With their towering spires and jewel-toned blooms, delphiniums are the crowned royalty of the flower border. These perennial stunners may look high-maintenance, but with a few insider tips, you can grow them like a pro!
I’ve been growing delphiniums for over 30 years, and they still take my breath away every summer. From the first sprout in spring to the final bloom before fall, these flowers bring a sense of wonder and joy to my garden that never gets old. Whether you’re a seasoned grower or just planting your first spike, I’m excited to share what I’ve learned along the way.
1. Choose the Right Delphinium Variety
Not all delphiniums are created equal. Pacific Giants are tall, vibrant, and classic—but they’ll need staking to stand tall in the breeze. Magic Fountains offer the same beauty at a more manageable height of 3 to 4 feet, making them a favorite for gardeners who prefer a lower-maintenance option. New Zealand hybrids bring strong stems, dreamy double blooms, and vivid colors that truly stand out in the garden. If you’re gardening in warmer zones, opt for heat-tolerant types like Delphinium chinensis ‘Butterfly’ or the reseeding Delphinium consolida ‘Giant Imperial’.
If you’re short on time or prefer lower-maintenance flowers, go with the more compact varieties. Shorter delphiniums are not only less likely to flop, but they also adapt better to a wider range of garden conditions. Pay attention to your climate zone, and choose varieties that are known to thrive there for the best success. Starting with the right type makes everything else easier down the line.
2. Pick the Perfect Planting Spot
Delphiniums love sunlight, but they’re not fans of scorching heat. Choose a spot that receives at least six hours of morning sun and some protection from intense afternoon rays. Good air circulation is a must to keep mildew and blight at bay, so avoid overcrowding them. Shelter them from strong winds with a fence or windbreak, or be ready to stake taller varieties for extra support.
Even in cooler climates, it’s wise to avoid planting delphiniums in heat traps like against brick walls or south-facing slopes. Look for areas with gentle airflow, such as open beds or borders with ample space. Grouping them with other tall perennials that offer a little afternoon shade can also help buffer heat and wind. Location really is everything when it comes to growing thriving delphiniums.
3. Prep the Soil Like a Pro
Delphiniums thrive in fertile, well-drained soil with a slightly alkaline pH. If your garden soil is heavy clay like mine, enrich it with compost or aged manure and consider raised beds for improved drainage. Rich, airy soil supports deep root development and helps these hungry plants grow strong and tall.
Adding organic matter isn’t just about nutrients—it improves the soil structure, too. Sandy soils can benefit from added compost to help retain moisture, while clay soils need it to boost drainage. A yearly top-up of compost or well-rotted manure goes a long way in keeping delphiniums happy. Before planting, test your soil’s pH and aim for a range of 6.5 to 7.5.
4. Plant with Care
Plant delphiniums in early spring when the soil has warmed up. Dig holes twice the size of the root balls and plant them at the same depth as their containers. Space each plant 2 to 3 feet apart to allow plenty of room for growth and airflow. Give them a deep watering after planting, and keep an eye on them daily until they’re well established.
For fall planting, make sure to allow at least six weeks before your first frost so roots can settle in. Avoid planting too deep, as this can cause crown rot. Adding a thin layer of mulch right after planting helps lock in moisture and moderate soil temperature. Just keep the mulch a few inches away from the base of the plant to prevent rot.
5. Water and Feed Wisely
Delphiniums need consistent moisture, especially during dry spells. Water at the base to keep the foliage dry and disease-free. If your soil is already nutrient-rich, you might not need fertilizer, but if in doubt, apply a balanced, slow-release formula in early spring. Avoid excessive nitrogen, which leads to lush leaves but fewer blooms and weaker stems.
During especially hot weather, increase watering to prevent stress and wilting. A layer of mulch can help retain soil moisture between waterings. If you’re using liquid fertilizer, dilute it to half-strength to avoid burning the roots. Feeding lightly but regularly is better than overdoing it all at once.
6. Provide Support for Tall Growth
Look at the above photo closely. Notice the bent stem? That’s what happens if you don’t stake your delphinium. At least it kept blooming! Staking tall delphiniums is a must if you want them to stay upright and proud. Use bamboo stakes and soft twine, and place the supports early in the season before the plants get too tall. Position stakes in a circle around each plant and loosely tie the stems, leaving room for natural movement. Adjust ties as needed through the season, and consider leaving stakes in place until fall if your area is prone to windy weather.
You can also use metal plant rings or grow-through supports to keep things neat and tidy. The key is to be proactive—once the flower spikes start to bend, it’s harder to train them upright. Regularly inspect your support system, especially after storms or heavy rain. A well-supported delphinium is not only healthier but also more visually striking in the garden.
7. Keep an Eye Out for Pests and Diseases
Healthy delphiniums need vigilant care. Watch for aphids, slugs, and spider mites—common pests that can be managed with insecticidal soap, neem oil, or natural predators like ladybugs. Keep plants hydrated to deter spider mites, and hose them off occasionally to remove pests from the leaves. Prevent fungal diseases like powdery mildew and root rot by spacing plants properly, watering at the base, and applying sulfur or neem oil as needed during humid spells.
In damp conditions, Botrytis blight and crown rot can become a real problem. Remove infected plant parts immediately and avoid overhead watering. Slug damage can be reduced by keeping the area tidy and using barriers like copper tape or crushed eggshells. Staying ahead of pest and disease issues will keep your delphiniums lush and blooming all season long.
8. Prune for More Blooms
Pruning delphiniums encourages bushier growth and repeat blooming. After the first flush of flowers, cut the spikes back to a set of leaves to promote secondary blooms. Deadhead spent flowers promptly to keep the energy focused on new growth. Planting a mix of varieties with staggered bloom times will give you a longer flowering season.
In some cases, you may even get a third round of blooms if your climate allows. Prune with clean, sharp shears to prevent introducing disease. Removing yellowing or damaged leaves also helps the plant focus on flower production. Pruning isn’t just maintenance—it’s a strategy for abundance.
9. Divide and Transplant When Needed
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My favorite gardeners on Instagram are Greg & Joe from The Front Gardeners in Suffolk, England. They know how to grow delphiniums! The above clip explains perfectly how you can divide your delphiniums. Give them a follow.
Delphiniums benefit from division every few years to prevent overcrowding and keep them vigorous. My take is to divide in early spring by lifting the plant and carefully separating the roots. You can pot up new divisions until they’re well-rooted or plant them directly into the garden with enough space to thrive.
Transplanting after division gives new sections time to settle before summer heat arrives. Make sure each division has at least one strong shoot and a healthy portion of root. Water well after transplanting and provide a bit of shade if the sun is intense. Regular division rejuvenates plants and gives you more delphiniums to spread around.
10. Prepare for Winter
Winter care is all about protecting delphiniums from root exposure due to soil heaving. Apply a generous layer of mulch around the base in late fall, then remove it in spring to allow fresh growth and reduce slug damage.
In areas with harsh winters, consider cutting back stems to just a few inches above ground after the first frost. This keeps the crown protected and reduces overwintering pests. Avoid using heavy mulch like bark, which can hold too much moisture. A light straw or leaf mulch works best to insulate without suffocating.
Final Thoughts
Delphiniums are the show-stoppers of the garden—there’s nothing quite like their towering blooms in shades of blue, purple, pink, and white. With the right care, soil, and sunlight, you’ll be rewarded with a stunning floral display year after year. Grow them with love, and they’ll return the favor in spectacular style.
Frequently Asked Questions About Growing Delphiniums
Are delphiniums difficult to grow?
They can be a little fussy at first, but once you understand their preferences—cooler temps, rich soil, and some afternoon shade—they’re surprisingly rewarding. After 30 years of growing them, I can say they’re absolutely worth the extra effort!
What’s the best time to plant delphiniums?
Early spring is ideal, once the soil has warmed but before the heat of summer sets in. You can also plant in early fall, allowing at least six weeks before your first frost for roots to establish.
Do delphiniums need full sun?
They love sun—but not too much. Aim for at least six hours of morning sunlight with protection from intense afternoon rays, especially in warmer climates.
How often should I water delphiniums?
Keep the soil consistently moist, especially during dry spells. Water at the base to avoid wetting the foliage, which can lead to disease.
Should I stake my delphiniums?
Yes, especially the taller varieties like Pacific Giants. Stake early, before the stems become too tall, to prevent bending or breakage.
What kind of soil do delphiniums prefer?
Fertile, well-drained, slightly alkaline soil is best. Amending your garden beds with compost or aged manure will help boost growth and bloom quality.
What pests or diseases affect delphiniums?
Watch for aphids, slugs, spider mites, powdery mildew, and crown rot. Good airflow, proper watering techniques, and a tidy garden will go a long way toward prevention.
Can I grow delphiniums in warmer climates?
Yes, but choose heat-tolerant types like Delphinium chinensis or Delphinium consolida. These varieties are more forgiving in hot weather.
How do I encourage more blooms?
Prune spent flower spikes to a set of leaves to promote a second flush. With the right conditions, you might even get a third round of blooms.
When and how should I divide delphiniums?
Every few years, divide them in early spring. Gently lift the clump, separate the roots, and either replant directly or pot up divisions to grow on before transplanting.
