With wonderful spikes of vibrant colour, I love adding Delphiniums to my garden borders. Did you know that the Delphinium is the birth flower for people born in July? Being such a wonderful plant to grow, find out the answers to Google’s most asked questions.

Where are Delphiniums native to?

Delphiniums are native to the Northern Hemisphere from the United States, Europe, Asia and Northern and Central Africa.

They thrive in cold and moist climates.

Delphinium wildflowers in San Francisco

Are Delphiniums annuals, biennials, or perennials?

Most Delphiniums are hardy perennials, but annual and biennial varieties are also available.

You might also see them called ‘larkspurs’, which are the plants’ common name originating in the Tudor era. Sometimes the term Delphinium is used to refer to perennial varieties, and Larkspur refers to annual plants.

Did you know that the name Delphinium comes from the Greek ‘delphinos’, which means dolphin. It is thought this name is about the shape of the flowers once they open up.

Which garden style are they best suited for?

Delphiniums are a cottage garden and herbaceous border staple, bringing height and colour to displays.

I find that Delphiniums mix well with roses, peonies, and vertical flowers like lupins and verbascums.

Delphiniums in a cottage garden

How do you grow Delphiniums from seed?

Sow Delphinium seeds undercover in March and April.

For best results, sow them undercover in August or September and overwinter them in a cold frame, before planting them out in spring.

sowing seeds in small pots

Sow them into small pots or seed trays and keep at a temperature of around 10 to 15 degrees Celsius or 50-60 degrees Fahrenheit.

Your new seedlings should appear in 14 days.

And your new plants should flower in around 18 months.

You may get a small bloom the first year after sowing, but you will get stronger flower production in the second year.

How long do Delphiniums take to germinate?

Delphinium seeds germinate best at low temperatures (15 to 20 degrees Celsius), and keep the seed moist throughout the germination period.

It typically takes 14 to 21 days for the seed to germinate, but it can range from 5 days to 5 weeks depending on the variety.

Are Delphiniums easy to grow?

Delphiniums are a challenge for new gardeners as they need extra TLC.

They are hungry plants so need a liquid fertiliser every couple of weeks once the first shoots appear. This will also encourage new growth.

Spring is the best time to stake taller varieties, I use canes, but you can use frames that the delphinium can grow up.

They need protection from slugs in spring, so make sure you make it difficult for these bugs.

Where do they grow best?

For best results, grow Delphiniums in moist, well-drained soil, in full sun or dappled shade. 6 to 8 hours of sun a day is a great target to aim for.

They are tall plants, so do best at the back of sunny borders. Avoid windy spots, because the wind can blow the plants over.

Delphiniums growing in dappled shade

How do you grow Delphiniums?

Plant Delphiniums at any time of year, although spring or autumn is best when the soil is warm and moist.

Dig a planting hole and add some peat-free compost, or well-rotted manure to the bottom. Delphiniums need nutrient-rich soil, so when planting out add organic matter to the hole.

Add some grit to heavy soils if it’s a wet winter. This will help with drainage.

Plant your Delphinium at the same depth it was growing in the pot, and back-fill with soil, firming it in gently.

Finally, water your new plants in well.

How long do they live for?

Delphiniums typically have a life span of 2 to 3 years.

How big do they grow?

Delphiniums fall into three groups based on their appearance and size.

The belladonna group have loosely branched flowers with lots of side spikes, they flower in early and late summer. The upright branching plants can reach 1 to 1.2 metres high, and 45 centimetres wide.

The elatum group beat the tallest flower spikes, which can be up to 2 metres high. They flower in early to midsummer and often again in autumn when cut back. The clump-forming plant grows 1.5 to 2 metres high and 90 centimetres wide.

Pacific hybrids reach 1.8 metres tall and 75 centimetres wide.

Small delphinium from belladonna group - 'Atlantis'
Medium delphiniums from elatum group
Large pacific hybrid delphiniums - 'Galahad'

How long do Delphiniums flower for?

Delphiniums have a relatively short flowering season, with a first flush between June and July, and a second flush between August and September if cut back properly.

When should I feed/fertilise them?

They are hungry plants, so feed them weekly during their flowering season with high potash or tomato feed to keep them healthy.

Make sure to keep up this routine from when the flowers begin to emerge, through both flushes of flowers until August.

Will Delphiniums flower twice?

Delphiniums typically bloom in June and July. They can, however, flower twice in one year.

Cut your flowers back as soon as they are past their best and look a little ragged. Cut the flowering spike right back to the ground leaving any remaining foliage.

Ensure there is light and air around it and give it a good soaking of water.

Your Delphinium should regrow another flowering spike towards the end of August, for a second display in September.

Are Delphiniums good for bees?

Yes, Delphiniums provide nectar and pollen for many pollinators, but particularly bumble bees.

Bumblebee on a delphinium

Are they frost hardy?

Yes, Delphiniums are hardy, with an RHS hardiness rating of H5 to H6, even in a severe winter, if they are grown in free-draining soil and a sunny spot.

Plants in containers are more susceptible to cold, as their roots are less insulated than they would be in the ground.

What colours do Delphiniums come in?

Delphiniums are best known for their vivid sapphire blue flowers. A good example is Delphinium ‘Amadeus’.

They also come in mauve, pink, red, and white.

Blue delphiniums
Mauve delphiniums
Pink delphiniums
Red delphiniums
White delphiniums

Do they need a lot of water?

Yes, newly planted Delphiniums need watering regularly during their first summer to keep the soil around the roots moist. Water every few days if the weather is hot and dry.

Do they need staking?

Medium to tall plants, of 1.2 metres or more need support. Push at least three twiggy stems into the ground, evening spaced around the clump.

You can also use metal supports with a grid through which the stems can grow.

Put them in place before new growth reaches 30 centimetres high. For taller flower stems, insert a strong cane into the ground.

Do Delphiniums make good cut flowers?

Yes, they make wonderful additions to a floral arrangement, looking lovely in vintage displays, and after cutting can last up to a week in a vase.

Aim to cut them once most of the flowers have started to open, at a 45-degree angle.

A great method to help them stay healthy for longer is to fill the hole in the long stem with water by submerging it, then when holding your thumb over the hole, lower them back into the vase. This keeps them healthier and standing upright for longer. Change the water every two to three days to keep them fresh.

Delphinium petals can make a lovely feature when dried too, retaining some of their colour for a lovely pastel effect, which produces a great flower confetti for many different events. Dry out fresh petals on a baking try somewhere warm, turning regularly, and then store in an air-sealed container.

Cut flower delphiniums

Do Delphiniums need deadheading?

Yes, you can remove the faded flowers from the spike to stop them from going to seed, saving the plant energy for more flowers. Just carefully hold the spike, and remove the flowers with secateurs as close to the base where it attached to the plant as possible.

You could also pinch the flowers off if you would prefer. Do this between July and October continually as the individual flowers fade.

Otherwise, just cut down faded flower spikes of perennial Delphiniums at ground level to encourage a further flush of flowers.

Do Alliums need feeding?

Apply feed early in the spring when they are actively growing and preferably before blooming. A granular all-purpose fertiliser is good choice. You can also apply an eggshelll feed, using crushed eggshells and water. Steep the shells for a few days and it will supply calcium, which is essential for bulb development. If you want to apply a liquid feed, it will offer a fast-acting option as the feed is absorbed by the plant as it draws water. Mulching and regular watering will complement your feeding routine.

What do you plant with Delphiniums?

To achieve a cottage-style flower bed, grow Delphiniums beside peonies, chrysanthemums, alliums, dahlias, foxgloves, and lupins. This will also help with successional flowering for consistent bright colours throughout the seasons.


When to cut back Delphiniums?

An early flowering perennial, Delphiniums should be cut near to ground level after the first flush of flowers to encourage fresh foliage and a second flush of flowers in late summer.

If you don’t cut them back after the first flowering, you risk losing the chance of a second flush later in the year.

These should then be cut back again in autumn or spring.

How to divide Delphiniums?

Perennial Delphiniums can be divided in spring, by separating mature clumps into two or four pieces. You can discard the woody centre, and plant these divided clumps as individual plants, which you should see flowering the same year.

When do they start to grow back?

Delphiniums should start to grow back during the UK spring.

Do Delphiniums self-seed? Will Delphiniums self-seed?

They do often self-seed but the product won’t be exactly like the parent plant, thanks to cross-pollination with other Delphinium plants.

What are the common problems with Delphiniums and how do I fix them?

Powdery mildew on a leaf

Powdery Mildew

Delphiniums can be susceptible to powdery mildew in dry weather, so it’s important to keep the soil around them moist. These plants spread rapidly, competing for space, and the overcrowding stops air circulation. This can also lead to powdery mildew and the spread of other fungal and bacterial diseases. You can alleviate this by thinning and dividing in early spring.

Rust on a leaf


They can also be affected by rust. This causes rust-coloured pustules on the foliage.

Simply pick off any affected leaves as you see them and clear up any fallen leaves you find in autumn.

Black blotch on a leaf

Delphinium Black Blotch

Delphinium black botch is a bacterial infection that causes large black blotches on leaves. It’s particularly common during wet summers and can affect the health of the whole plant.

All you can do is remove the affected plants to stop the disease from spreading, and avoid planting delphiniums back into the same spot.

How do I stop slugs and snails from eating my Alliums?

The other common pest to keep an eye out for are our old friends the slug and snail. Now they do have an important part to play in the ecosystem, but we want them to be focussed materials we don’t want, rather than our prize blooms.

The best things to do include:

  • Avoid watering at night.
  • Encourage birds into the garden.
  • Use grit or crushed eggshells to create a barrier that is uncomfortable to travel over.
  • Use copper tape around your pots and containers.
  • Plant a beer trap – not too much, just enough to attract them, and sit the trap just proud of the soil so beneficial insects such as ground beetles don’t fall into it.

What are the common pests for Delphiniums?

Caterpillars can be quite fond of Delphiniums, so deterring them will help to keep your Delphiniums looking fresh. Spraying regular soapy water onto any affected plants can make the surface slippery, which will give caterpillars a difficult time climbing up your plants.

Slugs and snails are also common pests of Delphiniums.

Are they deer-resistant?

Yes, Delphiniums are deer resistant. And they are also rabbit resistant so you don’t need to worry about these woodland creatures nibbling away at your Delphiniums.

Why are my Delphiniums drooping?

The likeliest cause of drooping Delphinium flowers is that they have been underwatered. Make sure you regularly water them during periods of drought to keep them standing tall.

Providing some light support may also be helpful, as this plant has hollow stems, which when combined with heavy flowerheads can mean the weight causes the stems to droop or even snap.

Why are my Delphiniums dying?

This could be down to several different causes. Delphiniums which have been left to sit in the cold and wet of winter may struggle to return the following year or may die as a result, so ensuring they have ample drainage and mulching over winter should provide the right conditions to help them through the season.

Considerable slug attacks whilst the plant is still young may leave these vulnerable plants unable to recover too, so try to stay vigilant with your slug control measures until the plant is stronger and more established.

Another possible cause could be the bacterial disease Delphinium black blotch.

Are they poisonous to humans?

Yes, both the plant and its seeds are poisonous for humans and animals. If consumed, they can lead to severe illness, paralysis, and even death.

The lovely pompom blooms of Alliums create wonderful interest in garden borders. If you have any questions about this or any other plants you want me to do a video on, please subscribe to my YouTube channel and leave a comment below one of my Google Questions videos.

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