How to grow delphiniums - Delphinium 'Cassius'

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

Delphiniums produce wonderful tall, vertical spires laden with intensely-coloured flowers in the peak of summer.

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Also known as larkspur, delphiniums are traditionally a cottage garden staple, bringing height and colour to borders. The flowers are also loved by bees and are great for cutting. There are many delphinium cultivars available, ranging in colour from blue through to mauve, pink and white.

Delphiniums look good in a cool-coloured planting scheme, and also work with other vertical summer flowers, such as lupins and verbascums.

How to grow delphiniums

Grow delphiniums in moist but well-drained soil in full sun – delphiniums struggle with winter wet so aid drainage by adding grit to the planting hole if you have heavy soil. Stake emerging flower stems in spring and start feeding 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:


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.


How to plant delphiniums

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

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 propagate delphiniums

Sowing Delphinium 'Galahad'
Sowing delphinium ‘Galahad’ in small pots

The best method of propagating delphiniums is to take cuttings from the base of the plant in spring. Here, Monty Don explains how:

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

You can also grow delphiniums from seed – many varieties are available to buy from seed, or you can try saving your own.


How to care for delphiniums

Tying in delphinium stem to a support
Tying in delphinium stem to a support

Delphiniums are hungry plants. Apply a liquid fertiliser every couple of weeks once the first shoots appear to encourage strong growth. This 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 later flowers.

Here, Monty Don demonstrates how to cut back delphiniums after they’ve flowered:

Although hardy, being herbaceous perennials, delphiniums will die back over winter.


Growing delphiniums: problem solving

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

In spring, protect plants from slugs and snails – they will demolish the fresh green new growth of young delphiniums. Delphiniums can be susceptible to powdery mildew and rusts and delphinium black blotch, which can be spotted on leaves, but affects the whole plant. The only treatment is to remove affected plants to prevent the spread of this disease.


Delphinium varieties to grow

Delphinium 'Amadeus'
Delphinium ‘Amadeus’
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  • 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. They’re ideal for growing towards the back of a sunny border
  • Delphinium ‘Fanfare’ – bears semi-double, lilac, mauve and blue flowers, with a white centre or ‘eye’. It’s ideal for growing towards the back of a sunny border, and works well with flowers in other shades of blue
  • Delphinium nudicaule ‘Redcap’ – an unusual compact variety, with orange-red flowers and purple tinged foliage that greens up as it matures. Delphinium nudicaule is a short-lived hardy species, native to California. For best results, grow ‘Redcap’ in full sun or dappled shade, in moist, well-drained soil
  • Delphinium ‘Bruce’ – bears velvety flowers in a deep purple, with buff eyes. It’s ideal for growing towards the back of a sunny border, and works well with flowers in other shades of blue
  • Delphinium ‘Turkish Delight’ – has pretty, semi-double flowers in the palest pink-mauve, with a lighter ‘eye’