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How To Grow Delphiniums

Delphiniums from New Zealand. Variety is Cobalt Blue

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Delphiniums, with their striking, towering spikes of colorful flowers, are a favorite among gardeners and my personal favorite as well. They are truly splendid! These perennial beauties can add a touch of elegance and charm to any garden. The most common question I get is “How do you grow Delphiniums?”. Well, let me help you! I’ll walk you through the steps to grow thriving delphiniums for your own garden. When growing Delphiniums, you need to consider many factors, from selecting the right varieties to providing optimal care throughout the growing season.

Choosing the Right Delphinium Varieties

How to grow Delphiniums.Not all delphiniums are created equal. The first step to success is selecting the right varieties for your garden. Here are my favorites.

I’ve always loved the tall Pacific Giants Delphinium for their consistent colors and ease of germination. But they are incredibly tall! My Pacific Giants reach heights of over 6 feet. You will definitely want to stake them. One good gust of wind or heavy rain will break the bloom stalks in two!

If you are not the type to be on top of that then Magic Fountain Delphiniums are just as lovely but shorter and therefore more manageable at 3-4 Ft. Magic Fountains come in a range of colors, including shades of blue, lavender, pink, and white. The flowers are often bi-colored or have a contrasting eye.

There is also the newcomer on the Delphinium scene: New Zealand Delphiniums. They breed both shorter and taller varieties in amazing colors with much stronger stems. The flowers can be single or double, and they often have a distinctive white or contrasting “bee” in the center.

Delphiniums are hardy from zone 3-8. That covers most of the United States except for the warmest areas of the country. For those warm areas, your best bet would be the very short varieties of Delphinium chinensis or the annual reseeding Delphinium consolida or Larkspur. Of those two heat tolerant delphiniums, I grow “Blue Butterfly” and “Giant Imperial”. For information on starting Delphiniums from seed, go to my article Growing Delphiniums From Seed.

Selecting the Ideal Location

blue DelphiniumsDelphiniums thrive in specific growing conditions, and choosing the right location is crucial for their health and optimal development. Here are some key considerations for selecting the best location to grow them:

Sunlight: Delphiniums crave sunlight but also need protection from scorching afternoon rays. Choose a location that receives at least 6 hours of direct sunlight per day. I think many people who have problems growing Delphiniums have a site that is too warm during the summer months. Even here in upstate NY where summer nights are usually cool, I like to grow mine in places that are shaded from the late afternoon sun.

Soil: Well-drained soil is essential for delphiniums. They do best in fertile, loamy soil with good drainage. Heavy or waterlogged soil can lead to root rot and other issues. Amending the soil with organic matter can improve its structure and drainage.

Air Circulation: Good air circulation helps prevent fungal diseases, which can be a concern for delphiniums. Plant them with enough spacing to allow air to flow freely between the plants. Avoid overcrowding.

Protection from Wind: Delphiniums are tall and can be susceptible to wind damage. Planting them in a location where they are protected from strong winds or providing staking for support can help prevent breakage.

Soil Preparation

Delphinium New Zealand Pagan Purple is a hybrid Delphinium with exceptionly strong stems.There is nothing more important than preparing the soil correctly before planting to ensure your delphiniums have a healthy foundation from the very start. They prefer fertile, well-drained soil with a slightly alkaline pH. Where I live, the soil couldn’t be any worse for growing them. We have heavy clay soil, and it’s very poorly drained. We created raised beds and incorporated tons of organic matter from compost, to improve soil structure and fertility.  Adding well-rotted compost or aged manure to the soil can be a game-changer. They are heavy feeders so not only does the compost provide nutrients, it also allows the root system to flourish and grow deep down.

Planting Delphiniums

Plant delphiniums in early spring when the soil is warm. You can transplant them in the fall as well but spring is my preferred time.  I dig a hole at least twice the size of the root ball and place the plant at the same depth it was in its container. Space multiple plants at least 2 to 3 feet apart to allow for proper air circulation. Water thoroughly after planting to help settle the soil. When the plants are young it’s critical to keep a daily eye on them until they are established.

Watering and Fertilizing

Pink purple and blue DelphiniumsDelphiniums appreciate consistent moisture, especially during dry spells. Water at the base of the plant to keep foliage dry, as wet leaves can lead to diseases. I don’t usually add fertilizer because the soil is already so rich in nutrients but if you have doubts about your own soil fertility you can apply a balanced, slow-release fertilizer in spring when new growth appears. Avoid Excessive Nitrogen: While nitrogen is essential for foliage growth, excessive amounts can lead to lush foliage at the expense of flowers. Choose a balanced fertilizer to avoid this issue. Avoid over-fertilizing, as this can result in weak, leggy stems as well.

Providing Adequate Support

Delphiniums Pacific Giants

Materials Needed:

  • Sturdy stakes (bamboo are commonly used and readily available)
  • Twine or soft ties
  • Garden pruners

Procedure:

Choose the Right Stakes: Select sturdy stakes that are tall enough to support the anticipated height of your plant variety. Stakes should be inserted into the ground before the plants reach their full height.

Insert Stakes Early: Place the stakes in the ground early in the growing season, preferably when the delphiniums are still young and have not reached their full height. This allows the plants to grow and intertwine with the stakes.

Position Stakes Around Plants: Position the stakes evenly around the base of the plant. For a single plant, three or four stakes placed in a circle around the plant can provide adequate support.

Tie Stems to Stakes: As the delphiniums grow, loosely tie the main stems to the stakes using twine or soft ties.

Avoid Tying Too Tightly: Be cautious not to tie the stems too tightly. Leave some slack to allow for natural movement and growth. Tying too tightly can damage the stems and limit flexibility.

Adjust as Needed: Regularly check the ties and adjust them as needed. As the plants continue to grow, you may need to add additional ties or adjust the existing ones to accommodate the increasing height and weight of the flower spikes.

Remove Stakes After Flowering: Once the delphiniums have finished flowering, you can remove the stakes. However, if your region experiences strong winds, you may want to keep the stakes in place until the end of the growing season to provide support.

Staking is a preventive measure that helps maintain the upright growth and ensures that the tall flower spikes remain visually striking in the garden. It is worth the effort!

Pest and Disease Management

Growing Delphiniums from seed.Keep an eye out for pests and diseases if you want to maintain healthy delphiniums. I haven’t had many problems over the years but here are some common pests and diseases that can affect them, along with management strategies:

Common Pests

Aphids:

Use insecticidal soap or neem oil to control aphids. Introduce natural predators like ladybugs. Regularly inspect plants for early detection.

Snails and Slugs:

Remove debris and create barriers, such as copper tape, to deter snails and slugs. Apply iron phosphate-based baits as a more environmentally friendly option.

Spider Mites:

Keep the plants well-watered to reduce mite populations. Use a strong stream of water to hose down the delphinium plants, particularly the undersides of leaves. This can help physically remove spider mites. Use of insecticidal soap or neem oil helps. If the infestation is severe, consider using a miticide. Choose a miticide labeled for use on delphiniums and follow the instructions carefully. Keep in mind that repeated use of miticides can lead to resistance in spider mites, so use them judiciously.

Common Diseases

Delphinium Guardian has stunning purple and blue petals.The most common diseases of Delphiniums are Powdery Mildew, Botrytis Blight (Gray Mold), leaf spot, root rot and crown rot. Here are some tips to prevent and manage all these diseases on delphiniums:

Ensure proper spacing between delphinium plants to promote good air circulation. Adequate spacing reduces the likelihood of humidity buildup, which can contribute to delphinium diseases.

Water the plants at the base rather than overhead to keep the foliage dry. Watering in the morning allows the plants to dry out during the day, reducing the risk of disease.

Remove and discard infected plant material. Improve air circulation, and avoid overhead watering. Apply fungicides preventatively during humid conditions.

Consider applying fungicides labeled for disease control if the problem persists. Fungicides containing sulfur, neem oil, or potassium bicarbonate can be effective. Always follow the instructions on the product label.

Pruning Delphiniums

Pruning is essential for encouraging bushier growth and prolonging the blooming period. I’ve had some years where there were always some Delphiniums blooming. That is a real treat! My advice is after the initial bloom, cut back the flower spikes to a set of leaves to encourage secondary flowering. Deadhead spent blooms promptly to redirect energy into the development of new buds.  I grow lots of different varieties because their bloom time will vary as well helping to keep the blooms coming.

Dividing and Transplanting

Deep Blue Delphinium with a dark bee.

Delphiniums benefit from division every few years to maintain vigor and prevent overcrowding. It’s best to divide the plants in early spring. Lift the entire plant, separate the crown and roots, and replant the divisions with adequate spacing. Personally, I like to put new divisions in a pot and let the roots fill out the container before transplanting. The original plant should still be big enough to transplants back directly without it suffering from any shock.

Winter Care Of Delphiniums

It’s not the cold temperatures that are hard on Delphiniums in winter but the heaving of plants as the soil freezes which will expose the roots. You can apply a layer of mulch around the base of the plants in late fall to protect them but I like to remove the mulch in spring for unimpeded growth and less slugs.

In a Nutshell

Delphinium flowers are show-stoppers! There is nothing more satisfying in the flower gardening world than to grow magnificent Delphinium plants! They can transform your garden into a vibrant and colorful oasis. Their shades of blue  are like no other flowers. By following the steps outlined here, from selecting the right varieties to providing proper care throughout the seasons, you can enjoy the beauty of these majestic flowers year after year. Remember to adapt these guidelines to your specific climate and soil conditions for the best results. Happy gardening!

FAQ – How To Grow Delphiniums

How do I choose the right delphinium varieties for my garden?

Consider factors like your climate zone and garden size. Popular varieties include Pacific Giants for consistent colors, Magic Fountains for manageable height, and New Zealand hybrids for strong stems and vibrant colors.

What is the ideal location for planting delphiniums?

Choose a spot with at least half a day of sunlight but protect them from scorching afternoon rays. Avoid low-lying areas prone to water accumulation to prevent root rot.

How can I prepare the soil for delphiniums?

Delphiniums prefer fertile, well-draining soil with a slightly alkaline pH. Improve soil structure and fertility by incorporating organic matter like compost, especially in poorly drained soil.

When is the best time to plant delphiniums?

Plant in early spring when the soil is warm. Dig a hole twice the size of the root ball, maintain proper spacing, and water thoroughly after planting.

How should I water and fertilize delphiniums?

Provide consistent moisture, especially during dry spells. Water at the base to keep foliage dry. Use a balanced, slow-release fertilizer in spring if needed, but avoid over-fertilizing.

How can I prevent delphiniums from toppling over?

Support tall flower spikes early in the growing season with sturdy stakes and gentle ties to prevent them from falling.

What are common pests and diseases affecting delphiniums?

Common pests include aphids, snails, slugs, and spider mites. Diseases include powdery mildew, botrytis blight, crown rot, leaf spot diseases, and root rot. Use appropriate management strategies outlined in the guide.

Why is pruning important for delphiniums?

Pruning encourages bushier growth and prolongs the blooming period. After the initial bloom, cut back flower spikes to a set of leaves to promote secondary flowering. Deadhead spent blooms promptly.

How and when should I divide and transplant delphiniums?

Divide every few years in early spring. Lift the entire plant, separate the crown and roots, and replant divisions with adequate spacing. Consider potting new divisions before transplanting.

How can I care for delphiniums during winter?

Apply a layer of mulch in late fall to protect against soil heaving. Remove mulch in spring for unimpeded growth. Adapt winter care to your specific climate.

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Welcome Gardening Friends!
Amanda in Greenhouse with blooming Delphiniums. She loves growing flowers!

Amanda Shenstone

Flower Lover, Grower, Gardener

As part of Graceful Gardens for decades, I’ve garnered a wealth of knowledge about growing Delphiniums, perennials and annual flowers, and I am eager to share these insights with all of you.

Amanda Shenstone

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