How to grow delphiniums
All you need to know about growing delphiniums, in this detailed Grow Guide.
|Plant Size:||Height: 2m||Spread: 90cm|
Nothing quite beats the drama of delphinium flowers. In June and July, they produce towering flower spikes that can reach over 2m tall. They're probably best known for their vivid sapphire blue flowers, but they also come in mauve, pink, white and even red. Delphinum flowers can be single or double, depending on the variety.
Delphiniums are a cottage garden and herbaceous border staple, bringing height and colour to displays 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.
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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
- Planting delphiniums
- Caring for delphiniums
- Delphinium pests and problems
- Where to buy delphiniums
- Delphiniums to grow
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
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 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 they have a relatively short flowering season, cutting delphinium 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:
- 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
- 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
You can grow delphiniums from seed. Many varieties are available, or you can try saving your own. Sow delphinium seeds 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:
- 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
- Place the cutting immediately into a polythene bag, to keep moisture in
- Cut off some foliage from the top of the cutting, leaving a few leaves to feed the roots
- Pot up each cutting into a small pot filled with multipurpose compost and perlite
- Water and cover with a polythene bag to keep moisture in, or mist regularly, to stop the leaves drying out
- 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
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’ – 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
Delphinium 'Pacific Hybrids' – tall, stately plants in a range of colours. They are shortlived 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
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