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Delphinium - Care Guide

Pruning / Deadheading - Video Tip

Growing Delphiniums

Caring for Delphinium

The delphiniums which we offer are mainly classed as ‘Pacific Hybrids’. These are well known and well proven garden plants which can be relied on to produce (in the right conditions) huge flower spikes in early summer. These varieties include:

Lilac and pink flowers
‘Black Knight’
Deep purple flowers
‘Blue Bird’
Clear blue flowers
Lavender blue with a white eye
Pure white flowers
Lilac flowers
‘King Arthur’
Plum-purple with a white eye
‘Summer Skies’
Light sky-blue flowers

More recently we have introduced new improved varieties from the ‘Highlander Series’ which have double flowers:

Lavender blue
‘Cha Cha’
Pale purple
‘Wishful Thinking’
Lavender blue edged blue

All these delphiniums are perennials although some more formal gardeners may prefer to treat them as annuals and start again with new plants each year. There is really no need to take this approach once you understand what these plants need and how to care for them properly.

If you plan to grow delphiniums which will produce flowering spikes of up to 5ft or more you need fertile well drained soil in full sun. It is very sensible to double dig the ground where you intend to locate these greedy plants and incorporate well-rotted dung or leaf mould in each layer. Once your plants are properly established they will thrive for years so it is well worth the initial effort.

Delphinium flower spikes will definitely need supporting to stop them blowing over in strong winds. Metal supports can be left in place to mark the location of the plants right through the year. This can be unsightly so it is probably best to put the supports in place in early May when the plant is growing strongly so that you can ensure that each flowering spike is actually contained within the support structure.

If you have an established clump of delphiniums you should inspect the new shoots when they are 3-6in tall. If there are more than three or five in each crown the surplus should be cut off with a sharp knife. Then you will get a few much taller flowering spikes rather than more smaller ones.

If time permits, give your plants additional water in the main growing season from April, and on into flowering time in late May, especially in dry spells. A liquid fertiliser (or a granular one around the plants and well watered in) applied weekly then will also improve the quality, height and size of the flower spikes.

Slugs and snails can be a major problem for delphinium growers especially as the chubby new growth shoots first emerge and develop. It is up to you as to whether you control these pests with slug bait or use more natural control methods for removing and disposing of them. A good tip is perhaps not to grow your delphiniums near an old wall with cavities and crevices which will naturally harbour snails. An early morning inspecting of your young plants in April will normally allow you to see and remove the worst culprits. Equally you can encourage thrushes to enjoy the crop of slugs and snails in your garden. The worst of this major threat to your plants can be controlled and overcome without undue effort. It is common to grow lupins alongside delphiniums and the slug problem is common to both.

The next tip for growing delphiniums is perfectly obvious when you think about it but is seldom dealt with properly. Once a flower spike has finished flowering you should cut it off with secateurs at the base just above ground level. This will preserve all the energy in the roots that would otherwise have been wasted in trying to set seeds. Instead your plant will develop more shoots and you may even get a few small secondary flowers. What you will have done is greatly improved your chances of better, bigger flowers next season. When grown in pots the removal of the flowering spikes after flowering is even more critical to the survival of your plants.

Delphiniums can be prone to outbreaks of powdery mildew which can occur in dry spells when the plants become stressed. Improving soil conditions and regular watering will help to avoid this.

In the autumn, and just before your plants die down, it pays to remove all the remaining leaf foliage and clean up the crown of the plant. This reduces the threat of aphid attacks in the next season. Small slugs delight in hibernating in ground covered with rotting leaf vegetation. Tidying up your plants for winter when you are also doing this for so many other herbaceous plants is a necessary chore.

Propagation of delphiniums from seed is a waste of time if you grow different coloured forms. Many newer varieties are grown from tissue culture and do not set seeds anyway. Delphiniums are however easily propagated from thick basal cuttings with solid heels and, ideally, 3-4in long. These can be cut from the base of the crown in early spring and set in the mist bench with bottom heat where they will root quickly and can be potted on for planting out next season.

A brief mention should be made of the two more unusual delphinium varieties which we offer; ‘Princess Caroline’ and ‘Red Caroline’. These have exotic flower colours for delphiniums and are the product of years of breeding work with a reddish but small growing mountain species of delphinium from California. We normally offer these as young plants only at and around the time of the Hampton Court Flower Show where, in pots, they are about to flower. These varieties only have flower spikes of around 1.5-2ft in height. They are more tender than other delphiniums but will survive and grow better in a second season IF the flower spike is cut off immediately after flowering. We know they can and do survive the winters in milder areas.

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