Sweet Pea Specialists
Delphiniums - everything you need to know about how to grow them and how to condition their flowers.
Updated: Jul 22, 2022
Delphinium (Delphinium grandiflorum) is a genus of about 300 species of annuals, biennials or perennials in the family Ranunculaceae. They are a favourite of cottage gardens. Their tall flowers are ideal for creating presence towards the back of garden beds or near fence lines. Plus they can also be grown in pots. Delphiniums come in two sizes dwarf (30cm) or tall (1.8m) in the colours of blues, lavender, pinks and white.
Delphinium elatum Magic Fountain 'Blue',
Campanula persicifolia and Campanula portenschlagiana.
These are easy plants to grow given the right conditions. They prefer a neutral to slightly alkaline soil located in full sun to part shade. Gentle morning sun is preferable for delphinium plants, which are picky about extreme differences in temperatures. Provide afternoon shade, especially when planted in hotter zones. Grow delphiniums in an area protected from winds. Prepare soils beforehand by working through well broken down animal manure and organic matter. Delphiniums will require additional watering during summer. Do not let these plants dry out. Keep these plants moist but not wet. Mulch to keep soil moist and cool. Mulch will also protect the plants during winter. Plants will need to be protected from late frosts as the new shoots can be damaged. The taller varieties may require staking, it is best to place the stake at the time of planting. Plants will spread but this will happen slowly.
Protect plants from snails and slugs.
Delphiniums flower in summer with a second flush in autumn. The flowers are a favourite with florists and be dried. Flowers can last up to 10 days as the buds continue to open. Condition flowers overnight in cold water. Allow plenty of room for flowers to open and stems to stretch. Florets bruise easily and break off if tangled.
Flower stems can be dried by hanging them upside down.
I have found growing delphinium from seed to be very easy. I simply potted up the seeds and left the pots outside ensuring during the warmers months that they were well watered. Since I used fresh seeds, germination was high.
However, following are some tips:
For the highest germination rate delphinium seeds must be fresh and come from disease free stock. Our seeds are harvested and stored in the refrigerator until they are posted. We also replace our seeds every season.
Links to purchase seeds:
Use a disease free seed sowing mix to avoid “damping off” to which delphiniums are susceptible.
Seeds only need to be lightly covered. Place pots in an airy place with gentle light.
Water pots only enough to keep the surface from drying out. It is very important not to overwater or the seed and/or seedlings will quickly rot.
Germination occurs around 18 to 24C. Do not allow temperatures to exceed 26°C.
Pot seedlings up when they have around three sets of true leaves. Keep the seedlings in these pots until they around 10cm and plant out after the last frost.
Link to Purchase Tube Stock Plants
All members of the genus Delphinium are toxic to humans and livestock.
Delphinium formosum is a many-stemmed perennial growing to 60-180 cm. The flowers are around 4cm and are deep violet-blue.
I have this plant growing at the Tasmanian farm.