July brings the delphiniumon towering spikes 5 to 7 ft. high, and the modern, shorter 4 ft. varieties which need little or no support. These hardy plants die to the ground in autumn and produce new shoots the following spring. They are used most frequently in herbaceous borders, mixed borders and in front of shrubs. Few flowers are so pure a blue; there are also many varieties with mauve, purple, violet, or white flowers. Early in the 19605 the first hybrid reds, pinks and yellows were bred by Dr R. A. H. Legro in Holland.
Generally described as hybrids of D. elatum, modern delphiniums are a mixture of more than half-a-dozen species. D. belladonna and its varieties are not so widely grown today. They produce several spikes on each main. D. belladonna tolerates light shade, but other delphiniums demand open, sunny positions, sheltered if possible from wind. Soil Although a good garden loam is ideal, sandy or clay soils can be improved by digging in plenty of rotted manure, peat, leafmould, rotted or spent mushroom compost. Dig 18-20 in. deep, mix in 4 oz. per square yard of a general fertilizer and let the ground settle for at least a month before planting.
July to October, or March, are the best times to plant, except in heavy, wet ground or where slugs abound, when spring is preferable. A space 2 ½ ft. across each way is sufficient in a border, but plants intended to produce spikes of exhibition quality deserve spaces 3 – 3 ½ ft. across. Young plants knocked fromcan be set with a trowel; those from open ground often arrive with their ‘balled’ in soil and then the roots must be spread out, keeping the crowns of the plants at surface level. Firm planting is essential.
Delphiniums are increased by, division and . does not come true; that from a blue-flowered plant may produce with mauve, purple and white flowers. However, the best quality produces excellent plants cheaply. Preferably freshly harvested seed in August or early September, in seed boxes filled with J.I. compost. Stand the boxes in a frame, or sheltered spot outdoors. By late April or May seedlings are big enough to plant 1 ft. apart in a nursery bed outdoors and are moved later to their permanent positions.
Named varieties will come true only when propagated by dividing clumps in early spring, when the shoots are 3-4 in. high, or by cuttings. The roots are teased apart and the crown served with a knife so each new portion has roots and one or two shoots. Cuttings generally produce sturdier plants. They are made by choosing healthy shoots 3-4 in. high, scraping soil from around them beforethem off close to the crown. Strip off their lower , dip the lower ends of the in water, then in and set them with a dibber, about five in a 44-in, pot of compost.
Bury one third of each stem, water the cuttings, and place them in a propagating case, or on a shadedbench. They in six to eight weeks and then are potted up singly in 3 ½-in, pots of
In early spring crowns should be covered with ashes or coarse grit to keep slugs off the young shoots. Thin these out to leave the strongest four to six per plant, when 6 in. tall. Knock in a 6-8 ft. cane beside each shoot; tie the stems to the canes as they grow. Feed each plant with a heaped trowelful of dried blood in May, the same amount of general fertilizer in early June, and a tablespoon of sulphate of potash as the flower buds show colour,in these plant foods. Keep the soil damp. Dead flower spikes should be cut back; secondary spikes sometimes develop and bloom in early autumn.