DELPHINIUMS: HOW TO GROW & CARE FOR PERENNIAL DELPHINIUM

DELPHINIUMS: HOW TO GROW & CARE FOR PERENNIAL DELPHINIUM

Flower garden with Pacific Giant hybrid delphiniums. Photo by: John Glover / Alamy Stock Photo.

Delphiniums bring unrivaled height and color to summer gardens with their showy spikes of vibrant flowers. The most common colors are shades of blue or purple, but there are others available. They bloom with single, semi-double or double flowers, also called florets.

Delphiniums can be high-maintenance, needing just the right conditions. They prefer cool, mild summers with low humidity. Plant them in a spot with adequate moisture and well-draining soil. Thankfully, new strains of hybrids are being developed that aren’t as fussy.

On this page: The Basics | How to Plant | Care | Delphinium Pictures | Landscape Design Tips | Cutting and Arranging | Delphinium Alternatives

  • DELPHINIUM BASICS
  • PLANTING DELPHINIUMS
  • DELPHINIUM CARE
  • DELPHINIUM PICTURES
  • LANDSCAPE DESIGN TIPS
  • CUTTING AND ARRANGING DELPHINIUMS
  • ALTERNATIVES TO GROWING DELPHINIUMS

DELPHINIUM BASICS

Zones:

3-7; better planted annually in warmer climates.

Height/Spread:

Varies by type. The tallest varieties are found within the Delphinium elatum group, with stalks regularly 5 to 6 feet tall (with some reaching 8 feet) and a spread of 2 feet. The D. belladonna group averages 3 to 4 feet tall with a spread of 2 feet. Dwarf varieties, like D. grandiflorum, range 1 to 2-feet tall and 12 to 18 inches wide.

Exposure:

Delphinium plants require 6 to 8 hours of sun a day, and gentle morning and early afternoon sun is preferred. The roots need cool, moist shade.

Bloom Time:

Summer (June - July)

Color:

Delphiniums bloom in a wide array of colors including true blues, purple, lavender, pink, scarlet, white, and rarely yellow. Small flower centers are called ‘bees’ and may be white, tan, brown, black or striped.

Types:

The most popular delphiniums belong to the D. elatum, D. belladonna, D. grandiflorum and hybrid groups.

  • Elatum Group: This clump-forming perennial blooms with numerous single, semi-double, or double flowers in early to mid-summer. Flowers to 2-1/2 inches across fill stalks that are commonly 5 to 6 feet tall. Growing this variety may not be for the beginning gardener, as they are fairly high maintenance.
  • Belladonna Group: This upright perennial grows flower stalks that bloom with branched spikes of single or double, 1 to 2-1/2 inch flowers. Belladonnas are comprised primarily of hybrid crosses of D. elatum and D. cheilanthum and range 3 to 4 feet tall.
  • Grandiflorum Group: Also called Chinese or Siberian delphinium, this variety has a compact, bushy habit and grows 1 to 2 feet tall and nearly as wide. Grandiflorums bloom blue or white flowers mid-summer and tend to have a higher heat tolerance than other delphinium species.
  • Pacific Giants: The Pacific hybrids, also known as Pacific Giants, can grow up to 4-6 feet tall and include popular cultivars like 'Black Knight', 'Galahad', 'King Arthur', 'Blue Jay' and 'Blue Bird'.
  • New Zealand Hybrids: The New Zealand hybrids are medium-sized, and include such favorites as 'Pagan Purples', 'Dasante Blue', and the New Millennium series.

Toxicity:

All delphiniums are considered toxic and parts of the plant and flower may cause severe discomfort to humans and animals if ingested. Gloves and long sleeves should be worn when working with delphiniums, as contact with the foliage can result in skin irritation.

Other:

Delphiniums attract pollinators such as bees, butterflies and hummingbirds; resistant to deer and rabbits.

PLANTING DELPHINIUMS

When to plant:

Plant potted delphiniums in the spring.

Where to plant:

Delphiniums should be planted in an area that receives 6 to 8 hours of sun per day, preferably morning sun. They need shelter from strong winds and rain downpours to avoid damage to the tall flower stalks. Standing water causes crown and root rot, so a well-drained site is a must. To prevent disease, plant in an area that allows good air circulation and where they’re not overcrowded.

How to plant:

Prepare the planting site with organic matter or compost to 1 foot deep. Plant delphiniums in a hole that is twice the diameter of the container and backfill with soil that has been well-mixed with the organic matter. The top of the rootball should be level with the soil.

DELPHINIUM CARE

Delphinium flower stalks supported by stakes. Photo by: Malgorzata Larys / Alamy Stock Photo.

Pruning:

For best flowering, new plants should be thinned to 2 to 3 good shoots when they are 3 inches high. Established plants can be thinned to 5 to 7 of the best shoots. Cut the main stalk down after flowering to the level of its smaller side shoots, which will bloom secondarily with slightly smaller flowers. To encourage a second, but smaller, bloom in late summer or early autumn, cut the stalks to the ground just after flowering. Prune the entire plant to the ground after it wilts in autumn.

Soil:

Well-drained, humus-rich soil is a must, preferably slightly alkaline. Although mulch helps preserve moisture in the soil, if it is applied too closely to the stems it can cause them to rot. For finicky delphiniums, soil quality plays a major role in success or failure.

Amendments & fertilizer:

Apply a balanced, slow-release liquid fertilizer every 2 to 3 weeks. Avoid high-nitrogen fertilizers. Composted manure applied in autumn helps supplement these heavy feeders.

Watering:

Water deeply during rainless periods, but don’t allow standing water. Delphiniums like it moist, but water that lingers causes crown and root rot. Water delphiniums at the base, keeping the foliage dry to help prevent disease.

Propagation:

According to the National Garden Bureau, September to March is the best time to seed delphiniums. Use fresh seeds, as germination can be poor after a year. Presoaking is recommended to improve the germination rate, along with temperatures of 65 at night and 75 during the day while germinating. Cover seeds with only one-eighth inch of soil and keep evenly moist, but not wet as this can cause them to rot. Smaller rather than larger tray size is also recommended. Transplant after plants have two true sets of leaves.

It is common for delphiniums not to bloom the first year, so be patient and you should see them come to life in the second year. Seeds collected from hybrids growing in the garden may not produce offspring that bloom true to color.

Diseases and pests:

Delphiniums are susceptible to a host of diseases including powdery mildew, Southern blight, bacterial and fungal spots, gray mold, crown and root rot, rust and others. Planting your delphiniums in a well-ventilated area and keeping the foliage dry will go a long way in preventing disease. Care should be taken to protect young plants from snails and slugs, as they can cause considerable damage. Delphiniums are also commonly plagued by cyclamen mites, aphids and nematodes.

If your delphiniums are performing poorly, the book Essential Perennials offers these tips:

  • Black spotted foliage can mean cyclamen mites.
  • Curled & distorted leaves usually indicate aphids.
  • Yellow foliage and stunted growth may be caused by nematodes (this can also be from a lack of fertilizer).
  • Black, foul-smelling decay at the base is bacterial crown or root rot caused by poor drainage.
  • Disfigured stems and foliage along with stunted growth can be a sign of powdery mildew.

Support:

Other than the dwarf varieties, delphiniums require staking. Their hollow stems will break when blown in the wind or when the flowers become weighed down from rainfall. Stake them with sturdy supports and attach at 12- to 18-inch intervals.

DELPHINIUM PICTURES

Swipe to view slides

Photo by: Walters Gardens, Inc.

Delphinium elatum ‘Million Dollar Blue’
(Million Dollar Series)

Zone: 3-7

Height/Spread: 2-1/2 to 3 feet tall, 18 to 24 inches wide

Exposure: Full sun

Color: Shades of blue

Semi-double to double flowers, improved heat tolerance

Photo by: Dowdswell’s Delphinium Ltd / Courtesy of Walters Gardens, Inc.

Delphinium elatum ‘Black Eyed Angels’
(New Millenium Series)

Zone: 3-7

Height/Spread: 3 to 5 feet tall, 18 to 24 inches wide

Exposure: Full sun

Color: White flower with black bee

Improved heat tolerance, magnificent when planted en masse

Photo by: Dowdswell’s Delphinium Ltd / Courtesy of Walters Gardens, Inc.

Delphinium elatum ‘Pink Punch’
(New Millenium Series)

Zone: 3-7

Height/Spread: 3 to 5 feet tall, 18 to 24 inches wide

Exposure: Full sun

Color: Mulberry pink, with white, brown or pink-striped bee

Improved heat tolerance, strong stems, and a vigorous grower

Photo by: Rock Giguere / Millette Photomedia.

Delphinium xbelladonna ‘Delft Blue’

Zone: 3-7

Height/Spread: 3 feet tall, 12 to 18 inches wide

Exposure: Full sun

Color: Light blue

Unique two-toned, single flowers

Photo by: Garden World Images, Ltd / Alamy Stock Photo.

Delphinium grandiflorum ‘Blue Mirror’

Zone: 3-7

Height/Spread: 2 feet tall, 18 inches wide

Exposure: Partial to full sun

Color: Violet-blue flowers

Shorter variety, reliable bloomer

Photo by: Garden World Images, Ltd / Alamy Stock Photo.

Delphinium ‘Black Knight’
(Pacific Hybrid)

Zone: 3-8

Height/Spread: 4 to 6 feet tall, 18 to 24 inches across

Exposure: Full sun

Color: Purple

Excellent flower and stem quality, good for cut flowers

Photo by: Holmes Garden Photos / Alamy Stock Photo.

Delphinium ‘Galahad’
(Pacific Hybrid)

Zone: 3-8

Height/Spread: 5 to 6 feet tall, 12 inches wide

Exposure: Full sun

Color: White flower, with white bees

Large, semi-double blooms attract bees, butterflies and hummingbirds

Photo by: Steffen Hauser, botanikfoto / Alamy Stock Photo.

Delphinium ‘Pagan Purples’

Zone: 3-7

Height/Spread: 4 to 6 feet tall, 18 to 24 inches wide

Exposure: Partial to full sun

Color: Blue-purple flowers, with white or brown bees

Proven vigor, strong stems, good for cut flowers

LANDSCAPE DESIGN TIPS

  • Delphiniums are a popular choice for cottage-style gardens.
  • Grow tall delphiniums at the back of a mixed border or as a centerpiece to an island flower bed for vertical accent.
  • For the best show, plant delphiniums in groups or massed.
  • Plant up against a fence for added support and wind protection.
  • Joe Pye weed, hyssop and salvia make good garden companions.

CUTTING AND ARRANGING DELPHINIUMS

Follow these helpful tips for using delphiniums as cut flowers:

  • Cut delphiniums at a 45-degree angle when many of the flowers are already open.
  • Rinse the stems well before putting them in the vase.
  • Remove any foliage that will be underwater to help keep the water clean.
  • Freshen the cut ends of the stems and change out the water every 2 to 3 days.
  • Display the arrangement in a cool location, out of direct sunlight.

ALTERNATIVES TO GROWING DELPHINIUMS

Many gardeners steer clear of growing delphiniums in their garden because of their high-maintenance needs. If you’re not up for the challenges of growing delphinium flowers but still want the look of tall flower stalks, you might consider one of these alternatives:

  • Annual larkspur (Consolida ajacis)
  • Gladiolus
  • Foxglove
  • Hollyhock
  • Baptisia

RELATED:
Color in the Garden
21 Blue Flowers for Your Garden
Summer Garden Ideas


Delphinium Winter Care: Preparing Delphinium Plants For Winter

Delphinium is a stately plant with tall, spiky blooms that beautify the garden in a big way during the early summer months. Although these hardy perennials are easy to get along with and require a minimum of care, a few simple steps will ensure they survive winter cold unscathed.


About Delphinium Plants

One commonly thinks of delphinium plants (Delphinium) as having true blue flowers, which is the most common color. But numerous hybrids are available in shades of pink, lavender, red, white and yellow. Blooms may be single or double.

Delphinium planting is normally at the back of the bed, where flower spikes can reach 2 to 6 feet (.6-2 m.) tall. Delphinium flowers are often planted in masses or groups. Shorter varieties are useful in other areas of the garden.


What You’ll Learn

The most popular explanation for the name “delphinium” is that ancient Greeks (in 700-480 BC) thought the unopened buds with their telltale spurs resembled a dolphin’s nose.

In ancient Greek, “dolphin” translates to “delphínion.” It’s easy to see how “delphinium” emerged from the word.

The flowers have been grown and cultivated in gardens since at least the 16th century.

I confess that when I first planted my three delphiniums, I called them larkspur. I have always loved the cheeriness of that word and wanted that to be their name.

To disentangle the nomenclature of these elegant blooms, let’s start with the Ranunculaceae family, of which buttercups, clematis, monkshood, and columbine are also members.

The five largest genera in the family Ranunculaceae are: Ranunculus, Delphinium, Thalictrum, Clematis, and Aconitum. But there are also Consolida, Helleborus, and over 30 others.

It’s commonly thought that annual larkspur was once included in the Delphinium genus.

But larkspur’s classification into the genus Consolida was recognized as early as 1965, according to a 1967 article by Philip Munz in the Journal of the Arnold Arboretum, published by Harvard University.

Still, many gardeners refer to both true delphiniums and true larkspur by the name “larkspur.”

Under the USDA’s classification report listing for the genus Delphinium, you’ll see it listed as the genus for all plants with the common name “larkspur” – and Consolida is saved for plants with the common name “knight’s-spur.”

It’s all rather perplexing. And to make things worse, the plants look like twins, or at least lookalike sisters.

Both plants feature heavily lobed leaves that cluster at the bottom of upright spiked columns bearing dozens of blooms.

But if you study them closely, they have two noticeable differences:

  1. True delphiniums are short-lived perennials, while larkspur are annuals.
  2. Delphiniums tend to have larger, more densely clustered blooms, whereas larkspur are more delicate and spaced further apart.

Common perennial delphinium species include D. elatum, D. grandiflorum, and D. chelianthum.

We’ll take a quick look at the common botanical groupings that have arisen from these species in a moment.

One thing both flowers have in common is that every part of them is toxic to humans and animals if ingested.

This is true of many flowers in the buttercup family, but as long as you keep your young children and pets from eating them, you can enjoy their beauty without fear.

Plus, they’re said to taste bitter and acrid. Not exactly light snacking material.


Delphiniums need cool, moist climates to survive. They will fail to grow well in climates that have hot, dry summers, according to the Old Farmer's Almanac. Gardeners who live in areas like the Pacific Northwest, which features cool, wet springs and summers, will be best able to grow these plants. Gardeners In USDA zone 8 have some success with the plants as well, as long as they are planted where they receive afternoon shade. Gardeners who live in warmer growing zones, such as those above zone 7, should plant their delphiniums where they will be protected from hot, direct sunlight, and where the soil is shaded. Although the flowers don't thrive in growing zones higher than USDA zone 8 -- such as in parts of California and most of the southern part of the United States -- they can still be grown they will just be short-lived.

Soil is as equally important to consider as the climate. Delphiniums prefer rich, alkaline soil. To give them a boost, spread a mixture of equal parts lime and wood ashes around the flowers in the spring. Consistently moist, cool soil is best -- about an inch per week is required -- although too much water may cause rot diseases to develop. Stem and crown rots are common, as are fungal diseases of the leaves, so water at the ground level if possible to avoid letting water sit on the leaves. If you live in USDA zones 3 through 7, plant your delphiniums in full sunlight, which will help prevent fungal problems.


How to Grow Blue Butterfly Delphiniums

Related Articles

Blue Butterfly delphinium (Delphinium grandiflorum "Blue Butterfly") brightens the landscape with distinctive blue blooms from late spring through early summer. While some types of delphinium reach impressive heights of up to 6 feet, Blue Butterfly delphinium is more diminutive, topping out at 12 to 18 inches. Blue Butterfly delphinium is appropriate for growing in Sunset's Climate Zones A1 through A3, 1 to 10 and 14 through 24.

Water delphiniums to keep the soil moist but never soggy. As a general rule, delphinium benefits from 1 inch of water every week throughout the summer, either from rain or supplemental irrigation. Never allow the soil to become completely dry.

Water delphinium at the base of the plant and keep the foliage as dry as possible. Delphinium is susceptible to mildew, rot and other problems caused by damp conditions.

Apply 3 to 4 inches of an organic mulch, such as compost or shredded bark. Mulch delphiniums during warm weather to keep the roots moist and cool.

Fertilize delphiniums every two to three weeks, using a general purpose liquid fertilizer. Refer to the instructions on the container for specific information regarding rate of application.

Deadhead, or remove each blossom as soon as it wilts, to prolong blooming and keep the plant neat. To deadhead delphinium, use your fingernails or garden pruners to remove the spent bloom and stem down to the point where you see a new bud, flower or leaf.

Cut delphinium stalks to the ground in late summer or early autumn. Spread a fresh layer of mulch around the plant to insulate the roots for the coming winter.


Delphinium Companion Plants

Depending on variety, delphinium plants can grow 2- to 6-feet (.6 to 1.8 m.) tall and 1- to 2-feet (30 to 61 cm.) wide. Oftentimes, tall delphiniums will need staking or some kind of support, as they can get beaten down by heavy rains or wind. They can sometimes become so laden with blooms that even the slightest breeze or little pollinator landing on them can seem to make them topple over. Using other tall border plants as delphinium plant companions can help shelter them from winds and rains while offering additional support too. These may include:

If using stakes or plant rings for support, planting medium height perennials as delphinium companion plants can help hide the unsightly stakes and supports. Any of the following will work well for this:


Delphinium

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Delphinium Plant Features

The tall, stately blooms of delphinium have played a starring role in perennial borders for generations. With towering flower stalks of blue, white, lavender, or pink blooms, delphiniums are a delight in the back of a garden border. Tall delphinium varieties can stretch 6 feet tall, but there are also more compact varieties that grow just 2 feet high. Delphiniums are also beloved by bees and butterflies, which feast on the nectar-rich flowers. Delphiniums also make wonderful cut flowers. Hardy from zones 3-8.

Delphinium Questions?
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Delphinium Growing Instructions

Delphinium grows best in a sunny location with rich, slightly moist soil. Some varieties grow best in cooler, milder regions of the country, but there are delphiniums that thrive in any sunny situation as long as they aren't subjected to super hot temperatures in midsummer. If you're in an area with especially hot, humid summers, delphiniums do best in a situation with morning sun and afternoon shade --- as well as a 2- to 3-inch-deep layer of mulch over the soil.

Taller delphinium varieties also require staking to keep them from toppling in windy weather. Feed with a slow-release granular fertilizer in the early spring and never let the plants dry out completely. Amending the soil liberally with compost at planting time can be particularly helpful to delphiniums, especially if you have poor soil. In areas with heavy clay, topdressing the soil with a layer of compost every year can also be extremely beneficial.


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