greater variety of uses. Alyssum saxatile is, however, equally well fitted for naturalising on dry banks and about the walls of ruins, where a little soil may be introduced for it to grow in. Height about 9 inches. Native of many countries of S. Europe and W. Asia. Flowers about the same time as Alyssum gemonense. A variegated form of this species may or may not be considered valuable, according as taste in these things sways one. My own opinion is that it is worthless; the contrast between the hoary ground-colour and the creamy-white margins is not sufficiently distinct; and the variegation has the effect also of depreciating the beauty of the flowers, which is very obvious when the two sorts are grown side by side.