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 interesting and attractive genus, of few species so called, but which are not strikingly distinct in character one from the other. They are all, however, worthy of cultivation, though not together in one collection, except perhaps in the largest; but no collection of spring flowers may be considered complete without one or other of their best forms in its ranks. The same spreading trailing manner of growth, and the same rosette style or crowding of the leaves at the extremities of the stems and branches, as characterise the Rock-Cresses of the Albida type, are characteristic of these little plants, but in miniature only, the plants being less vigorous and bold, and when managed well in a congenial situation and soil they become most beautiful objects. They are best adapted for culture on rock-work, their low carpet-like growth being invaluable for that kind of ornamentation. They succeed in all light loams freely in any situation, but very indifferently, and often fail entirely, in heavy wet soils. In beds and borders, in soils of the unfavourable kinds, it should be raised above the surface-level by some means, so as to secure that comparative dryness and freedom from stagnation it likes so well.
A very good plan, in heavy loam and clay, is to make a pit to the extent the plant is designed to occupy, and about half the depth of a spade, in with stones, brick-rubbish, or rough charcoal to the surface level, finishing up with a mound of good loam and leaf-mould on the top of the drainage, about 6 inches deep, on which to plant. The better forms of these plants are worth any amount of trouble that may be necessary to secure their wellbeing, and those who succeed will not regret any tax that may have been temporarily laid upon them, when they come to enjoy the rich beauty they so freely and continuously yield at a period of the year when flowers in profusion are comparatively rare. Their brilliant dense masses of flowers are being turned to excellent account in spring bedding, or massing of flower-gardens. Propagation may be effected by cuttings in early summer in a shady place, by division in autumn or early winter, and by seeds sown as soon as ripe in a cold frame or under a hand-glass, the plants to be pricked carefully off into rich light soil as soon as they can be handled.
This is comparatively a new form, and is probably of garden origin. It is the most brilliant of the group, forming dense carpet-like patches of pale-green foliage, which is profusely covered with comparatively large light violet-purple flowers from March till June.
This is an old inhabitant of gardens, and though decidedly inferior in showy qualities to the preceding and other varieties, is no mean plant in its season. It is less luxuriant than Campbell's Aubrietia, and the flowers are smaller and pale purplish blue, but very abundant, appearing about the same time. The varieties Aubrietia Deltoidea Grandiflora and Aubrietia Deltoidea Graeca are distinguished only by greater size and brilliancy of colouring, and are simply more valuable where these qualities are essential in the highest degree. They are all valuable plants for town gardens, for, except that their natural brightness does not appear to the greatest advantage in a smoky atmosphere and amid smutty surroundings, there are few Alpine plants that can accommodate themselves with more facility to conditions so opposite to those of their native homes. Aubrietia deltoidea is a native of the Levant.
Aubrietia, in some variety as regards the size of the leaves and vigour of growth, and somewhat also in the particular shades of green which the several forms present, are very neat pretty plants with their leaves arranged rosette fashion. They are of spreading, yet close-carpeting habit, and when well attended to in the matter of trimming and equalising their growth during the growing season, they make a very pleasing soft carpet of green. These are favourite plants with many for spring bedding, and are very beautiful for three months in favourable weather, clothed as they are during that period in the beautiful purple and deep lavender flowers that they severally present. This is a consideration that may be objectionable in the flower-garden in the way in which I wish to recommend these and other subjects of similar character, except it be utilised by placing next to it something that would contrast or harmonise with it in its flowering season, which is often prolonged into June, and therefore into the earlier part of the summer display.
The variegated form of A. deltoidea is one of the most attractive of minute variegated plants at all times, and is particularly beautiful when in flower.