Siberian Larkspur
Delphinium grandiflorumUSDA | Grow Zone
3-7Outdoors all year in zones 3 to 7. Anywhere colder, keep it as a houseplant. Protect it below 30°F.
- Light
- Full sun to partial shade
- Water
- Deeply once a week
- Humidity
- 40-60%
- Temperature
- 60-75°F
- Difficulty
- Intermediate
- Growth
- Moderate
- Mature size
- 3-4 ft tall, 1-2 ft wide
- Pets
- Toxic to pets and humans
Delphinium grandiflorum, commonly known as Siberian Larkspur, is a striking perennial known for its tall spikes of vibrant blue flowers. Native to Siberia, this plant adds a stunning visual element to gardens and attracts pollinators, making it a favorite among gardeners.
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Ideal temperature
60-75°F is where it grows fastest. Below 30°F cold damage starts.
Spacing and harvest
- Mature size
- 3-4 ft tall, 1-2 ft wide
- Plant apart
- 12-24 in
- Frost
- Half hardy: light frost only
Everything it needs
9 essentials at a glance
Watering
Delphinium grandiflorum prefers consistently moist soil, especially during its active growing season in spring and summer.
Water the plant deeply once a week, ensuring the top inch of soil dries out between waterings. In hotter months, you may need to increase frequency. Signs of over-watering include yellowing leaves and root rot, while under-watering may cause wilting and browning leaf edges.
Light
This plant thrives in full sun to partial shade, ideally receiving at least 6 hours of direct sunlight daily.
In hotter climates, some afternoon shade can help prevent leaf scorch. It can tolerate light shade but may produce fewer flowers in such conditions.
Soil
Delphinium grandiflorum prefers well-draining, fertile soil with a pH range of 6.0 to 7.0.
A mix of loamy soil with added compost or peat moss is recommended to improve drainage and nutrient content. Ensure that the pot has drainage holes to prevent waterlogging.
Humidity
This plant enjoys moderate humidity levels, around 40-60%.
To increase humidity, mist the leaves regularly or place a humidity tray filled with water and pebbles beneath the pot. Signs of low humidity include browning leaf tips and poor flower production.
Temperature
Delphinium grandiflorum prefers cooler temperatures, ideally between 60-75°F (15-24°C).
It is hardy in USDA zones 3-7 and can tolerate light frost. However, extreme heat above 85°F (29°C) can stress the plant, leading to wilting and reduced flowering.
Fertilizing
Use a balanced fertilizer with an NPK ratio of 10-10-10 or a slow-release fertilizer in early spring as new growth appears.
Fertilize every 4-6 weeks during the growing season. Signs of nutrient deficiency include yellowing leaves and poor flowering.
Pruning
Prune Delphinium grandiflorum in late winter or early spring before new growth begins.
Remove any dead or damaged stems to encourage healthy growth. Deadheading spent flowers throughout the blooming season will promote additional flowering and improve the plant's appearance.
Repotting
Repot every 2-3 years or when the plant becomes root-bound.
Choose a pot that is 1-2 inches larger in diameter than the current one. Signs that it needs repotting include roots growing out of the drainage holes and stunted growth. Carefully remove the plant from its pot, loosen the roots, and place it in fresh potting mix.
Propagation
Propagation can be achieved through seeds or division.
For seeds, sow them in late winter or early spring, either indoors or outdoors after the last frost. Lightly cover the seeds with soil and keep them moist. For division, carefully dig up established plants in early spring or fall, ensuring each division has roots and shoots. Replant immediately in prepared soil.
When it's unhappy
Yellow leaves
Why it happens
Over-watering or nutrient deficiency.
How to fix it
Check soil moisture levels and adjust watering accordingly. Fertilize if nutrient deficiency is suspected.
Wilting
Why it happens
Under-watering or extreme heat.
How to fix it
Increase watering frequency and provide shade during the hottest part of the day.
Root rot
Why it happens
Poor drainage or over-watering.
How to fix it
Ensure proper drainage and reduce watering. If root rot is severe, consider repotting the plant in fresh soil.
Powdery mildew
Why it happens
High humidity and poor air circulation.
How to fix it
Improve air circulation around the plant and apply a fungicide if necessary.
Leggy growth
Why it happens
Insufficient light.
How to fix it
Move the plant to a sunnier location to encourage bushier growth.
Care through the year
Spring
In spring, focus on pruning dead stems and fertilizing as new growth appears. Ensure that the plant receives adequate water as it begins to bloom.
Summer
During summer, monitor for pests and diseases, and water regularly to keep the soil moist. Deadhead spent flowers to encourage more blooms.
Fall
In fall, after flowering has finished, cut back the foliage to the ground. Consider applying mulch to protect the roots during winter.
Winter
In winter, protect the plant from extreme cold by covering the base with mulch. Avoid watering unless the soil is completely dry.
Toxicity & Safety
Delphinium grandiflorum is toxic to pets and humans. All parts of the plant contain toxic alkaloids, which can cause symptoms such as nausea, vomiting, and diarrhea if ingested. Keep this plant out of reach of children and pets.
Good to know
Why are my Delphinium grandiflorum leaves turning yellow?
Yellow leaves can indicate over-watering or nutrient deficiency. Check the soil moisture and adjust your watering schedule, and consider fertilizing if necessary.
How often should I water my Siberian Larkspur?
Water your Delphinium grandiflorum deeply once a week, allowing the top inch of soil to dry out between waterings. Adjust frequency based on weather conditions.
What is the best soil for Delphinium grandiflorum?
This plant prefers well-draining, fertile soil with a pH of 6.0 to 7.0. A mix of loamy soil with compost or peat moss is ideal.
How can I propagate Delphinium grandiflorum?
You can propagate this plant through seeds or division. Sow seeds in late winter or early spring, or divide established plants in spring or fall.
What should I do if my Delphinium grandiflorum is wilting?
Wilting can be a sign of under-watering or extreme heat. Increase watering frequency and provide some afternoon shade to help the plant recover.
When should I prune my Siberian Larkspur?
Prune Delphinium grandiflorum in late winter or early spring before new growth appears. Remove any dead or damaged stems to promote healthy growth.
Is Delphinium grandiflorum toxic to pets?
Yes, all parts of Delphinium grandiflorum are toxic to pets and humans. Ingestion can cause nausea, vomiting, and diarrhea, so keep it out of reach.
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