How to Plant, Grow, and Care for Delphiniums

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 four feet tall, so be sure to place 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 one foot tall. 

However, they are toxic to the touch and livestock and pets if ingested. So be sure to grow delphiniums in an area inaccessible to pets and/or small children. Many different varieties and hybrids are available, all of which 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 known for their deep blue flowers but also come in a range of different colors. 

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Delphinium Plant Overview

Plant Type Annual or perennial Family Ranunculaceae Genus Delphinium Species Delphinium sp	Native Area Most of the world, except South America and parts of Africa Exposure Full sun Height 1-4’ Watering Requirements Moderate	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 Maintenance Low Soil Type Well-draining, fertile, rich Hardiness Zone 3-9

What is a 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. 

Native Area

Delphiniums, depending on their species, can be found worldwide. They are found on every continent except South America and are scarce in most of Africa. In the US, despite their toxic traits, delphinium flower stalks were used by Native Americans to make blue dye. In ancient times, they were used to repel scorpions, lice, and other parasites. 

Characteristics

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. Don’t plant delphiniums in an area not easily accessible to small children and/or pets. If ingested, it can lead to severe paralysis or death.

Varieties

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 that can add a source of beautiful cut flowers to your garden. 

• Delphinium grandiflora ‘Blue Butterfly’: this one grows 14 inches tall and has blue-purple flowers. It is more heat tolerant than other cultivars. 
• Delphinium elatum ‘King Arthur’: This variety grows five to six 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’: This variety grows three feet tall with rich blue flowers with purple undertones. 
• Delphinium elatum ‘Pacific Giants’: As its name would suggest, grows to a gigantic seven feet tall! Blooms are double flowers that range from light blue to pink, purple, and white. 
• Delphinium grandiflora ‘Summer Stars’: This soft blue flowering variety grows 14 inches tall. 
• Delphinium grandiflora ‘Summer Morning’: This is the first true pink variety of Chinese delphinium and grows 12-14 inches tall. 
• Delphinium cultorum ‘White Bees’: 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 three feet tall. 

How to Grow

Delphiniums have a few specific care requirements. Once they are provided with their ideal growing conditions, then this perennial will reward with cut flowers from the garden for the next tow to three years at least! 

Light

Delphinium flowers require full sun exposure, at least six to eight hours per day. In areas with hot and dry summer weather, they can benefit from light shade in the afternoon, during the hottest part of the day. 

Water

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 one to two 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 delphiniums at the base to help keep the foliage dry and avoid possible fungal issues. A soaker hose at the base or drip irrigation lines can help you achieve this easily. Once the flower stalks have died back and it has gone to seed in the early autumn, then cease watering. Resume watering again in the spring when young plants appear. 

Soil

Plant delphiniums in well-drained soil for the best show. 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. 

Temperature

Delphiniums do best in USDA growing zones 3-9. They appreciate not-too-hot and not-too-cold weather and prefer temperatures of 70-75°F (21-24°C) The flower spikes are frost-tender and will die back in the winter garden. Cut back to the ground, and this perennial will come back in the spring. 

Fertilizing

As mentioned above, delphiniums benefit from adding compost or other organic matter to help increase drainage, which can act as 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, add a balanced liquid fertilizer every two to three weeks throughout the flowering season. Fertilizing will help ensure that you get the most out of your blooms. 

Maintenance

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. Accomplish this 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.

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 their 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 eight to ten 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 two 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. 

Common Problems

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.  

Growing Problems

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 two 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. 

Pests

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°F (43°C). 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. 

Snail traps can be made by burying a cup or tin of beer at ground level. Snails and slugs are attracted to the cup or tin, fall in, and can’t climb back out. 

Diseases

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. It’s generally best to remove infected plant material before it can spread. Remove severely damaged plants before they infect healthy ones nearby.