How to grow delphiniums

In this short video guide, the experts at Home Farm Plants share their top tips for growing delphiniums, including how to keep them safe from slugs and caring for them over winter.

Jump to:

• Planting delphiniums
• Caring for delphiniums
• Delphinium pests and problems
• Where to buy delphiniums
• Delphiniums to grow

Where to grow delphiniums

The best place to plant delphiniums is in moist but well-drained soil in full sun. Delphiniums are tall plants, so do best at the back of a sunny border. Avoid windy spots, as wind can blow the plants over, and make sure they have plenty of space to develop without being shaded out by other plants.

How to plant delphiniums

You can plant a delphinium at any of time of year, but spring or autumn is best as the soil will be warm and moist. Dig a planting hole and add compost or well-rotted manure in the bottom, for a nutritious boost. Delphiniums struggle in winter wet, so add grit to heavy soils to aid drainage. Plant your delphinium at the same depth it was growing in the pot, and back-fill with soil, firming in gently. Water in well.

How to care for delphiniums

Delphiniums need care to keep them looking good. They need protecting from slugs in spring, moist soil and plenty of feeding. Spring is the best time to stake taller varieties, either with canes or using a frame that plants can grow up through. Delphiniums thrive in cooler temperatures, with slightly moist soil in summer, so make sure plants don’t dry out in hot weather. They are hungry plants, which means that they need feeding regularly. Apply a liquid fertiliser every couple of weeks once the first shoots appear to encourage strong growth.

Although Delphiniums have a relatively short flowering season, cutting the flower spikes back as soon as they have faded can encourage plants to produce a few flowers in late August or September.

To cut back a delphinium:

1. As soon as the flower spikes starts to look tatty, cut every flowered stem right down to the ground, leaving any developing side shoots, and the remaining foliage at the base
2. Water the plant well

Here, Monty Don demonstrates how to cut back delphiniums after they've flowered in early summer:

In autumn, once the plant has finished flowering, cut the plant back down to the ground.

To keep plants flowering well, you can divide them every few years, in spring.

How to take delphinium cuttings

To take basal cuttings from a delphinium:

1. In spring, when the new shoots appear, take a sharp knife and cut a shoot, just below the surface of the soil. Take one or two shoots from each plant
2. Place the cutting immediately into a polythene bag, to keep moisture in
3. Cut off some foliage from the top of the cutting, leaving a few leaves to feed the roots
4. Pot up each cutting into a small pot filled with multipurpose compost and perlite
5. Water and cover with a polythene bag to keep moisture in, or mist regularly, to stop the leaves drying out
6. Keep in the greenhouse or on a sunny windowsill

How to propagate delphiniums

The best method of propagating delphiniums is to take cuttings from the base of the plant (basal cuttings) in spring. You can also save delphinium seed to sow from February to June, or September to October. Sow in small pots or seed trays and keep at a temperature of around 10°-15°C.

Here, Monty explains how to pot on rooted delphinium cuttings:

Pests and diseases

In spring, as soon as the new shoots appear, protect them from slugs and snails or they will demolish the fresh new delphinium leaves. Use a garlic drench, organic slug pellets, or a biological control (which is only effective against slugs).

Delphiniums can be susceptible to powdery mildew in dry weather, so keep the soil around them moist. They can also be affected by rust, which causes rust-coloured pustules on the foliage. Pick off any affected leaves as you see them and clear up any fallen leaves in autumn.

Delphinium black blotch is a bacterial infection that causes large black blotches on leaves. It is particularly common in wet summers and can affect the health of the whole plant. The only treatment is to remove affected plants to prevent the spread of this disease.

Delphinium varieties to grow

Most delphiniums are hardy perennials, but annual and biennial varieties are also available. The Elatum Group of delphiniums are the most commonly grown and are the tallest type, with spikes of single or double flowers reaching up to 2m. Belladonna delphiniums are shorter, with a looser, more branching habit and single flowers. 'Pacific Hybrids' were developed in the 1950s and 1960s, and are short-lived perennials or biennials. They look similar to 'Elatum' delphiniums but are shorter. The 'Magic Fountain' series of delphiniums are short and more compact, suitable for smaller gardens.

Delphinium ‘Amadeus’ – a gorgeous blue delphinium, bearing velvety, deep-purple/blue flowers with a dark brown ‘eye’. It makes a spectacular cut flower.

Height x Spread: 1.5m x 1m

• Buy Delphinium 'Amadeus' from Blackmore & Langdon

Delphinium 'Pacific Hybrids' – tall, stately plants in a range of colours. They are short-lived perennials.

H x S: 150cm x 75cm

• Buy Delphinium 'Pacific Hybrids' from Thompson & Morgan
• Buy Delphinium 'Pacific Hybrids' from Van Meuwen

Delphinium 'Rising Stars' – a mix with single or double flowers in a variety of colours. Grown together they make a dramatic display, and they also make fantastic cut flowers.

H x S: 150cm x 75cm

• Buy Delphinium 'Rising Stars Mixed' from Thompson & Morgan
• Buy Delphinium 'Rising Stars Mixed' from Van Meuwen

Delphinium 'Magic Fountain Series' – compact plants, suitable for smaller gardens. They come in a range of colours, often with a contrasting eye at the centre.

H x S: 90cm x 60cm

• Buy Delphinium 'Magic Fountain Mixed' from Primrose
• Buy Delphinium 'Magic Fountain Mixed' from Thompson & Morgan

Delphinium elatum 'Faust' – bears incredibly tall spikes of intense blue double flowers, with a dark centre.

H x S: 2.5m x 1m

• Buy Delphinium elatum 'Faust' from Primrose
• Buy Delphinium elatum 'Faust' from Blackmore & Langdon

Delphinium elatum 'Cinderella' – a compact, pale pink delphinium with very sturdy stems and triple blooms that was voted BBC Gardeners' World Live 'Best New Plant Introduction for 2019'.

H x S: 1.2m x 80cm

• Buy Delphinium elatum 'Cinderella' from Suttons

Delphinium ‘Vespers’ – this variety is a pale mauve and blue delphinium with semi-double flowers that have white eyes

H x S: 1.5m x 1m

• Buy Delphinium ‘Vespers’ from Blackmore & Langdon’s

Delphinium ‘Pandora’ – semi-double light blue flowers with eye-catching black and blue striped centres

H x S: 1.5m x 1m

• Buy Delphinium ‘Pandora’ from Blackmore & Langdon’s

Frequently asked questions

Is Delphinium poisonous to humans?

Delphiniums are poisonous to humans, pets and livestock. Wear gloves and other protective equipment when handling them.

Do delphiniums come back each year?

Many delphiniums are hardy perennials so they should come back each year. If they don't come back after the first year, check that the soil is not waterlogged as this can cause them to rot in winter.