How To Grow Delphiniums

Add height to your border with majastic spires of of blooms

Delphiniums at Holehird the Lakeland Horticultural Society garden at Windermere, Lake District (pictured above)

Delphiniums are hardy perennials and an absolute must for the herbaceous border, adding height with their magnificent spires of blooms. Their main colour is the iconic blue but they also come in pinks, cream, white and apricot. They range in size from 90cm (3’) to over 180cm (6’). They are part of the larkspur family and as such all parts are toxic to both humans and animals, so if you have sensitive skin wear gloves when handling them. They originate from the northern hemisphere and the mountains of tropical Africa. Despite their toxicity they are an important source of nectar for butterflies and bees.

They make a wonderful cut flower, just cut as soon as the blooms start to open and the plant will produce another spike. Add a couple of drops of bleach to the water and change every week.

Coral Sunset

Position

They need a sunny, sheltered site out of strong winds as they soon become battered by heavy rain and strong winds despite being staked. They can tolerate a little shade but too much shade will affect their ability to flower to their full potential, flowers will be smaller and stems weaker. The soil needs to be an alkaline, well-draining, fertile loam as they are really greedy plants.

Planting

Dig a hole about twice as big as the root-ball and enrich with some well-rotted farmyard manure, home-made compost or good quality peat-free compost. Add some balanced fertiliser such as Growmore or blood, fish and bone. If your soil is neutral add some lime or wood ash to increase the alkalinity. Plant with the top of the root ball level with the soil surface.

Aftercare

Keep well-watered as they cannot tolerate being dry, their favourite growing season is cool and damp, so an ideal plant for us here in the Lake District. They do not perform well when the weather is hot and dry. Stake when the plant is about 20cm (8”) tall; you can get away with a circular support which goes around the whole plant if growing dwarf varieties but the tall ones will need a cane for each bloom. Add a top dressing of lime or wood ash in spring. Restrict the number of spikes grown to 2 - 3 on a young plant and 5 – 7 on an older established clump, otherwise if you let a lot of spikes form on each plant the resulting blooms will be smaller and weaker. Feed with a balanced fertiliser every couple of weeks during the growing season.

Dead head by cutting the spent spike back to the next side shoot. Once the spike has finished flowering cut off at the base and the plant may produce another smaller flower later on in the summer. Although they are hardy, if there is a severe winter forecast protect the crown with a good thick layer of mulch or an upturned hanging basket stuffed with straw or sheep’s wool.

Propagation

Divide a large established clump in the spring. Pot up the new growth from around the outside and discard the central portion. Pot up into a good quality multi-purpose compost.

Pests and diseases

Slugs and snails are a huge problem as they look on delphiniums as a 5* Michelin restaurant. Take every measure possible to protect your plants especially when the new shoots come through in spring.

Powdery mildew can also be problematic in a dry, hot summer so make sure they don’t dry out and are always well watered and that they have a good airflow around them. At the first sign spray with a fungicide to try and prevent it spreading.

Moonlight

Recommended varieties

• Blue Tit  -  indigo blue with a black eye; 105cm (3.5’)
• Butterball  -  cream; 150cm (5’)
• Cupid  -  pale blue with a white eye; 90cm (3’)
• Moonbeam  -  pure white; 165cm (5.5’)
• Pink Ruffles  -  palest pink; 150cm (5’)