Blue Delphinium Care: All About Growing Tall Larkspur

Blue Delphiniums [Del-fin-ee-um] are perennial wildflowers of around 300 different species. All a part of the Buttercup family (which include Ranunculus and Clematis) and are native to the Northern Hemisphere.

Part of the family is a group of dwarf varieties referred to as the Belladonna group.

flowering Blue Delphinium

Its name ‘Delphinium’ has Greek origins and is derived from the Greek word for ‘dolphin’ since the flower bud was thought to resemble a dolphin’s nose.

You may also hear called by the name “larkspur.”

Overtime, tall delphinium hybrids were developed from the species Delphinium elatum.

Other species include:

  • Delphinium grandiflorum – called Chinese larkspur
  • Delphinium leucophaeum – endangered white larkspur
  • Delphinium Andersonii – known as Anderson’s larkspur

Blue Delphinium Care

Size & Growth

When delphiniums are cared for properly, some hybrids reach heights of 4′ – 6′ feet and require staking.

The larkspur is recommended for USDA hardiness zone 5a – 9b.

Flowering and Fragrance

The bright true blue flowers of the delphinium are known to attract hummingbirds and other pollinators along with adding some life to any garden.

Flower spikes begin in late spring. The bloom time is generally from early summer to mid-summer and may also re-bloom during the late summer or early fall.

Flower colors vary from common colors including blue, pink, white and purple.

Most plants are characterized by blue florets (or blue flowers), palm-shaped leaves with 3-7 lobes and strong stems. 

Flower spires may have different blue shades based on the species or hybrid. The perennial larkspur has dark blue flowers with an almost black center. 

Other shades include light blue flowers and sky blue flowers.

Light & Temperature

Delphiniums need to exposure to full sun to keep them from having a “leggy” look.

They may also bloom in areas of partial shade which receive at least 3 hours of sunlight.

Grow them outdoors after the last hard freeze, spring is an ideal time for planting them.

Watering and Feeding

Delphiniums bloom when they receive a good amount of water and fertilizer. 

The water shouldn’t, however, wet the leaves and flowers as this encourages mildew production. Watering with soaker hoses is a good option.

Soil & Transplanting

When planting delphinium, the soil type is very specific, it should be well-drained and damp.  

The soil should ideally be neutral, but slightly alkaline soil is also alright.

Within 2-3 weeks, seedlings will start to sprout. Transplant these into separate small pots once the first few leaves have grown.

Grooming and Maintenance

If you notice old or fading flowers, trim them until they are just about a foot above the foliage and then water.

Once new growth begins, cut the old-growth off, apply more fertilizer and provide the plants with water.  

How To Propagate Delphiniums

Plant cuttings are typically used to propagate delphiniums. 

  • Find shoots around 3″ inches long and with a knife, cut through their base tissue. 
  • Cut under a leaf joint and remove the lower leaves to expose the bare stem.
  • Dip each cutting in hormone rooting powder to encourage plant growth and prevent it from decaying. 
  • Without covering the stalks of the cuttings, push them around the edges of a pot containing compost or mulch (for different types, attach paper labels).
  • Cover the pot entirely with plastic for a few weeks or until the cuttings have started rooting.  
  • Once roots appear, remove the plastic and gently separate the cuttings taking care not to remove all the compost. 
  • Keep each cutting in a separate, large pot until they’re strong enough to be planted outside.

Delphinium Pest or Disease Problems

If the soil is too damp, diseases such as bacterial leaf spot or powdery mildew may attack your delphinium plants. 

Spraying sulfur is often the recommended action. 

In order to avoid such problems to begin with, keep the soil well-drained.

Another possible threat to your plants is crown rot where the stems start wilting. 

Plants affected by this need to be taken out and destroyed before they affect the rest of the crop.

Pests such as caterpillars, aphids, slugs, nematodes and beetles are also a threat to your plants. 

Is Delphinium Toxic or Poisonous?

The entire flower and plant are toxic for humans and ingesting it may lead to digestive issues and skin irritation. 

Larkspur has also been known to cause cattle poisoning and death in the United States.

Are Delphinium Plants Invasive?

Delphiniums are not invasive and in fact, may be planted in place of actually invasive plants such as purple loosestrife.

Suggested Uses For Delphinium

They make wonderful additions to a cutting garden and are deer resistant. They have long been a choice flower for the perennial border.

The juice of the flowers may be mixed with alum to create blue ink. 

However, the poisonous nature of the plants limits their usage.