How To Grow Delphiniums

Grown for the flowers Delphinium plants are an erect perennial, from low growing ‘dwarf’ cultivars at around 20cm through to to 2m tall plants depending on species.

Quick Facts

• Botanical name: Delphinium species and hybrids
• Plant type: Herbaceous perennial
• Height: 20cm to 2m depending on variety
• Position: Full sun to part shade
• Soil: Humus-rich, moist, well-drained soil
• Flowering season: Spring to summer
• Flower colours: Blue, purple, pink, white and red
• Climate: Best in cool to temperate climates

Quick Growing Guide

• Grow in cool climates – Delphiniums thrive in cool weather and struggle in prolonged heat and humidity.
• Plant in rich, well-draining soil – Add compost and keep soil consistently moist, but never soggy.
• Provide full sun wisely – Full sun in cool areas; morning sun and afternoon shade in hot climates.
• Support tall flower spikes – Stake or tie plants to prevent flopping or snapping in wind and rain.
• Expect a short lifespan – Most live 2–4 years; propagate by division, cuttings, or seed to keep them going.
• Feed regularly – Use compost and a balanced fertilizer in spring and again after the first bloom.
• Protect from slugs – Guard young shoots with barriers or organic slug controls before damage occurs.
• Deadhead for repeat blooms – Cut spent flower spikes back to new shoots to encourage a second flush of flowers.

Dephiniums in warm climates

In warm climates, success comes from avoiding heat rather than trying to make delphiniums tolerate it. Early planting, afternoon shade, cool roots, consistent moisture, and selecting more heat-tolerant varieties can make a significant difference.

Heat Tolerant Varieties

• Pacific Giants – originally developed in California and generally more tolerant of warm conditions.
• Guardian Series – known for better heat performance and first-year flowering.
• Aurora Series – another option that handles warmer summers reasonably well.
• Delphinium grandiflorum (Chinese delphinium) – naturally shorter but generally more tolerant of heat than D. elatum.
• Mediterranean species like Delphinium requienii are also better suited for hotter regions.

How To Grow Delphiniums – Basic Care

Delphinium plants like a moist humus rich soil and as with all soil preparation this is best done a few weeks before planting. Weed the area well and dig in some well rotted compost and cow manure, add a handful of blood and bone and dig over again. Leave for a few weeks and then you are ready to plant.

Usually grown from seedlings or seeds, and are best planted out in early autumn, seeds can be sown in a cold frame to get a head start. Established plants can be divided as clumps expand, this is best done in late winter to early spring. Check the variety as some are taller growing than others and may be best planted further back in the border.

The varieties grown most widely found for sale for the home garden are the taller growing varieties, these delphiniums require full sun with some shade from the hot afternoon sun, a moist humus rich soil and delphiniums may require staking.

lower colours range from white and blue through to pink, deep rose, purple and even near-red shades. Used widely in cottage garden borders we include Dowdeswell’s delphiniums from Tesselaar Bulbs.

Climate Requirements

Delphiniums perform best in cool to temperate climates where summers are not excessively hot or humid. In warmer regions they benefit from morning sun and protection from hot afternoon sun. Good air circulation helps reduce fungal problems during humid weather.

How To Plant Delphiniums

Delphiniums grow best in full sun in cooler climates. In warmer regions they benefit from morning sun and protection from the hottest afternoon sun.

1. Prepare the soil before planting. We dig in some well rotted compost, aged cow manure and some blood and bone (bone meal).
2. Delphiniums are hungry plants and benefit from regular feeding throughout the growing season.
3. A well drained soil is essential, so raise up the garden bed in damp soils.
4. Spacing and Support
   How far apart to plant Delphiniums is debatable. The closer they are are together, the taller they grow. Taller plants can be a little weak and fall over, however if you stake them they will survive.
   We plant them at around 70 cm apart and stake them with bamboo canes. Some growers plant them so that they grow through a wire mesh for support. We find the stakes are easier.

After Planting

• Mulch around the plants to maintain a cool root run.
• After flowering, remove the spent flower head to just above the ground level.
• In winter cut them back to the ground.
• In spring as new growth appears, fertilise and water as required.
• Fertilizer, Pests and Support

Fertilize with with a liquid seaweed fertilise as well a ‘worm castings tea’ every two weeks. Plants can be cut back after flowering to encourage a second flush, although some growers think that this decreases flower vigor the next year. Taller growing cultivars may require plant supports. The main pests are snails and slugs especially with the small seedlings.

Growing Delphiniums From Seed

Fresh seed generally gives the best germination results. Sow seed in trays filled with a quality seed-raising mix and keep moist but not wet. Germination usually occurs within 14–21 days in cool conditions. Seedlings can be transplanted once they have developed several true leaves.

Growing Delphiniums From Seed Video

Learn how to sow delphinium seeds and raise healthy seedlings in our step-by-step video guide by JohnnyA

Top Tips

1. Flowering from spring through to summer, the actual flowering period will depend on the climate zone. 
   
2. When the flower spikes begin to appear it time to fertilise with a liquid organic fertiliser and to keep the plants well watered. Mulch around the base of the plant will provide the cool moist rot run that they love.
   
3. Delphiniums are a perennial so they will die back over winter and reappear in spring as the weather warms. 
   
4. Grown for the attractive flowers the appear on tall spikes flower colour varies from white through to red, purple and the trademark blue. Green flowering types are also available.
   
5. Plant them where the receive around 7 hours of sun, morning sun is best in hotter climates, when the flowers on the first spike fade, you can prune back the flower spike down to where the smaller suckers or side shoots appear. These will prove a second flush of flowers, smaller spike, but still very attractive flowers.

Common Problems

Delphiniums can occasionally suffer from powdery mildew, crown rot and fungal leaf diseases, particularly in humid conditions or poorly drained soils. Good air circulation, regular watering at soil level and removing old foliage can help prevent problems.

Delphiniums v Larkspur

Delphiniums and ‘Larkspur’ are often confused, they are related, however ‘Larkspur’ are actually Consolida species. Delphiniums are perennials, Consolida are annuals.

Where To Buy Delphiniums

You can purchase delphinium plants and seed from specialist perennial nurseries, mail-order bulb suppliers and local garden centres. Look for named cultivars and modern hybrids that are better suited to most growing conditions.

TESSELAAR BULBS - Phone: 1300 428 527
357 Monbulk Road SILVAN VIC 3795
Guaranteed "garden worthy" bulbs, plants and perennials. Visit the website to browse our large range of daffodils or request the latest free catalogue.
www.tesselaar.net.au

GARDEN EXPRESS - phone :1300 606 242
470 Monbulk-Silvan Road Monbulk VIC 3793
"Guaranteed mail order flowering bulbs, perennials, roses, trees, landscaping plants, garden accessories and community fundraising Austra lia-wide."
www.gardenexpress.com.au

NUTSHELL PERENNIAL NURSERY and PLANT FARM
'Umbango' 750 Humula Rd, Humula NSW 2652
Phone 0408692773 Great Range of Perennial plants available for sale by mail order.
www.nutshellnursery.com.au

LYNN'S RARE PLANTS
PO Box 7040 Leura NSW 2780
Rare woodland plants, Trilliums Epimediums, Arisaemas, plus much more.www.lynnsrareplants.com.au

 

The best time to divide delphiniums is early spring, just as new growth begins to emerge. This timing minimizes transplant shock and gives the divisions a full growing season to establish. Avoid dividing in late summer or fall, as this can stress the plant before winter dormancy.

Divisions should contain several healthy shoots and a good section of roots. Replant immediately and water well until established.

Why You Should Divide Delphiniums

• Rejuvenates older plants
• Improves air circulation and reduces disease risk
• Encourages stronger, more abundant flower spikes
• Expands your garden with healthy new plants

Frequently Asked Questions

Do delphiniums come back every year?
Yes. Delphiniums are herbaceous perennials that die back in winter and re-emerge in spring.

Do delphiniums need staking?
Most tall-growing varieties benefit from staking, especially in windy gardens.

Can delphiniums grow in pots?
Dwarf varieties can be grown successfully in large containers filled with a quality potting mix.

When do delphiniums flower?
Most varieties flower from late spring into summer, with a second flush sometimes possible after deadheading.