How to Grow and Care for Dahlias

Dahlias are stunning flowers that bloom from midsummer to the first frost, offering a dazzling array of colors and forms. With varieties ranging from petite pompoms to giant "dinner plates," they add vibrant beauty to any garden. While they require specific care, including full sun and well-drained soil, their breathtaking blooms make the effort worthwhile for many gardeners.

• Common Names: Bedding Dahlia, Dahlia
• Scientific Name: Dahlia spp.
• Plant Type: Bushy, tuberous, herbaceous perennial plants
• Plant Height: 1-6 ft. tall
• Growing Time: 8-10 weeks
• Bloom Time: Summer, Fall
• Temperature: Plant when soil reaches 60ºF
• Hardiness Zone: 7-10 (Find your hardiness zone here)
• Sunlight: Full Sun
• Soil pH: 6.0 to 7.5
• Watering Frequency: Water 2-3 times a week
• Plant Spacing: 12 inches - 3 feet apart

Different Methods to Grow Dahlias

Growing from Tubers

Plant dahlia tubers outdoors in early spring after the last frost. Dig a hole 2 to 6 inches deep, place the tuber with the growing points facing up, cover with soil, and water after sprouts appear. Choose a sunny location and water weekly, increasing during dry spells.

• Pros: Established plants grow faster and produce more blooms.
• Cons: Requires digging up and storing tubers in colder climates.

Growing from Seeds

Fill a seeding tray with moist seed starting mix and press the seeds into the mix. Place the tray in a sunny window and keep the soil moist. Transplant seedlings into individual pots once sprouted, and move them outdoors when soil temperatures reach 65-70°F.

• Pros: Cost-effective and allows for seed collection from previous plants.
• Cons: Takes longer to mature and bloom, requiring more initial care.

Growing in Containers

Use a container at least 12 inches deep and wide with good drainage. Plant tubers or seedlings following the same depth requirements as ground planting. Place containers in full sun and stake stems for support. Water regularly and ensure soil remains damp.

• Pros: Portable and ideal for small spaces and patios.
• Cons: Requires frequent watering and larger containers for full growth.

Ideal Soil and Location Requirements

Dahlias thrive in rich, well-draining soil with a pH of 6.0 to 7.5. They require full sun, ideally 6 to 8 hours daily, and benefit from protection against strong winds. Amending heavy soil with compost or aged manure improves drainage and soil texture.

When to Plant Dahlias

Plant dahlias in late spring after the last frost, when soil temperatures reach 60°F. They bloom from midsummer to the first autumn frost. Ensure the danger of frost has passed before planting to protect the tubers. This timing ensures optimal growth and vibrant blooms throughout the season.

Growing Dahlias Outdoors

Planting dahlia tubers directly in the ground is the best method for growing these flowers outdoors. This approach is straightforward and avoids the need for indoor starting and transplanting. Here’s a step-by-step guide to help you grow dahlias in your garden:

1. Choose the right time. Plant dahlia tubers in late spring after the last frost when the soil temperature reaches 60°F (15°C).
2. Prepare the soil. Select a sunny location with well-draining soil. Amend the soil with compost or aged manure to improve its texture and fertility.
3. Dig the planting holes. For large dahlias, dig holes 6 to 8 inches deep and space them 3 feet apart. For medium dahlias, space them 2 feet apart, and for small dahlias, space them 12 inches apart.
4. Plant the tubers. Place the tubers in the holes with the growing points facing up. Cover them with 2 to 3 inches of soil.
5. Water after sprouting. Do not water immediately after planting. Wait until sprouts appear above the soil, then water thoroughly.
6. Stake tall varieties. Insert stakes at the time of planting to support taller dahlia varieties as they grow.
7. Maintain regular watering. Once established, water the plants 2 to 3 times a week, increasing during dry spells.
8. Fertilize regularly. Use a low-nitrogen fertilizer every 3 to 4 weeks from midsummer to early autumn to promote healthy growth and blooms.
9. Pinch and deadhead. Pinch off the top stem just above the highest set of branches once the tubers sprout. Regularly remove faded blooms to encourage more flowering.

Growing Dahlias Indoors

Growing dahlias indoors is possible, especially for medium- to dwarf-size varieties that thrive in containers. Here’s a step-by-step guide to help you grow dahlias indoors:

1. Choose the right container. Use a container that is at least 12 inches deep and wide, with good drainage.
2. Prepare the soil mix. Use a soilless mix combined with co-polymer moisture-retaining crystals, following the package instructions.
3. Plant the tuber. Place the tuber in the container with the growing points facing up. Cover it with a few inches of the soil-crystal mix.
4. Water sparingly. Spray water on the tuber until growth starts. Do not water if the soil is damp 1 inch below the surface.
5. Provide adequate light. Place the container in a sunny window where the plant can receive at least 6 hours of direct sunlight daily.
6. Fertilize regularly. Use a balanced fertilizer as directed on the package, typically every 3 to 4 weeks during the growing season.
7. Monitor growth. Add more soil if the roots become exposed. Ensure the plant remains stable and well-supported as it grows.
8. Maintain proper watering. Water the plant regularly, ensuring the soil remains damp but not waterlogged. Adjust watering frequency based on the plant's needs and indoor conditions.

Both dahlia flowers and tubers are edible. The tubers taste like a cross between a potato and a radish.

Caring for Dahlias

1. Watering: Dahlias need consistent moisture, so water them 2 to 3 times a week, especially during dry spells. Ensure the soil remains damp but not waterlogged to prevent root rot.
2. Fertilizing: Use a low-nitrogen, liquid fertilizer such as 5-10-10 or 10-20-20 every 3 to 4 weeks from midsummer until early autumn. This promotes healthy growth and vibrant blooms.
3. Pest Control: Common pests like aphids, caterpillars, and slugs can affect dahlias. Regularly inspect your plants and use natural treatments like neem oil or introduce beneficial insects to keep pests at bay.
4. Deadheading: Remove faded blooms regularly to encourage more flowering. This keeps the plant looking tidy and promotes continuous blooming throughout the season.
5. Harvesting: Cut dahlia stems in the morning before the heat of the day. Place the cut stems in a bucket of cool water, remove the bottom leaves, and arrange them in a vase. This ensures the flowers last longer, typically around 7 days.

Common Challenges With Dahlias

Growing dahlias can be a rewarding experience, but it does come with its challenges. In my experience, dahlias are not the easiest plants to grow, especially for beginners. They require well-draining soil, full sun, and consistent watering. Starting with tubers rather than seeds can make the process a bit simpler. However, they are quite resilient and can thrive with proper care, making them a favorite among many gardeners.

Common challenges when growing dahlias include dealing with pests like aphids, slugs, and caterpillars, as well as diseases such as powdery mildew and root rot. Overwatering can lead to stem rot, while underwatering can cause the plants to wilt. Additionally, dahlias are not frost-hardy and need to be dug up and stored in colder climates. Despite these hurdles, with a bit of attention and care, dahlias can produce stunning blooms that make the effort worthwhile.

Safety of Dahlias for Pets

Dahlias are toxic to cats, dogs, and horses, causing mild gastrointestinal issues and dermatitis. If you suspect your pet has ingested dahlias, contact the ASPCA 24-hour hotline immediately for assistance.

Frequently Asked Questions

How do I prevent my dahlias from getting powdery mildew?

Ensure good air circulation by spacing plants properly and avoiding overhead watering. Apply a fungicide if needed and remove any affected leaves to prevent the spread of the disease.

Can I grow dahlias in partial shade?

Dahlias prefer full sun but can tolerate partial shade. However, they may produce fewer blooms and grow less vigorously in shaded conditions.

How do I store dahlia tubers over winter?

After the first frost, dig up the tubers, dry them, and store them in a cool, dark, and frost-free place at 40º to 45ºF. Check occasionally for rot and remove any affected tubers.

What should I do if my dahlias are not blooming?

Ensure they receive at least 6 hours of sunlight daily, avoid over-fertilizing with nitrogen, and check for pests or diseases. Regular deadheading can also encourage more blooms.