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Home & garden.

Updated: 9 May 2022

How to grow delphiniums and best varieties

Delphiniums tower over other plants in the border and return every year. Discover our best delphinium varieties and tips for how to grow them.
Ceri Thomas
Delphiniums

The towering spires of blue created by delphiniums are a quintessential cottage-garden favourite. Modern breeding means that blue isn’t the only option, and delphiniums are available in a surprising range of colours and flower shapes. 

Unfortunately, delphinums have a reputation for not being the easiest plants to grow. Elatum varieties are tough and hardy, but Pacific hybrids are more tender and can easily disappear over winter. Slugs and snails delight in feasting on the tender shoots, and the stems are brittle and tend to snap when the notoriously fickle British summer weather turns bad. And, no matter whether your border is damp or not, delphiniums most often get infected with the dreaded powdery mildew

Which? Gardening magazine grew a range of popular varieties over two years to see which would give us the best display.


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Key facts

PLANT TYPE Hardy perennial

POSITION Full sun or light shade

SOIL Moist, fertile and neutral

How to grow delphiniums: month by month

JanuaryFebruaryMarchAprilMayJune

CUT BACKPLANT/FLOWERINGPLANT/STAKESTAKEFLOWERING
JulyAugustSeptemberOctoberNovemberDecember
FLOWERINGFLOWERINGPLANTPLANT

Best delphinium varieties

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Full testing results for delphiniums

Variety nameOverall ratingHeight x spread (cm)Flowering durationImpact of flowersImpact of displaySupport neededFlower head shapePollinator attractionPests & diseases
180 x 40

140 x 40

200 x 60

120 x 40

180 x 30

110 x 30

180 x 60


How we test delphiniums

In spring, the Which? Gardening magazine researchers ordered three plants each of 24 varieties of delphiniums. We included short and tall varieties, as well as elatum and Pacific hybrids, in a range of colours. We choose double flowers, as well as belladonna types that are more like the softer wild larkspur. The plants were planted in the Which? Gardening magazine trial beds at Capel Manor, north London, in May. We recorded how the delphiniums grew throughout two summers, assessing flowering and any pests and diseases. We didn’t stake plants unless they needed it and did so before they flopped completely. We watched out for any pest or disease problems.

Caring for your plants

Planting

Delphiniums aren’t fussy about soil type, providing it’s moisture-retentive in summer but free-draining in winter. Add plenty of grit to heavy soils to help with drainage. Plant your delphiniums at least 60cm apart to allow air to circulate and reduce the chances of powdery mildew. They look at their best in groups of three or more.

Thinning

Established delphiniums will produce several new stems in spring. To encourage the largest blooms, retain only up to seven of the healthiest stems. This thinning will also allow air to circulate and help to prevent powdery mildew.

Staking

We tried several methods of staking and found that the best method is to support lower down with a more flexible support. Making a loose cage of string worked fairly well for us, as did metal spiral supports. If you want to make cages, insert several canes around the plant when the shoots are around 30cm tall. The canes should be linked with soft string. This will allow the stems to move in the wind, while providing adequate support. Ideally, both canes and string will be obscured by the developing foliage, although we found that sometimes the support was visible.

Feeding

Delphiniums are hungry feeders, and require a mulch of well-rotted garden compost in spring. They also appreciate a scattering of blood, fish and bone, Vitax Q4 or growmore a couple of times through the summer.

Common growing problems

Slugs and snails

Slugs and snails are the pests most damaging to delphiniums, completely devouring their soft leaves and emerging stems. They are a problem throughout the growing season, but especially in spring.

Read more about slugs and snails

Powdery mildew

Powdery mildew can also be a concern, especially if your soil becomes dry during summer. Remove any leaves showing the distinctive white coating and keep your plants well-watered, avoiding wetting the foliage. Applying mulch in spring will help to avoid the problem by conserving moisture, as will spacing plants so there is good air circulation.

In autumn/winter, as foliage dies down, remove any dead leaves to prevent rot spreading to the crown of the plant.

Read more about powdery mildew