How to grow Delphiniums

Posted in All Gardening Advice, Annuals, March, April, May, on

We have all got to grow delphiniums – the most statuesque towering spires for any garden. They make brilliant cut flowers too.

Flowers: June-July and August-September. Height: 1.5-1.7m

Growing from seed

Sow under cover in a seed tray March-April, then grow on and plant out in summer.

Or sow under cover in August, overwintering in a cold frame, to plant out the following spring.

Planting out seedlings

Choose a site in full sun or dappled shade, with well-drained soil. Add plenty of grit to heavy soils to help with drainage. If delphiniums sit wet in their dormant winter season, they can die, so make sure you prevent this.

Add plenty of organic matter to the planting hole; choose something slow-release, like Blood, Fish and Bone, or a scattering of bone meal.

They look at their best in groups of three or more, but plant seedlings 60-75cm apart to help prevent mildew.

Delphiniums will need sturdy staking to keep their hollow stems upright. You could use bamboo canes to create a 'cage', or if you prefer your supports to be nearly invisible, use canes to create a horizontal grid placed at 4-5ft for your delphiniums to grow through.


Slugs love delphinium shoots, so a dose of Nemaslug will help protect your plants.

Thin out shoots emerging from crowns early in the season to increase air circulation and help prevent powdery mildew forming.

Delphiniums are hungry feeders, so feed again with Blood, Fish and Bone a couple of times through the summer, then again in autumn before the plants die down.

Delphiniums will flower June-July. Cut to the ground after their first flowering to get a second flush August-September.

Read more from Sarah about different methods of slug and mildew prevention in her Caring for Delphiniums article.

Cut Flowers

Delphiniums make great cut flowers in June, when most flowers are open, and will last up to 7 days in a vase.

For tall spires, insert a cane into the hollow stem to avoid it bending and breaking.

Keep your arrangement away from fruit bowls as they are sensitive to ethylene gas which is omitted when fruit ripens.

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