Delphinium requienii

This delphinium is a biennial and originates from the Isles d'Hyeres (S. France), Corsica and possibly Sardinia. It would be rather surprising if a species from these locations was completely hardy. In our experience over the last twenty years, small seedlings do survive most winters in Britain and then provide an interesting flower display the following summer. The plants are prolific seed producers and hundreds of self-sown seedlings, as seen in the picture, ensured that this delphinium could be found somewhere in our garden almost every year.

Seedlings of D. requienii can be transplanted without difficulty, so it is easy to lift and pot them up so that some can be given greenhouse or cold frame protection during the winter.

The seeds are large compared to those typical of cultivated garden delphiniums. Sown in moist multi-purpose compost, germination occurs in 14 to 21 days when the seed tray is kept at 15 - 20°C. It is important to keep seed trays in good light once germination starts, otherwise the stems of seedlings extend extremely quickly. This year during March, for example, seedlings kept on a window ledge grew 50 - 75 mm tall in about 3 days! It would have been better to transfer the pots to the greenhouse to obtain sturdy seedlings despite the low temperatures. Seedlings are pricked out once the first true leaf is well developed. At this stage, the fleshy stems and characteristic glossy leaves are already apparent and the plants soon grow quite large, even at low temperatures.

If seedlings in the open ground grow too large before the onset of winter, they become prone to attack by botrytis, especially after snowfalls. It is possible that the initial tissue damage is caused by freezing. During the past winter, two large plants with stems 50cm tall and 25mm thick that had almost reached flowering by late October were killed by frost during January. The large leaves looked undamaged but the fleshy stems collapsed and rotted.

Seedlings that survive through the winter develop to very large plants up to 2 m tall with many branches and side spikes when growing in fertile soil. In a dry inhospitable site they remain dwarfed at perhaps 30cm tall but will still flower and set seed. When handled, the large fleshy leaves have an unpleasant odour which reminds us that delphiniums are poisonous.

Each plant develops a long terminal raceme or flower spike with many fairly small florets. Vigorous plants also develop several large secondary flowers spikes from leaf axils on the main stem. Further smaller flowering branches develop in succesion from almost every leaf joint on the plant so that a plant may have hundreds, perhaps thousands, of individual florets. The flowers are very attractive to bees, and a group of plants in flower can have hundreds of bees buzzing around.

The florets are about 25mm across with a spur about half the length of the sepals, which are pale pinkish-violet in colour with purple veining on the back surface. The prominent group of dark purple stamens add to the curious charm of these flowers. As the pictures show, the flowers and stems are clothed in fine hairs.

After pollination, each floret develops three carpels containing ten or more seeds. Flowering extends over many weeks due to the development of flowers on lateral and sub-lateral branches but the plant dies when flowering is over.

Clonal variation During the past year, plants of D. requienii from two sources were grown from sowings in February. Plants raised from our own seed made a lot of growth but without signs of flowering. Another batch raised from seed from the Hardy Plant Society (labelled as D. staphisagria) differed in several respects. At all stages, the form of the plants in the two groups was identical, as were the flowers, but the foliage of the HPS batch was a much darker green and there was heavier purplish staining of the stems. The plants of the HPS batch also all developed flower stems and many flowering sideshoots, although the flowers were destroyed by wet conditions and grey mould (botrytis) during October. Several plants in both batches were lost due to the development of black rotting regions in the thick fleshy stems at the soil surface during the summer.