If you fancy yourself a cut flower garden aficionado, then look no further than the lovely delphinium. These flowers grow on tall, upright spikes and make a beautiful addition to any cutting garden. They begin to bloom in early summer, and you can get a second flush of flowers blooming into the late summer and into the fall.
Delphiniums can grow up to 4 feet tall, so be sure to plant them in an area where they can get full sun without shading out other plants. Pacific hybrids are not as tall if you’re looking for a plant that is a little more compact for a smaller space. The same goes for Chinese delphinium, which grows to be about 1 foot tall.
However, they are toxic to the touch and livestock and pets if ingested. So be sure to plant delphiniums in an area not readily accessible to pets and/or small children. Many different varieties and hybrid plants are available, and all of them attract pollinators to the garden.
Big fuzzy bumblebees seem to especially favor the tall flower spikes of delphiniums, perhaps because the stalks are big enough to hold their weight. Many gardeners love planting delphiniums to help increase the biodiversity available in the garden to these important insects. They’re mostly known for their deep blue flowers but also come in a range of different colors.
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Quick Care Guide
A beautiful stand of delphinium flowers. Source: Paul Gulliver
|Common Name||Delphinium, larkspur|
|Scientific Name||There are over 300 delphinium species.|
|Height & Spread||Up to 4 feet tall and 2-3 feet wide|
|Light||Full sun, 6-8 hours per day|
|Soil||Fertile, rich, moist soils|
|Water||Water deeply once a week|
|Pests & Diseases||Slugs and snails, cyclamen mites, bacterial and fungal spots, powdery mildew, gray mold, white rot, root rot, southern blight, leaf smut, white smut|
All About Delphinium
There are many different types and hybrid varieties of Delphinium under a wide range of scientific names. Delphinium elatum and Delphinium grandiflora are the most popular. They are also sometimes referred to as larkspur, although true larkspurs are in the Consolida genus.
Delphiniums are known for their tall, upright, showy spikes. These flower spikes come in a range of colors, from light blue, pink, purple, and white. As mentioned above, delphiniums are toxic to the touch and can cause severe skin reactions. For this reason, be sure to wear gloves whenever you are working with or near them.
It’s also recommended that you plant delphiniums in an area not easily accessible to small children and/or pets. If ingested, it can lead to severe paralysis or death. Despite its toxic traits, delphinium flower stalks were used by Native Americans to make blue dye. In ancient times it was used to repel scorpions, lice, and other parasites.
Types of Delphinium
A closeup of delphinium. Source: KingsbraeGarden
These flowers are part of the Belladonna group, which is also a part of the larger buttercup family. As mentioned above, there are numerous hybrids, but D. elatum and D. grandiflora are the most popular varieties. Below are a few different cultivars of elatum and grandiflora that can add a source of beautiful cut flowers to your garden.
Delphinium grandiflora ‘Blue Butterfly’ grows 14 inches tall and has blue-purple flowers. More heat tolerant than other cultivars.
Delphinium elatum ‘King Arthur’ grows 5-6 feet tall and has reddish-purple flowers with white centers. This creamy white center is referred to as a white bee.
Delphinium elatum ‘Dasante Blue’ grows 3 feet tall with rich blue flowers with purple undertones.
Delphinium elatum ‘Pacific Giants’, as its name would suggest, grows to a gigantic 7 feet tall! Blooms are double flowers that range from light blue to pink, purple, and white.
Summer Stars (white)
Delphinium grandiflora ‘Summer Stars’ grows 14 inches tall with soft blue flowers.
Summer Morning (pink)
Delphinium grandiflora ‘Summer Morning’ is the first true pink variety of Chinese delphinium and grows 12-14 inches tall.
Dark Blue White Bees
The Delphinium cultorum ‘White Bees’ plant is not a grandiflora or elatum species, but it’s worth mentioning for what it brings to the garden. It has deep violet blooms with a stark white center dashed with black stamens. The plant is a semi-dwarf and reaches roughly 3 feet tall.
Delphinium Plant Care
You can see flower development well in this drooping delphinium. Source: Lexie Stevenson
Delphiniums have a few specific care requirements to be met. Once they are provided with their ideal growing conditions, then this perennial will reward with cut flowers from the garden for the next 2-3 years at least!
Sun and Temperature
Delphinium flowers require full sun exposure, at least 6-8 hours of full sun per day. In areas with hot and dry weather in the summer, this plant can benefit from light shade in the afternoon, during the hottest part of the day.
Delphiniums do best in USDA growing zones 3-7 as they appreciate not-too-hot and not-too-cold weather, and they prefer temperatures of 70-75 degrees Fahrenheit. The flower spikes are frost-tender and will die back in the winter garden. They can be cut back to the ground, and this perennial will come back in the spring.
Water and Humidity
The ideal time to water Delphiniums is in the morning or later in the afternoon after the day’s heat has passed. They require at least 1-2 inches of water per week. They are somewhat drought tolerant but do not tolerate prolonged periods without moisture, especially during intense heat where they are planted in full sun.
It’s best to water Delphinium plants at the base to help keep the foliage dry and avoid possible fungal issues. A soaker hose at the base of the plant or drip irrigation lines can help you achieve this easily. Once the flower stalks have died back, and the plant has gone to seed in the early autumn, then you may cease watering. Resume watering again in the spring when young plants appear.
Delphinium flowers put on their best show when they’re planted in well-drained soil. They prefer a light loamy mix of rich and fertile soil. Adding compost to your soil at the time of planting can help increase the drainage of poor or heavy soils. Delphiniums can survive in neutral soil but prefer slightly acidic soil with a pH range of 6.5-7.
Fertilizing Delphinium Plants
Staking the flower spikes will prevent drooping. Source: Paul Gulliver
As mentioned above, Delphiniums benefit from adding compost or other organic matter to help increase drainage, and that can act as a fertilizer for these heavy feeders. Yellowing foliage or stunted growth often indicates that the plant needs more fertilizer.
If you wish to give them an extra boost, then a 10-10-10 balanced liquid fertilizer can be added every 2 to 3 weeks throughout the flowering season. Fertilizing will help ensure that you get the most out of your blooms.
Pruning Delphinium Plants
Although it isn’t absolutely necessary many gardeners choose to prune their delphinium flowers in order to extend their bloom time. Thin shoots after the main flower spike has bloomed. This can be accomplished by cutting back the main stem to the side shoots to encourage them to bloom.
Since delphinium flowers have a columnar upright growing habit of tall flower spikes, they may also require staking at this stage. They can grow several feet tall and can easily be blown over in strong winds if not provided with some sort of support.
Delphinium Plant Propagation
Delphinium flowers will self-seed year after year as garden perennials. However, these seedlings are rarely true to type – meaning that the seeds may not produce a flower that is the same color or type as the parent plant.
Many popular Delphiniums are hybrid crosses which results in the instability of its offspring. If you’d like to have more control over which delphiniums pop up in your garden, starting them indoors from seed is your best bet.
Sow delphinium seeds 8-10 weeks before your last frost. These seeds take a while to germinate, anywhere from 21-28 days. For the highest germination results, a period of cold stratification is required. Place your seeds in your refrigerator for 2 weeks before planting.
Once all threat of frost has passed in the spring and nighttime temperatures are reliably in the 50s, you can transplant your delphinium flowers out in the garden. Dig a hole twice the diameter of the root ball and bury it at the same depth as its original pot. Keep well watering until your young plants are established.
Troubleshooting Delphinium Plants
Delphiniums come in many colors. Source: Paul Gulliver
Unfortunately, delphinium flowers can be fraught with pest and disease issues. Fortunately, there are very easy preventative measures to take that can keep your delphinium plants healthy and happy.
The most common issue with growing delphinium flowers occurs when the seeds haven’t gone through the proper cold stratification period. This is particularly important in warmer climates.
If you’re attempting a spring planting of delphinium seeds then be sure to store them in a refrigerator for at least 2 weeks before sowing. Otherwise, they will not germinate well. The most reliable method, however, is sowing seeds in autumn and allowing them to stratify naturally over the winter.
Cyclamen mites are semi-transparent and so small that they are invisible to the naked eye and therefore can only be identified until their damage is visible. They thrive in warm and humid environments and, for this reason, are commonly found in greenhouses. Their damage will cause new growth to appear drooping, twisted, or blistered with a wet appearance.
These mites can be killed by being immersed in water at a temperature of 110 degrees Fahrenheit. This should not kill the plants but will kill the mites. A good preventative measure is to keep the humidity levels low. For this reason, grow delphiniums in warm areas with dry weather.
Slugs and snails can also become an issue in humid and wet environments. Slug and snail damage will appear as large ragged holes in the foliage of your plant. You may even see a mucous trail near your delphinium plants. Slugs and snails are especially active in early spring before other insects have become active.
Choose a slug and snail bait that is made from iron phosphate and is safe to use around wildlife and pets. Snail traps can also be made by burying a cup or tin of beer at ground level. Snails and slugs are attracted to it, fall in, and then can’t climb back out.
Powdery mildew, southern blight, bacterial and fungal spots, mold, crown and root rot, white rot, rust, white smut, and leaf smut are all bacterial and fungal issues that are caused by or exacerbated by excess moisture and humidity.
Provide your plants with good air circulation and keep the area around your flowers free of plant material and debris to help prevent these issues. Most of the fungal issues can be treated with a copper fungicide though success varies, and it’s generally best to remove infected plant material before it can spread.
Frequently Asked Questions
Purple delphiniums. Source: Shelley & Dave
Q: Do delphinium come back every year?
A: Yes, delphinium plants are perennials and come back every year.
Q: Do delphiniums like sun or shade?
A: They prefer morning and early afternoon sun exposure, although in scorching areas, late afternoon shade is preferred.
Q: Are delphiniums poisonous to touch?
A: Yes, if the foliage or flower is touched, it can cause severe skin irritation.
Q: How long do delphinium plants last?
A: Most delphiniums bloom for 2-3 years.
Q: Should you deadhead delphinium?
A: Absolutely! This will encourage new growth and more blooms.
Q: Do you cut delphiniums down after flowering?
A: Yes, as perennials, they should be cut back to the ground after flowering.
Q: What month do delphiniums flower?
A: It blooms in early to mid-summer. If they are deadheaded after these first blooms are spent, then they can bloom again in late summer.
Q: Are delphiniums invasive?
A: No, these blooms are not considered invasive, as their tendency to self-seed isn’t coupled with high germination rates.