How to Grow and Care for Delphiniums (Delphinium spp.)

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Delphiniums are a group of around 365 plants that belong to the genus Delphinium, and the buttercup family Ranunculaceae. Sometimes mistakenly referred to as larkspurs, delphiniums, although similar, are actually different plants altogether! Plants in this group consist of annuals, biennials, and perennials. 

The most common delphiniums grown today are part of or derived from the hybrid groups Delphinium x elatum, Delphinium (Belladonna Group), and Delphinium (Pacific Hybrids). They are perennials that will bring color to the garden year after year, however, the pacific hybrids are usually grown as annuals or biennials. These wonderful plants have showy flowers that look fantastic in cottage-style or English-style gardens. 

History

Native to the Northern Hemisphere, delphiniums have been cultivated as early as 1578. Today, it is uncommon to see straight species sold on the market, as the well-known and extremely popular delphinium flowers are the results of heavy hybridization between a wide range of species and groups. 

The genus name Delphinium is derived from the Greek word “delphis” which means dolphin. This is in reference to the bud shape on some species supposedly resembling a dolphin! In England, they are nicknamed “Queen of The Border” due to their popularity as border plants. 

These lovely flowers require some maintenance, but produce long racemes or spikes which are densely packed with the most beautiful blooms, many of which will attract butterflies and other pollinators into the garden! 

They may have single or double flowers that come in a wide range of colors including white, pink, blue, purple, yellow, and occasionally red. They are firm garden favorites that are heavily featured in gardens time and time again!

Plant Facts

Scientific nameDelphinium spp.
Common namesDelphinium x elatum, Delphinium (Pacific Hybrids), Larkspur, Candle Larkspur, Delphinium Elatum Group, Queen of The Border, Delphinium (Belladonna Group)
GenusDelphinium
FamilyRanunculaceae
Height3 ft. 0 in. – 8 ft. 0 in.
Width2 ft. 0 in. – 3 ft. 0 in.
USDA Plant Hardiness Zone3 – 7
OriginNorthern Hemisphere
Flower colorsWhite, Pink, Blue, Purple, Red, Yellow
Blooming seasonJune – July
Plant/Flower special featuresCentral spikes with showy flowers

How to Plant Delphiniums

Delphiniums can be grown both in beds and containers. Before planting, it is important to take into account the variety. Some delphiniums may grow as tall as 6 feet and therefore should be positioned at the back of the display, whereas some smaller varieties will be more suitable for container planting and can be placed in the middle. Choose a site with sufficient light that is sheltered from strong winds. 

These plants can be planted at any time as long as the soil/compost isn’t waterlogged or frozen, or if they can be adequately watered during dry periods. However, planting during spring or early summer is recommended. Depending on the variety, space them between 1 and 3 feet apart. 

Growing Delphinium Flowers in Beds

Before planting, de-weed the area and improve the soil by mixing in well-rotted manure or garden compost. Gently tip out the plants from their container and tease the roots apart with the utmost care. This will encourage the roots to spread into the ground in the area surrounding the hole.

Dig a hole wide enough and deep enough to comfortably house the root ball. Place the plant inside so the base of the stems or shoots are just above the ground, cover with soil and press down firmly. Water well to settle in.

Growing Delphinium Flowers in Containers

Choose a container that is large enough to house the plant’s root ball and has adequate drainage holes. For plants that will be left outdoors year-round, terracotta pots are the best choice. Use loam-based compost and mix in some perlite or grit to improve drainage. 

Carefully remove the plant from its old container and gently tease the roots. Plant the root ball in line with the compost surface. Press down the compost to eliminate any air pockets and water well to settle in. Top up the compost if necessary. Make sure the top of the soil line is at least 1-inch below the top of the container to allow room for the water to soak in. 

How to Propagate Delphiniums

Delphiniums can easily be propagated from seeds, by division, or from cuttings. Just bear in mind that they are toxic, so always wear protective gear while handling them. 

Propagation from Division

By far the easiest and most popular method of propagating delphinium plants is through division. Plants will need to be dug up and divided every 2-5 years to prevent overcrowding. This makes it the perfect opportunity to create more plants while discarding the older ones and maintaining a healthy garden bed!

In spring, use a garden fork to gently lift out the delphinium plants from the soil. Take care to damage the roots as little as possible, and gently shake off any excess soil so the roots can be seen clearly. Delphiniums have woody crowns, therefore a sharp knife of spade may be required to cut the root into sections. 

Divide the clump into 2-4 sections, each containing 3-5 healthy shoots, and discard the woody center. Plant the clumps back into the ground following the guidelines for bed planting. Expect the new plants to flower in the same year. 

Propagation from Cuttings

Take basal softwood cuttings in spring, by using a sharp, clean knife to cut off 3-4-inch long, study shoots as close to the base as possible. Shoots may have woody tissue at the base. 

Remove any lower leaves and pinch out the soft tip before dipping the end in rooting hormone (liquid or powder), and place it in a tray of perlite or rooting compost. Keep the tray in an area with bright, indirect light, at 60°F and cover with a plastic bag to keep the humidity levels high. Keep the rooting medium moist but not overly wet, and twice-weekly remove the plastic covering for 10 minutes to allow ventilation. 

Within 10 days the delphinium cuttings should be rooted and will be ready to be potted in individual containers. Plant them out once they are firmly established.  

Propagation from Seeds

Some delphinium cultivars can also be raised from seeds. Either buy seed packets from nurseries or online or use collected seeds from the garden. Plants from the Pacific Hybrids or Magic Fountain Series work particularly well but bear in mind that offspring may not be true to the parent plant. 

When growing delphiniums from seeds, always try to use fresh seeds as viability declines year after year, so germination rates in older seeds may be poor. 

Sow seeds in Spring in a small tray/pot of evenly moist seeding mix and cover with a thin layer of soil. Pre-soaking the seeds before sowing is optional, but it may increase the germination rate by 20-30%. Keep the tray at a temperature of 55°F, and expect germination within 14 days. 

Once seedlings have their first set of true leaves, they will be ready to be transplanted out onto the garden bed or into their container. Expect flowering around 18 months after sowing. 

Care and Maintenance

Here is some advice on caring for your delphiniums:

Soil

Grow delphiniums in fertile, well-draining soil. Plants will not survive over winter in poorly drained soils or soils that remain permanently wet.

Water

Newly planted delphinium flowers will require regular watering over the summer to ensure their roots are kept moist while they are becoming established. During extremely hot and dry spells, watering may be required every few days.

Once established, these plants prefer moist, but not overly wet soils. Watering once a week should be adequate.

Container-grown plants will require more regular watering to prevent the soil from drying out. During dry periods this can be needed as often as every day. During the winter watering may need to be reduced. 

Fertilizer

Delphiniums are heavy feeders and will need fertilizing every week using a potassium-rich, liquid fertilizer. This should be done following the package instructions, from when the first flowers appear until the end of August. Regular feeding will help to maintain bigger and better blooms. 

During spring, spread a 2-inch layer of mulch (either garden compost or well-rotted manure) around the outside of the clumps to help preserve moisture. 

Yellowing foliage and stunted growth may be signs the delphinium plants need additional feeding. 

Sunlight

Plants need to be in a position where they receive full sun because they flower poorly in shade.

Temperature and Humidity

Delphinium flowers are suitable for USDA zones 3-7 and prefer short, cool, summer temperatures as opposed to long, hot summers. 

Pest and diseases

Delphiniums don’t have too many problems, but things to watch out for are slugs and snails, particularly on new growth, and leaf miners and caterpillars. 

The foliage is susceptible to powdery mildew. This is often caused by environmental stress, such as overly dry conditions or if the plants are being grown in shady areas. 

Delphinium Black Blotch is also something to keep an eye out for, this is a non-fatal disease, but causes unsightly brown-black blotches on leaves and occasionally stems and flowers. Heavily infected plants will have stunted growth, and leaves with heavy blotching can turn brown and shrivel up. 

If plants become infected, remove and dispose of them and discard any collected seeds. Do not plant replacement delphiniums in the same spot, choose a fresh site for planting. 

Pruning

Deadhead faded flower spikes to ground level to encourage more flowering. Old foliage can also be cut back after the first frost has passed to keep the border looking tidy. 

It is possible to thin out the emerging shoots on mature delphinium plants in spring to promote taller flower spikes. Select the 5-7 strongest-looking shoots to keep.

Plants that will grow over 4 feet tall will require support to stop their stems from falling over. Stake them using 3 canes spaced evenly around the clump with soft twine wrapped around the canes to form a supportive triangle. Metal supports with a grid system are also suitable.

Particularly tall varieties may need staking on each flower stem using a strong cane and adding soft twine around the flower spike as it grows. Select a cane as tall as the final height of the flower spike. Stakes and support should be put in place early in the growing season to prevent damage to growing roots later on.

Overwintering

Delphiniums are winter hardy down to USDA zone 3 and if grown in well-drained soils should be able to withstand the colder temperatures. However, container-grown plants are more fragile to the cold as their roots are less insulated. 

Container-grown delphiniums should be moved to a sheltered spot to protect them from harsh winds and rain over winter. Move them next to a wall, into a greenhouse, or into a cold frame to lessen the risk of root rot and provide winter protection. 

Toxicity

Delphiniums contain delphinine alkaloids and other substances that make them poisonous and potentially fatal to both people and some animals if eaten. Symptoms include burning of the lips and mouth, throat numbness, diarrhea and vomiting, muscular spasms and weakness, convulsions, and respiratory system paralysis.

Foliage may also cause skin irritation, so wearing gloves and thoroughly washing hands after handling is recommended. 

Uses of Delphiniums

Delphiniums are most commonly used as garden ornamentals and are extremely popular for adding height to beds and borders! They are an excellent choice for cottage-style gardens, and many varieties make wonderful cut flowers that can last 6-8 days in a vase. 

The roots of some Delphinium species have been used in traditional medicine as a treatment for ailments such as headaches, toothaches, epilepsy, paralysis, and more. However, the similarity of species often results in a mix-up between toxic and non-toxic plants resulting in accidental poisoning. 

Common Varieties and Cultivars

There are so many lovely varieties of delphinium flowers to choose from, here are some of the most popular cultivars:

  • Can-can – This bold delphinium flower may reach up to 59 inches tall and has double flowers that grow just under 3 inches wide. Blooms are violet with darker petal edges, and the outermost petals have royal blue petal edges.
  • Cinderella – Cinderella is a beautiful delphinium variety that would look lovely in cottage-style garden borders! It grows to just under 4 feet tall and has delicate pale pink double flowers. Blooms have white centers and green central eyes.
  • Faust – Faust has deep, purple-blue, semi-double flowers with dark central eyes. It reaches heights of 70 inches and is the perfect choice to add some rich color to cottage-style or informal gardens!
  • Langdon’s Royal Flush – This delphinium flower would be a great choice for bringing color to city gardens! It grows as tall as 59 inches and has racemes that are densely packed with raspberry pink, semi-double flowers that have dark pink veining and white central eyes. 
  • Sunkissed – A fantastic variety for cottage-style gardens, this plant would look delightful growing along a garden fence! Growing as large as 59 inches, Sunkissed has creamy white, semi-double flowers with pale yellow central eyes. 

Conclusion

There are around 365 delphinium species in the genus Delphinium, which is a part of the buttercup family, Ranunculaceae. Many of the most popular garden varieties belong to the groups Delphinium x elatum, Delphinium (Belladonna Group), and Delphinium (Pacific Hybrids) which are perennials, however, some are grown as annuals or biennials. 

They are native to the Northern Hemisphere, but straight species are not as common in garden centers and nurseries as their much-loved hybrids. Many delphinium hybrid cultivars are easily available today in a range of colors and heights, making these plants a top choice for beds and borders.

Although they require a little maintenance, this doesn’t stop them from being firm favorites for cottage-style gardens and wonderful additions to any garden!

Up next: Delphinium Flower Meaning and Symbolism

~ image source: depositphotos/audiznam