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Delphinium Care

Last Updated on September 16, 2022 by Plant Mom Care

Delphinium, a perennial genus of around 300 species of flowering plants from the Ranunculaceae family, is widespread in the Northern Hemisphere as well as the tropical mountains of Africa. The “larkspur” common name of the species is also shared with species from the Consolida genus. 

The deeply lobed leaves have three to seven serrated, pointed lobes. The flowering stem grows up straight and greatly varies in size between the various species, from 4 inches high in some high-altitude species, up to 6 feet tall in the large meadowland species.

These plants usually bloom in summer in clusters of flowers of various colors such as purple, blue, red, yellow, and white. The flowers of most species have 5 sepals which grow to form a spur at the tip, giving the plant its common name. Inside the sepals are 4 small true petals and usually of the same color as the sepals and are pollinated by bumblebees and butterflies. The seeds are small and usually shiny black. 

Gardeners since Victorian times have grown this plant species in cottage and flower gardens. Most of the hybrid cultivars that have been developed originate from D. elatum. Victor Lemoine, a Frenchman first started developing hybrids from this species in the 19th century. Since then, breeding continued into the 20th century by cultivators in the United States, New Zealand, and Japan. Several cultivars ranging in shades of pink, white, blue, and purple are grown as garden plants and for the cut flowers industry and are often used in displays and competitions at the garden and flower shows.

Unfortunately, many gardeners consider the species as difficult to cultivate and avoid growing it in their gardens however, this attractive plant produces some of the best flowers in summer and its lovely blooms are worth some effort. 


Delphinium Light Requirements

These plants grow best in sunny areas, for the best growth select a spot that gives the plants a good exposure to morning sun and some afternoon shade, particularly in hot climates. They should get about 6 hours of sunlight every day.


Delphinium Watering

They prefer their soil to be constantly moist dry conditions will make the plants wilt or die. Mulching will help retain moisture, keep the roots cool and prevent the soil from drying out on warmer days. This also helps to prolong their flowering phase in summer.


Delphinium Humidity

These plants prefer low humidity conditions. These plants might live for only 2 or 3 years in hot and humid climates.


Delphinium Temperature 

These plants prefer cool to reasonably warm summer weather between 70-75°F. It grows better in places where heat waves are not normally experienced. It is suggested that you force these plants to flower with temperatures of 60 and 70°F – plants growing at 70°F will take about six weeks to start flowering, while plants growing at 60°F will start flowering in 10 weeks. 


Delphinium Soil

Well-draining, rich, and slightly alkaline soil is preferred while mulch will help retain moisture, it shouldn’t be applied close to the stems it will make them rot. These plants are rather finicky when it comes to soil quality and this is important to successfully cultivate them. 


Delphinium Repotting

Growing these plants in containers is easy provided the container is large and wide to comfortably contain the shallow and wide root system. Place a few small chunks of rock over the drainage holes to improve drainage and add a layer of rich compost. 

Laying the container on its side will make it easy to slide the plant out without damaging the roots, loosen any matted or tangled roots before transferring the plant to the new container with the root system sitting below the rim. Fill the container with rich soil amended with perlite or coarse sand to improve drainage. Water it well, perhaps adding more soil as it settles. 


Delphinium Propagation

These plants are usually propagated from seeds, cuttings, and dividing the roots. Remember, never take seeds or cuttings from an unhealthy plant.

Propagation by Seeds:

This can be a rather challenging process. First, let a few flowers remain on the plant to produce seed pods that turn dark brown when mature, remove and open the pods to harvest the seeds and store them in a dry location until you’re prepared to plant them.

The seeds have to be cold stratified before sowing. Place the seeds in your refrigerator for a week, seeds purchased commercially have already undergone this process before being packed and sold. Sow the seeds in pots or trays using a suitable starter soil mix about 8 weeks before the last frost forecast. Once they develop at least 2 pairs of leaves, take them outdoors and back inside at night to harden them for around a week before you transplant them into their permanent location.

You can also plant the seeds in your garden in early summer. They are heavy feeders and enriching the soil with compost gives the seedlings a nice boost. Prepare the selected spot by loosening the soil with a spade or garden to about 12 or 15 inches deep, this will help the roots spread and set easier.

Put the seeds on a damp coffee filter and fold them in half, placing them where they won’t be disturbed for around a week. After they germinate, plant them in the prepared location with good spacing in between and cover them with a layer of soil. Water the soil to keep it dampened and monitor the temperature (which should be between 70-75°F). Seedlings will start emerging in 3 weeks.

Propagation by Basal Cuttings:

This is probably the simplest way to propagate these plants. Basal cuttings are preferably taken in spring when new shoots appear, cut a shoot just under the soil surface, taking not more than two cuttings a single plant. Remove all the foliage, keeping just a few leaves. 

Plant them in prepared containers filled with a mix of perlite and compost. Water and keep the pots in an undisturbed sunny spot. Keep the soil dampened, misting the leaves to stop them from becoming dry, roots should develop within a few weeks. Once the roots are set, continue watering as normal, harden them before moving them to their permanent spot.

Propagation by Division:

Mature plants can be divided from 3 to 4 years, this should be done in spring when new growth is emerging. This also helps rejuvenate established plants. Water the plants well 24 hours before dividing this helps to hydrate the roots to survive this process.

Cut off around 1/3 of the plant’s foliage makes it easy to handle the plants. Dig a circle of 7 or 8 inches around the plant to protect the roots from accidental damage. Dig at an angle to help you easily lift the plant from the soil. If it is growing in a pot, simply ease it from the pot.

Remove any soil and examine the roots. The roots are easily separated by pulling them apart. Divide the root clump into 4 portions, with each portion having healthy roots and foliage. Replant the sections into prepared pots or in your garden.

Additional Care

In spring, after new growth begins to appear, feed the plants regularly with a balanced 10-10-10 fertilizer for a long-lasting flowering season. The plants need regular fertilizing until the flowering season is over. Generally, these plants need feeding once every 2 weeks, signs that the plants need fertilizing show up in stunted growth or yellow foliage. 

Deadhead blooms when they fade in summer this helps more flowers to develop and also prolongs the flowering season. When the flowering season ends, cut away the flower stalks.

Thin out growing shoots when they become 3 inches high this encourage the formation of healthy flower spikes to form. Leave 2 or 3 shots on younger plants and 5 or 7 shots on mature plants.

Most varieties are tall and need staking, particularly if they grow in windy areas. The stems of these plants are hollow and easily break when stressed by wind. 

Delphiniums Common Problems

Over-watering the plants often leads to the development of root rot. Cyclamen mites can plague the plants, including powdery mildew if the leaves are wet or when the plants are not spaced out properly.

Rust makes rust-colored spots appear on leaves, removing affected leaves and any plant debris in the soil to stop the problem from recurring.

A bacterial infection called delphinium black blotch causes large black splotches on leaves. It particularly happens in wet summer, remove any infected plants to stop the infection from spreading to other plants in your garden.

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