Discover the Key to Abundant Blooms: How to Grow Delphinium in a Greenhouse Like a Pro

Delphiniums, with their majestic spires of vibrant blooms, are a true spectacle in any garden. But did you know that you can cultivate these beauties even in the confines of a greenhouse? Growing delphiniums in a greenhouse offers you complete control over their environment, ensuring optimal conditions for healthy growth and abundant blooms. This guide will walk you through the process, from seed to stunning display, so you can enjoy these captivating flowers year-round.

Getting Started: Choosing the Right Delphinium Variety

The first step in your delphinium journey is selecting the right variety. There are numerous delphinium species and cultivars available, each with its own unique charm.

• Pacific Giant Delphiniums: These are the most popular choice for greenhouse cultivation, boasting towering spikes of large, double blooms.
• Elatum Delphiniums: These offer a more compact growth habit, reaching heights of 3-4 feet, making them suitable for smaller greenhouses.
• Belladonna Delphiniums: This variety is known for its airy, delicate blooms and graceful, branching stems.

Consider the size of your greenhouse and your desired aesthetic when making your selection.

Preparing Your Greenhouse for Delphiniums

Delphiniums thrive in well-drained, fertile soil with a slightly acidic pH (6.0-6.5). Before planting, prepare your greenhouse by:

• Sterilizing the soil: This eliminates any potential pests and diseases. You can achieve this by baking the soil in the oven at 180°F for 30 minutes or using a soil sterilizer.
• Enriching the soil: Mix in compost or well-rotted manure to improve drainage and nutrient content.
• Providing adequate drainage: Ensure your greenhouse pots or containers have drainage holes to prevent waterlogging.

Sowing Delphinium Seeds: A Step-by-Step Guide

1. Start Early: Delphiniums are best sown indoors in late winter or early spring. This allows them to establish a strong root system before being transplanted outdoors.

2. Use Seed Trays: Fill seed trays with a seed starting mix and gently press the seeds into the soil.

3. Cover Lightly: Sprinkle a thin layer of seed starting mix over the seeds.

4. Water Gently: Mist the soil with a fine spray bottle to keep it moist.

5. Provide Light: Place the trays in a bright location, but avoid direct sunlight.

6. Maintain Consistent Moisture: Keep the soil consistently moist, but not soggy.

7. Thin Seedlings: Once the seedlings have developed their first set of true leaves, thin them out, leaving the strongest seedlings spaced about 2 inches apart.

Transplanting Your Delphiniums: A Gentle Transition

Once the seedlings have developed several sets of true leaves and the weather has warmed up, it’s time to transplant them into larger pots or directly into the greenhouse beds.

• Choose the Right Pots: Select pots that are at least 12 inches in diameter and have drainage holes.
• Prepare the Pots: Fill the pots with a well-draining potting mix.
• Transplant Carefully: Carefully remove the seedlings from their seed trays and plant them in the pots, ensuring the root ball is covered with soil.
• Water Thoroughly: Water the transplanted seedlings well to help them establish themselves.

Providing Optimal Growing Conditions

• Light: Delphiniums thrive in bright, indirect light. Position them in a sunny spot in your greenhouse, but avoid direct sunlight during the hottest part of the day.
• Temperature: Maintain a greenhouse temperature of 60-70°F during the day and 50-60°F at night.
• Watering: Water your delphiniums regularly, ensuring the soil is consistently moist but not waterlogged.
• Fertilizing: Feed your delphiniums with a balanced liquid fertilizer every two weeks during the growing season.

Supporting Your Delphiniums: Preventing Flopping

Delphiniums are known for their tall, graceful stems. However, these stems can become top-heavy, especially as the plants mature and produce flowers. To prevent flopping, provide support:

• Staking: Use sturdy stakes and plant ties to support the stems as they grow.
• Cage Support: Create a cage around the delphiniums using wire mesh or chicken wire.

Enjoying Your Delphinium Blooms: A Symphony of Color

With proper care, your delphiniums will reward you with a breathtaking display of vibrant blooms.

• Deadheading: Remove spent flower stalks to encourage further blooming.
• Harvesting: Cut the flower stalks for bouquets or arrangements when they are fully open.

The Secret to Success: Protecting Your Delphiniums

• Pests: Watch out for aphids, spider mites, and slugs. Use organic pest control methods to keep them at bay.
• Diseases: Delphiniums are susceptible to powdery mildew and fungal diseases. Ensure good air circulation and avoid overhead watering to prevent these issues.

The Final Chapter: Enjoying Your Delphinium Harvest

Your greenhouse-grown delphiniums are a testament to your dedication and care. Enjoy their beauty in your greenhouse or share their vibrant colors with others by creating stunning bouquets or arrangements.

Answers to Your Most Common Questions

Q: How long does it take for delphiniums to bloom in a greenhouse?

A: Delphiniums typically take 12-16 weeks to bloom from seed.

Q: Can I grow delphiniums in a small greenhouse?

A: Yes, you can grow delphiniums in a small greenhouse. Choose compact varieties like Elatum delphiniums or consider growing them in pots to manage their size.

Q: How do I overwinter delphiniums in a greenhouse?

A: Delphiniums are generally not hardy in cold climates. In a greenhouse, you can protect them from frost by covering them with a frost blanket or moving them to a warmer location within the greenhouse.

Q: What happens if my delphiniums don‘t bloom?

A: Several factors can prevent delphiniums from blooming, including insufficient light, improper watering, lack of nutrients, or pest infestations. Review the care instructions and address any potential issues.

Q: Can I grow delphiniums in a cold frame?

A: Yes, you can grow delphiniums in a cold frame, but they may need additional protection from frost during the winter.