Delphiniums are tall, spectacular plants known as the ‘Queen of the Border’. They are one of the few garden plants that flower true blue but also may be mauve, purple, pink, cream, white or bicolour.
Surprising to most gardeners, is the fact that there are over 350 delphinium species, primarily native to mountainous regions. This explains the need for sunny and well-drained conditions. Often delphiniums are thought of as difficult and time consuming to grow but this is not the case. The British strain is very hardy, disease resistant and relatively trouble-free. While like all plants, they thrive in ideal conditions, a few basic growing techniques will ensure quality spikes. Delphiniums will grow well in most soil types but the soil should never become waterlogged as this will promote crown rot. It may be necessary to raise the soil-level slightly for improved drainage. Prepare the site well by removing all perennial weeds and adding slow release fertilizer such as compost, bone meal or well-rotted manure.
When planting, water the hole well, position the plant at the same depth as in the pot, firm the soil and water again, checking the soil level. Larger size, strong, quality potted plants will adapt better especially in established gardens. Water the plant as required depending on weather conditions. After the first year, delphiniums produce a coarse anchor root in addition to their fibrous roots so they resent being moved.
In early spring, it is recommended to remove the weaker stems just above ground-level so the larger stems increase in size and strength. This simple task will greatly improve the floral display produced. Spring is also the easiest time to insert three strong four-foot bamboo stakes around the delphinium. As the plant grows, garden twine can be tied from stake to stake at the base of the flower spike. This cord will provide support for the stems during times of strong winds but allow them to move, shaking off the rain.
An established delphinium is quite drought tolerant since the main growth periods are in the cool, moist spring and autumn. A thorough watering once a week preferably at soil level will reduce stress on the plant. Mulching may be beneficial but not directly over the crown of the plant. Frequent watering by overhead sprinklers may encourage mildew.
After the delphinium has flowered, deadhead it but leave as much foliage as possible to promote strong roots. Most gardeners design their beds with other plants in front of their delphiniums to hide the dying foliage. Delphiniums usually repeat bloom in the autumn with new growth appearing in the cooler moist weather. If you allow the plant to set seed it is less likely to repeat bloom.
In late autumn, cut the plant off at ground level and clear the beds of all debris to reduce the possibility of spring slug damage. Do not mulch over the crown as this also promotes rot. The British and Canadian strains of delphiniums have been bred for winter hardiness and will enjoy a good snow cover if Mother Nature provides it. However more important to their survival is the winter rest period, also enjoyed by Canadian gardeners.
Blossom Hill Nursery