Delphiniums: all about planting, caring for & propagating larkspur

Larkspur (Delphinium) is an absolute classic in the garden. Here you will learn everything you need to know about buying, planting and care of this beloved plant.

Larkspur (Delphinium) enriches any garden with its wonderful colours and its botanical name already suggests that its flowers resemble a dolphin. These tall-growing ornamental plants are a fixture in many gardens – we explain what else you should know about these beautiful plants.

Delphiniums belong to the buttercup family (Ranunculaceae) and are some of the most famous and certainly the most beautiful perennials that we can put in our gardens. But what perhaps not everyone knows is that larkspur is a poisonous plant, because the alkaloids it contains (elatin, delphinin and others) make the plants and their seeds extremely toxic.

Delphiniums: origin and characteristics

The various larkspur species originate either from the Mediterranean region or from Asia. The plant has upright stems, which are sometimes branched. These stems host wonderful single or double flowers – making them an eye-catching addition to your garden. Larkspur is also popular as a cut flower and for drying, due to its wonderful flowers. Delphiniums come in white, pink, red, blue and purple. These flower colours, of course, come in a wide variety of shades and the flowers can be seen from June to August.

Delphiniums can vary greatly in size, since the smallest species reach a height of only about 20 centimetres. Some varieties, however, manage to grow to a height of a whole two metres. This ornamental plant, of course, looks great in the garden, but also requires additional maintenance – as the tall plants are always at risk of tipping over, especially in strong winds. You also need to pay attention to larkspur’s neighbours, especially when planted in beds, since not every plant is suitable. Suitable neighbours for delphiniums are milky bellflower (Campanula lactiflora), irises (Iris barbata), shasta daisies (Chrysanthemum maximum), cranesbill (Geranium) or yarrow (Achillea filipendulina). Irises are even said to enhance the growth of larkspur. On the other hand, avoid placing phlox (Phlox) and asters (Aster) near delphiniums, as the roots of these plants do not like each other and can cause damage underground.

Larkspur species

There are many different types of larkspur, which differ in size, colour and their area of origin. In total, there are an estimated 400 different larkspur species, most of which originate from different parts of Europe. Larkspurs can be categorised botanically or according to the types of crosses or hybrid varieties.

Larkspur: botanical distinction

• Giant larkspur or hyacinth larkspur (Consolida ajacis)
• Branching larkspur (Consolida regalis)
• Siberian larkspur (Delphinium grandiflorum)

As you can already see from the different species names the systematics in the genus of delphiniums is very complicated and some of the species names have also changed in recent years. Such variations come about through more precise methods of analysis, since molecular biology now allows us to examine relationships between different plants more precisely than in the past, where the appearance of the plants alone determined the classification.

In breeding circles, the following species or hybrids are distinguished:

• Elatum group (garden larkspur)
• Pacific group (Pacific garden larkspur)
• Belladonna group (half-high larkspur)

Wild delphiniums are usually only annual or biennial, whereas cultivated garden forms are often more durable. Generally, the taller a larkspur, the longer it lives. For example, Pacific varieties live only up to three years, Belladonna varieties can live up to five years, and Elatum varieties can even reach the age of ten years.

Planting delphiniums

Larkspurs need a lot of nutrients, so you need to move them every now and then so that the soil does not become too depleted. Below are some points to consider when planting delphiniums, so that you can enjoy the beautiful ornamental plants for a long time.

The perfect location

For delphiniums to grow optimally, they need a sunny spot in your garden where they are protected from the wind. However, larkspur does not like to be in full sun, because it prefers sun overhead but shade below. It is therefore advisable to place other low-growing ornamental plants around the flowers that can provide shade. Delphiniums prefer loamy-humic soil, which is rich in nutrients but poor in nitrogen. For a larkspur seed to germinate, it requires a cool soil temperature of 10 to 12 °C.

Planting delphiniums: step-by-step

Delphiniums can be sown outdoors either as early as mid-October or in the spring in March and April. You can also sow larkspurs in containers and pots indoors from the end of March to grow them in advance. This can give the plants a head start in growth and protect them from pests and diseases when they emerge. In addition, delphiniums grown in this way are also protected from frost, as they are only planted out from mid-May onward. You should maintain a planting distance of 15-30 centimetres.

How to plant larkspur outside?

• Water the root ball of larkspur before planting
• Dig a hole that has enough space for the root ball
• Add fertiliser such as manure or compost to the planting hole
• Put the plant in the hole
• Make sure that the root ball is level with the ground
• Fill the hole with the excavated soil
• Press the earth around the plant firmly
• Thoroughly water the plant

Delphinium plant care

In order to enjoy your larkspur all summer long, you should pay attention to some things when caring for these plants. Thanks to their height, delphiniums are very susceptible to wind, so you should always look for a sheltered place for your larkspur, otherwise there is a danger that it will be knocked or blown over. Optimal care also includes pruning delphiniums in summer. As soon as the plants have flowered, you should trim the stems to 20 centimetres. The plant will be rejuvenated and can flower again. Thus, in late summer you can encourage a second flowering. Pruning is also recommended to prevent the delphiniums from growing too tall, because the higher the stems, the more susceptible they become to wind. Do not prune more than 20 centimetres, because it may no longer sprout again.

Watering larkspur

Delphiniums need sufficient and regular watering for optimal development, as they have a very high water requirement. If the weather is very hot and there are periods of severe drought, you should water the larkspur at least once a day, if not twice. To prevent heavy water evaporation, you can spread a layer of mulch around the larkspur or create shade with ground-covering plants.

Fertilising

It is highly recommended to add some fertiliser such as compost to the soil even before planting or sowing. Rotted horse manure is also particularly suitable for fertilising delphiniums. Since the plants are shallow rooted, you only need to apply fertiliser about 40 centimetres into the soil. It is recommended to fertilise perennial larkspurs organically twice a year, and it is ideal to fertilise once in the spring before budbreak and once in autumn after pruning. You can use our Plantura Flower Food to provide your delphiniums with enough nutrients to keep them protected through the winter.

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Composts, manures and other organic fertilisers should always be carefully worked into the soil, but care should be taken not to damage the roots of the plants. The advantage of organic fertilisation in autumn is that the fertiliser can already decompose somewhat, is broken down and thus guarantees your plants a strong start next spring. Should you use mineral fertilisers for your larkspur, it is recommended to always pay attention to the application instructions and especially to the dosage.

Propagating delphiniums

Larkspur will sow itself, if you allow the fruit clusters to fully ripen. If you are not satisfied with the self-sowing, you can also use another method. Delphiniums are normally propagated by dividing the cane.

What’s the best way to divide larkspur for propagation?

• Dig up your delphinium plant
• Divide the root ball with a spade
• Place the divided root balls in a bucket full of water
• Dig a planting hole and loosen the soil in it
• Mix compost into the hole in the ground
• Put the larkspur in the planting hole as previously described

Divide delphiniums in the spring, the best time for this is the month of April. In the best-case scenario, these delphiniums will bloom in the same autumn or in the next spring and delight our eyes with their wonderful blooms. Of course, you can also propagate larkspur by its seeds, which you can easily sow again. To do this, do not cut the plant back, you need to let it wither, so that the seeds can form. It is important not to cut back delphiniums after the first flowering, so that the seeds have enough time to mature. Fruits are then formed, which then contain characteristic triangular seeds. You can collect these fruits once they have turned brown and are dry – however, you must collect them before the fruits burst open on their own and self-seed.

If necessary, you should dry the collected fruit. Then clean the seeds and store them in a dry and dark place. In the spring, you can then plant the seeds indoors from March onwards or directly in the ground from May. If you propagate hybrid delphiniums yourself, the following generations will have different characteristics and their appearance will be different from the parent plants – but with this you can add some diversity to your garden.

Overwintering delphiniums

Delphiniums do not require special winter protection in open ground, except being cut back in autumn and an additional layer of compost. For perennial larkspurs this is enough to help them to sprout again in the spring. For annual and biennial varieties, you should either let them self-seed or collect the seeds.

However, plants that are cultivated in pots need shelter to get through the winter. These are more sensitive and should be protected from frost as follows:

• Wrap the pots with fleece
• Put the pots in a protected place, for example against a house wall or in corners
• Place the pots on styrofoam or wood to keep them off the cold ground
• Cover the plants with brushwood or leaves

Common diseases and pests

Delphiniums are also repeatedly threatened by several animal pests. They is particularly often infested by snails (Gastropoda), leaf miner flies (Agromyzidae), and broad mite (Tarsonemidae). However, some diseases also occur on larkspur, such as black blotch (Pseudomonas delphinii), powdery mildew (Erysiphaceae), or viruses. The occurrence of pests and diseases is often promoted by an unsuitable location – in the case of delphiniums, this is often too shady. You can use plant broths to strengthen larkspurs as a preventative measure. If the plant is attacked by fungi such as powdery mildew, then you can simply cut off the affected shoots and thus contain the infestation.