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.
There are purple, blue, and white Delphiniums, both species and varieties quite numerous in cultivation, but till the present interesting and striking species was introduced last year by Mr Thompson of Ipswich, we could not count scarlet in the list of colours offered by the family. About fourteen years ago D. cardinale was introduced as a scarlet species, and great expectations were formed of its character from the name and description that accompanied it. It was red, but a bad red; and it proved, besides, a very intractable subject in cultivation, choosing rather to die after the manner of biennials, than live when its abortive attempt at flowering was over. The present plant is a very different one in every respect, and I have no hesitation in saying it is one of the greatest acquisitions that have been made to the list of hardy perennial flowers of late years. I cannot speak positively of it as being hardy, however, though it may be assumed, from the fact of its being a native of California, as well as from the way in which it withstood the wintry weather of last May, that it will stand uninjured in winter when fairly at rest in this country. Our plant was received in April from Mr Thompson, and was a very healthy one in a 4-inch pot.
It was planted out in the first week in May, and was left unprotected, but started into growth at once; and on the 16th, when flower - stems were beginning to come away vigorously, it stood the test of 10° of frost without the least injury, while herbaceous Paeonies and many other hardy herbaceous plants had every bit of fresh growth more or less injured. It has flowered profusely, and still continues to flower, with promise of many spikes to come. It is earlier and more continuous in its habit of flowering than any Delphinium I am acquainted with. It is a vigorous-growing freely-branching plant, about 2 feet in height, with me; but I observe that Mr Thompson, in speaking of it in his catalogue, remarks that in this and other respects it is apt to vary from seed. The leaves are mostly radical, those on the stem being mainly confined to the points where the branches divide; they are three-lobed, dark green, thick, and fleshy, and have a light grey-green spot at the base of each lobe. The stems are quite smooth, and without any covering, as the name implies, but have a purplish tinge below, and become glaucous towards their points. The flower-spikes are loose, each flower being supported on long stout peduncles.
The flowers are 1½ inch (in length, the spur itself being about 1 inch long and somewhat hooked at the end. They are bright scarlet, and the sepals are tipped with a spot of brownish green.