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How to grow delphiniums – Delphinium 'Faust'

How to grow delphiniums

All you need to know about growing delphiniums, in this detailed Grow Guide.

A table displaying which months are best to sow, plant and harvest.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sow
Sow

Do not Sow in January

Do not Sow in February

Do Sow in March

Do Sow in April

Do not Sow in May

Do not Sow in June

Do not Sow in July

Do not Sow in August

Do not Sow in September

Do not Sow in October

Do not Sow in November

Do not Sow in December

Plant
Plant

Do not Plant in January

Do not Plant in February

Do not Plant in March

Do not Plant in April

Do Plant in May

Do Plant in June

Do not Plant in July

Do not Plant in August

Do not Plant in September

Do not Plant in October

Do not Plant in November

Do not Plant in December

Flowers
Flowers

Plant does not flower in January

Plant does not flower in February

Plant does not flower in March

Plant does not flower in April

Plant does not flower in May

Plant does flower in June

Plant does flower in July

Plant does flower in August

Plant does flower in September

Plant does not flower in October

Plant does not flower in November

Plant does not flower in December

Cut back
Cut back

Do not Cut back in January

Do not Cut back in February

Do not Cut back in March

Do not Cut back in April

Do not Cut back in May

Do not Cut back in June

Do Cut back in July

Do Cut back in August

Do Cut back in September

Do Cut back in October

Do not Cut back in November

Do not Cut back in December

  • Plant size

    2m height

    90cm spread

Nothing quite beats the drama of delphiniums. In June and July, they produce towering flower spikes that can reach over 2m tall. They are probably best known for their vivid sapphire blue shades, but they also come in mauve, pink, white and even red. The flowers can be single or double, depending on the variety.

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Delphiniums are a cottage garden and herbaceous border staple, bringing height and colour and mixing well with roses, peonies and other vertical flowers such as lupins and verbascums. The flowers are loved by bees and look stunning in a vase.

Delphiniums are in the buttercup family (Ranunculaceae) and have been grown in the UK for centuries. The word delphinium comes from the Greek delphinos, meaning dolphin, probably because of the shape of the opening flowers. Their common name, larkspur, dates back to Tudor times. 

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.

Delphiniums need care to keep them looking good. They need protecting from slugs in spring, staking, moist soil and plenty of feeding. If you cut them down to the ground after flowering, you may be rewarded with a second flush of flowers in September. 

How to grow delphiniums

Grow delphiniums in moist but well-drained soil in full sun. Delphiniums struggle in wet winter soil, so aid drainage by adding grit to the planting hole if you have heavy soil. Protect emerging shoots from slugs in spring and stake as soon as they start to grow. Feed weekly with a high potash fertiliser. After flowering, cut stems back to encourage a second flush of blooms. Mulch in autumn with well-rotted manure or leaf mould.

More on growing delphiniums:

Delphiniums: jump links


Where to grow delphiniums

How to grow delphiniums - where to grow delphiniums
How to grow delphiniums – where to grow delphiniums

For best results grow delphiniums 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.


How to plant delphiniums

How to grow delphiniums - planting delphiniums
How to grow delphiniums – planting 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

How to grow delphiniums – tying in delphinium stem to a support
How to grow delphiniums – tying in delphinium stem to a support

Delphiniums 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.

Spring is also 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.

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 propagate delphiniums

Sowing Delphinium 'Galahad'
How to grow delphiniums from seed – sowing Delphinium ‘Galahad’

You can grow delphiniums from seed. Many varieties are available, or you can try saving your own. Sow from February to June, or in September or October. Sow in small pots or seed trays and keep at a temperature of around 50°-60°F.

The best method of propagating delphiniums is to take cuttings from the base of the plant (basal cuttings) in spring.

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

Here, Monty Don explains how to take basal cuttings from delphiniums:

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


Growing delphiniums: problem solving

How to grow delphiniums - problem solving
How to grow delphiniums – problem solving

In spring, as soon as the new shoots appear, protect them from slugs and snails – they will demolish the fresh green new growth of young delphiniums. 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.


Advice on buying delphiniums

    • Bear in mind that delphiniums can become large, tall plants so check the ultimate size of the variety you are interested in
    • Delphiniums grow best in a sunny spot so check that you have the right conditions in your garden
    • You can buy delphiniums at nurseries and garden centres, or from specialist retailers online. An economical way to buy delphiniums is to look out for small plug plants in spring
    • Look for healthy, green foliage with no signs of pests or disease

Where to buy delphiniums online

Delphinium varieties to grow

Delphinium 'Amadeus'
Delphinium ‘Amadeus’

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

Height x Spread: 1.5m x 1m

Delphinium ‘Pacific Hybrids’ – tall, stately plants in a range of colours. They are shortlived perennials.

H x S: 150cm x 75cm

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

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

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

H x S: 2.5m x 1m

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

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