How to Plant and Grow Delphiniums

Most commonly grown for its beautiful, tall spires of blue blooms, delphiniums have long been planted in perennial gardens. These elegant plants add a strong vertical element. Because some varieties can grow up to 7 feet tall, plant these at the back of a garden border. If blue isn’t your color, you can choose delphiniums in a few other colors, too!

Delphiniums are sought after and planted for their blue flowers. These beautiful blues come in a variety of shades and forms. Many feature a white center, which adds a bright contrast to the deep, rich blue. Most delphiniums are in the blue and purple range, but they can also be found in pinks and reds. There are some stunning coral-colored varieties and rare yellow ones. These plants have attractive foliage in a pleasing green, with palm-shaped leaves like a fern.

Delphinium plants and seeds are toxic.1 Plant them in a location away from children and pets.

Where to Plant Delphiniums

Delphiniums prefer cool summers and moist soil, so they don’t tend to do well in hot, dry weather. Plant delphiniums in well-draining soil in an area that receives 6 to 8 hours of sun daily. A location that provides some shelter from strong winds protects the tall flower stalks.

How and When to Plant Delphiniums

Spring and early autumn are the best times to plant delphiniums. They enjoy rich soil, so add compost to the planting holes. Position each plant so the top of the root ball is level with the soil surface. Space the plants 2-3 feet apart, depending on variety, and water them. Don’t let them dry out completely.

Delphinium Care Tips

Delphiniums are well-loved, but they can be fairly short-lived and picky when it comes to garden conditions.

Light

Delphiniums should be planted in full sun for the best blooms and sturdiest stems.

Soil and Water

Plant delphiniums in well-drained soil with plenty of organic matter. While it’s important to keep the plants consistently moist (they don’t handle drought well), be sure that the soil has proper drainage. Standing water can lead to crown rot, which causes the whole base of the plant to rot and will eventually lead to death.

Temperature and Humidity

One of the most important things to keep in mind is that delphiniums don’t like hot summers; they perform best in mild, humid weather. When it does get hot, the plants might die back to the ground. If you’re lucky, they may come back as it cools back down. In anything warmer than Zone 7, these plants are typically treated as annuals.

Fertilizer

Fertilize delphiniums in the spring when the plants begin to grow and again while they are flowering using a granular 10-10-10 fertilizer.

Pruning

Once the delphinium blooms are finished, deadhead them and remove the stalk to encourage a small second bloom.

Pests and Problems

In too much shade, especially in humid climates, fungus issues can arise on the foliage. Powdery mildew, botrytis, and leaf spot are all common problems that delphiniums struggle with. The best fungal control method is prevention, so make sure the plants are in well-ventilated areas and full sun to keep foliage dry. If your plant needs any supplemental watering, do it at the base so that the leaves stay dry.

Because these plants are tall, they often need staking or support from neighboring plants.

Delphiniums are known to attract slugs.

How to Propagate Delphinium

The best method for propagating delphiniums is to take a basal cutting in spring when the new shoots appear. Cut a small side shoot below the soil level, being careful to take some of the base. Dip the base in rooting hormone and pot it in a mixture of potting soil and sand or perlite.

Types of Delphinium

‘Blue Butterfly’ Delphinium

Delphinium grandiflorum ‘Blue Butterfly’ grows to only 14 inches tall and has deep blue flowers with a hint of purple. It tolerates heat better than other delphiniums, blooming through most of the summer. Zones 4-7

‘King Arthur’ Delphinium

Delphinium elatum ‘King Arthur’ is one of the Round Table Hybrids with 5- to 6-foot-tall flower spikes. It has reddish-purple flowers with a creamy white center called a bee. Zones 3-7

‘Dasante Blue’ Delphinium

Delphinium elatum ‘Dasante Blue’ is a compact selection with rich blue flowers with light purple tones. It grows 34 inches tall and 12 inches wide. Zones 4-7

Pacific Giants Series Delphinium

Delphinium elatum Pacific Giants Series are towering plants with bloom stalks reaching up to 7 feet tall. Colors range from light blue to white, pink, and purple. Zones 3-7

‘Summer Blues’ Delphinium

Delphinium grandiflorum ‘Summer Blues’ offers soft blue flowers in summer. It grows 14 inches tall. Zones 4-7

‘Summer Stars’ Delphinium

Delphinium grandiflorum ‘Summer Stars’ is a dwarf variety that produces pure-white flowers in summer. It grows 12-14 inches tall. Zones 4-7

‘Summer Morning’ Delphinium

Delphinium grandiflorum ‘Summer Morning’ is the first true pink variety of Chinese delphinium. It grows 12-14 inches tall, blooming all summer long on well-branched plants. Zones 4-7

Delphinium Companion Plants

Joe Pye Weed

Joe Pye weed is a showstopper of a prairie native, producing huge, puffy flower heads in late summer. It prefers moist soils, but with its extensive root system, it also tolerates drought well. It’s a large plant, growing 4 to 6 feet tall. Closely related, hardy ageratum is a spreading plant that grows to 2 feet tall. Another relative, white snakeroot, reaches 4 to 5 feet tall. All are great for naturalistic or cottage plantings and for attracting butterflies.

Salvias

There are hundreds of different types of salvias, commonly called sage. They all tend to share beautiful, tall flower spikes and attractive, often gray-green leaves. Countless sages (including the herb used in cooking) are available to decorate ornamental gardens, and new selections appear annually. They are valued for their very long blooming season, right up until frost. Not all are hardy in cold climates, but they are easy to grow as annuals. On square stems, clothed with often-aromatic leaves, sages carry dense or loose spires of tubular flowers in bright blues, violets, yellow, pinks, or reds that mix well with other perennials in beds and borders. Provide full sun or very light shade in well-drained average soil.