Delphinium ajacis
Delphinium ajacisUSDA | Grow Zone
3-7Outdoors all year in zones 3 to 7. Anywhere colder, keep it as a houseplant. Protect it below 32°F.
- Light
- Full sun, 6-8 hours
- Water
- Consistently moist soil
- Humidity
- 40-60%
- Temperature
- 60-75°F
- Difficulty
- Intermediate
- Growth
- Moderate
- Mature size
- 3-5 ft tall, 1-2 ft wide
- Pets
- Toxic to pets and humans
Delphinium ajacis, commonly known as larkspur, is a striking perennial known for its tall spikes of vibrant flowers. Native to Europe, it adds a splash of color to gardens and is favored for its beauty and ability to attract pollinators.
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Ideal temperature
60-75°F is where it grows fastest. Below 32°F cold damage starts.
Spacing and harvest
- Mature size
- 3-5 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 ajacis prefers consistently moist soil but should not be waterlogged.
Water deeply once a week, increasing frequency during hot weather. 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, requiring at least 6-8 hours of direct sunlight daily.
Ideal placement is in a location that receives morning sun and afternoon shade in hotter climates, as it can tolerate partial shade but may not flower as abundantly.
Soil
Delphinium ajacis prefers well-draining, loamy soil with a pH range of 6.0 to 7.0.
A mix of garden soil, compost, and sand is recommended to ensure good drainage and nutrient availability.
Humidity
This plant enjoys moderate humidity levels, ideally between 40% and 60%.
To increase humidity, mist the leaves or place a humidifier nearby. Signs of humidity stress include browning leaf tips and stunted growth.
Temperature
Delphinium ajacis thrives in temperatures between 60-75°F (15-24°C) and is hardy in USDA zones 3-7.
It can tolerate light frost but should be protected from extreme heat, which can lead to wilting.
Fertilizing
Use a balanced fertilizer with an NPK ratio of 10-10-10, applying every 4-6 weeks during the growing season.
Signs of nutrient deficiency include yellowing leaves and poor flowering, indicating a need for more nutrients.
Pruning
Prune Delphinium ajacis in early spring to remove dead or damaged stems.
Use sharp, clean pruning shears to cut back to the base. Deadheading spent flowers throughout the blooming season encourages more blooms and prevents self-seeding.
Repotting
Repot every 2-3 years or when the plant becomes root-bound.
Choose a pot that is 1-2 inches larger in diameter. Signs it needs repotting include roots growing out of the drainage holes and stunted growth. Carefully remove the plant from its pot, trim any damaged roots, and place it in fresh soil.
Propagation
Propagation can be done through seeds or division.
For seeds, sow them in early spring indoors or directly in the garden after the last frost. For division, carefully dig up established plants in early spring or fall, ensuring each division has roots and shoots.
When it's unhappy
Yellow leaves
Why it happens
This can be caused by over-watering or nutrient deficiency.
How to fix it
Check soil moisture levels and adjust watering accordingly. Fertilize if nutrient deficiency is suspected.
Root rot
Why it happens
Over-watering and poor drainage can lead to root rot.
How to fix it
Ensure the pot has adequate drainage and reduce watering frequency. If root rot is present, remove the plant from the pot, trim away affected roots, and repot in fresh soil.
Wilting
Why it happens
Wilting can occur due to under-watering or extreme heat.
How to fix it
Check soil moisture and water deeply if dry. Provide shade during the hottest part of the day if temperatures exceed 85°F (29°C).
Powdery mildew
Why it happens
High humidity and poor air circulation can lead to powdery mildew.
How to fix it
Improve air circulation around the plant and apply a fungicide if necessary. Water at the base of the plant to keep leaves dry.
Stunted growth
Why it happens
This may be due to nutrient deficiency or poor soil conditions.
How to fix it
Fertilize with a balanced fertilizer and ensure the plant is in well-draining soil.
Care through the year
Spring
In spring, prune back any dead stems and prepare the soil by adding compost. This is also the best time to sow seeds or divide existing plants.
Summer
During summer, ensure consistent watering and deadhead spent flowers to encourage continuous blooming. Monitor for pests and diseases, especially powdery mildew.
Fall
In fall, after the first frost, cut back the foliage to prevent disease. Mulch around the base to protect roots during winter.
Winter
In winter, protect the plant from severe cold by applying mulch. If in a pot, consider moving it to a sheltered location to prevent frost damage.
Toxicity & Safety
Delphinium ajacis is toxic to pets and humans if ingested, particularly the leaves and seeds. Symptoms of ingestion include nausea, vomiting, and in severe cases, respiratory distress.
Good to know
Why are my Delphinium ajacis leaves turning yellow?
Yellow leaves on Delphinium ajacis can indicate over-watering or a nutrient deficiency. Check the soil moisture and adjust watering, and consider fertilizing if the plant lacks nutrients.
How often should I water my Delphinium ajacis?
Water your Delphinium ajacis deeply once a week, increasing frequency during hot weather. Ensure the soil remains consistently moist but not soggy.
What is the best soil for Delphinium ajacis?
Delphinium ajacis prefers well-draining, loamy soil with a pH of 6.0 to 7.0. A mix of garden soil, compost, and sand is ideal for healthy growth.
How can I propagate Delphinium ajacis?
You can propagate Delphinium ajacis through seeds or division. Sow seeds in early spring or divide established plants in spring or fall for new growth.
What should I do if my Delphinium ajacis is wilting?
If your Delphinium ajacis is wilting, check the soil moisture. Water deeply if the soil is dry, and provide shade during extreme heat to prevent further stress.
When should I prune my Delphinium ajacis?
Prune Delphinium ajacis in early spring to remove dead or damaged stems. Regular deadheading throughout the blooming season will also encourage more flowers.
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