Another name for Delphinium is ‘Larkspur’. These beautiful blooms add a touch of grace to any garden and make a wonderful bouquet of cut flowers that will last about seven days in a vase. The modern delphinium is one of the most spectacular and popular of garden flowers. There are a wide ranges of colours, several flower forms, and varieties of different heights.
You can never have too many delphiniums. They are glorious plants with flower spikes that can grow up to 180cm tall. Normally, they are a range of blues, but are also available in white, pinks, and purple. They are standouts as background plants.
The delphinium is a genus of fully to half-hardy perennials, biennials and annuals so much admired particularly in the cottage garden setting. When grown in warm zones they are generally treated as annuals while in cool zones they can be successful as perennials. Delphiniums are tall, majestic plants with showy open flowers on branching spikes. Each flower has 5 petal-like sepals with 2 or 4 true petals in the centre called a bee.
Hybridisation of delphiniums has resulted in many new colours and attractive flower forms and growing heights. Flower colours range in shades of blue from palest sky, through to gentian and indigo; rich purple, lavender, pink to purest white.
The modern delphinium is the result of hybridisation of delphinium species from wide and varied parts of the world. Crosses made by growers keen to improve specimens they were able to acquire have resulted in the modern plants, which are truly spectacular. Many are varieties that are disease resistant, offering protection against both powdery mildew and black spot.
Some varieties of delphiniums may grow up to 180cm tall, making them excellent background plants. The Chinese delphinium (Delphinium grandiflorum) grows 60cm-90cm tall and therefore suited to the middle or front of the perennial border. Just like most other varieties, it will bloom throughout the summer if the plants are cut back regularly. The Belladonna delphinium (Delphinium x belladonna) is a cross between D. elatum and D. grandiflorum. These plants produce multiple flower stems that grow to 90cm-120cm. ‘Dwarf Pacific’ hybrids grow only 60cm tall. ‘Blue Butterfly’ is one of the shortest delphiniums maturing at 34cm.
Delphiniums give their best performance in well-drained soils in full sun but they can be grown in dappled or part shade. Delphiniums do not like wind. They do like a lot of water in the summer. Be sure to plant in the spring. They can be grown in most soils with good drainage as long as it is fertile and nutrient-rich. They are heavy feeders and therefore require extra nutrients particularly in early spring and later in the season. Mulching with manure at the start of the season and a liquid feed every two to three weeks throughout the summer will giving them a rich diet for the development of their flowers. Stunted growth and yellow foliage are signs the plants need additional fertiliser.
Dig a hole twice the size of the plant pot and work in some bone meal. Place the plant in the hole so the foliage is at ground level and recover with soil, making sure the plant is positioned firmly. Water immediately and then daily until the plant has settled in. Delphiniums should never be dry. Mulching may help retain water. Depending on the variety, place delphiniums 30-90cm apart.
Tall varieties benefit from being staked. Place stakes early in season to prevent damaging roots. Windbreaks like hedges or open fencing will help support them in strong winds. Shorter varieties usually have sturdier stocks and are less likely to topple.
Thinning delphiniums annually is a must or the plant will exhaust itself blooming. Cut all foliage and stems to ground level in autumn.
An old time tip to extend their bloom time is to remove seed pods as they develop and work wood ash into the soil around them.
The life expectancy of many perennial delphiniums is often only two or three years, but occasionally they can last much longer.
GROWING FROM SEED
Good seed is necessary to produce good plants. Purchase the best hand pollinated seed that is obtainable. Order seeds of newer hybrids and follow the instructions of the hybridiser in getting your plants started and out into the garden early. Use a good, loose potting soil, firming it down into flats or pots with a wooden block and then moisten before sowing the seed. Cover seeds by sifting soil over them leaving a layer of about 1mm. Keep moist and shaded until seeds germinate, then remove the shade.
PESTS AND DISEASES
Unfortunately, some delphiniums can be susceptible to powdery mildew. Some gardeners use the same fungicides as for their roses with good result. Other gardeners swear by maintaining soil health through composting and mulching. Also, combat slugs by hand picking and destroying, or using slug bait, especially in spring when plants are just coming up. You could also try sprinkling with cayenne pepper or cayenne pepper tea after every rainfall to deter them.