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