Seedlings start flowering same year after sowing, in their fourth month. The growth of delphiniums halts, when seeds ripen, so inflorescences are best removed after the flowering is over. Delphiniums may flower repeatedly in autumn, if the spent blooms have been removed. Bear in mind that this wears the plant down, as it does not have time to set new buds, which may result in less than spectacular flowering next year. Hence it is advisable to cut the autumn flower spikes at the very root, as soon as they appear.
Delphiniums are best planted in late August or early September to allow them sufficient time to establish themselves. Tall hybrid delphiniums are best planted at 50-60 cm intervals in a sunny location, which is shaded from midday sun by trees, fences or walls. Delphiniums prefer growing in the sun, but midday sun can scorch their flowers, and the flowering will be over soon.
A planting hole for a delphinium should be 50 cm deep, filled with a mixture of compost, peat and garden soil, with an addition of fertilisers, rich in potassium and phosphorus. Aim to achieve the same planting level as before. Water well newly planted delphiniums, and water again in 2 or 3 days, if the weather is dry.
Delphiniums need spring feed, when their shoots grow 10-15cm tall – apply complete mineral fertiliser or watered-down slurry of manure (a bucket of manure to 10 buckets of water; a bucket of slurry being sufficient for 5 plants). An additional feeding with potassium fertiliser is appropriate, when plants start producing their flower spikes.
Delphiniums respond well to mulching with peat or compost, which should be spread to a 2-3cm layer around the base. A vigorous plant produces a lot of flower spikes and soon becomes congested. Shoots can be thinned out, when they grow 20-30 cm tall. First, remove al the weak stems from the centre of the clump. If you can bear to be ruthless enough, and leave only 3 to 5 stems per plant, you will soon be rewarded with exceptionally large flowers on tall flower spikes. Besides, the removed shoots can be rooted to produce new plants.
The plant supports should be installed, when plants grow 40-50 cm tall. A plant needs 3 to 5 twigs, around 1.8m long. All stems need to be tied in, since they break easily in the wind. The stems can also be tied around with a wire, which is attached to a stake. The support will soon be mask by foliage, and stems will grow well-supported.
The weakest spot of the delphinium is where stems attach themselves to the crown: they break easily, so are best tied in two places, 40-50 cm and 100-120cm above the ground. If the flower spikes are especially tall and heavy, they should be tide in at three levels – at 40, 80 and 120 cm above the ground.
In a prolonged dry spell plants should be watered every week, 2-3 buckets of water per plant. A shallow frequent watering brings more harm than use. The caked-up soil should be tilled regularly. Delphiniums need most water, when they are setting flowers. At times flowers get aborted on the spike due to the heat, or they flower inconsistently along the spike. Sometimes plants produce deformed inflorescences, if they are short of potassium or phosphorus.
