Some plants resolutely refuse to be ‘improved’ and others seem purpose-built for domestication, ready to develop in ways that could not have been dreamt of from an examination of the original wild ‘material’. Delphinium elatum is emphatically adaptable, and with help from a few other species has produced, in a hundred years or so, all the wonderful garden varieties which are the backbone of the flower border in late June and July.
Modern garden delphiniums — with their longer and larger flowers and greater colour — are not so tough and long-lived as their ancestors. To keep them in peak condition they must be renewed fairly frequently and be grown in rather rich, well drained in winter yet well supplied with water in summer. The real giants have such heavy spikes of bloom that they need to be staked individually to prevent them being blown over by the wind.
The best delphiniums used to be clones, that is, each variety was increased by cutting or division from an original seedling sufficiently distinct and good to be selected for this purpose and given a distinguishing name. Then it was discovered that it was possible to produce seed that would give plants of uniformly high quality and even, in some cases, of all one colour. So the age of the Pacific hybrids, of ‘Astolat’, ‘Black Knight’, ‘Galahad’, ‘Guinevere’ and ‘King Arthur’ had arrived and from them seed selections began to take over from clones, not because they were better in themselves but because they were cheaper to rear and easier to keep free of.
Delphinium seed, though fairly large, loses vitality rather rapidly and, where good germination is the only consideration, it should be sown in late summer or early autumn. The snag is that theare still so small when winter comes that they need protection, more from wet and slugs than from cold. So most gardeners delay sowing until March and either store seed in the bottom of a refrigerator or in hermetically sealed packets. The seed is sown in a cool greenhouse or frame, the seedlings are planted outdoors in a nursery bed in June and many of them will produce a small spike of flowers by late summer or early autumn. The next year they will flower at the normal time, about midsummer.
Delphinium clones are usually increased byrooted in a frame or cool greenhouse in spring. Cuttings are prepared from the young growth when this is 8-10cm (3-4in) long. Each shoot is severed close to the crown of the plant so that it is firm and solid, not hollow, at the base. The cut surface is moistened and dipped in hormone rooting powder and the cutting is then inserted 4-5cm (1-½ — 2in) deep in a mixture of equal parts peat and either sand or Perlite. Keep cuttings moist and shaded until they are rooted; then they can be potted individually in a good soil or peat potting mixture and gradually hardened off in readiness for . Clones can also be increased by division in spring but are seldom as vigorous and healthy as plants raised from cuttings.