Dahlia Planting Distance | How to Space Dahlias for Stronger Growth and More Blooms

Introduction: Bigger Blooms Begin with Proper Spacing

Dahlias are one of the most spectacular flowering plants for summer gardens, offering an explosion of colour, structure, and variety from mid-summer until the first frost. Whether you’re growing dinner-plate dahlias for dramatic borders or pompom varieties for vibrant cut flowers, one crucial factor determines your success: planting distance.

Proper spacing ensures healthy growth, fewer pests, and abundant blooms. In this guide, you’ll learn the ideal dahlia planting distances for different types, plus expert tips on layout, soil prep, and aftercare.

1. Why Dahlia Spacing Matters

Spacing isn’t just about aesthetics — it directly affects:

• Air circulation, which reduces mildew and fungal diseases
• Access to light, helping all plants bloom evenly
• Ease of maintenance, including feeding, watering, and deadheading
• Root development and tuber size
• Preventing overcrowding, which can cause weak stems and smaller flowers

Well-spaced dahlias are healthier, more productive, and easier to manage all season long.

2. General Spacing Guidelines for Dahlias

The spacing you choose depends on the type and variety of dahlia you’re planting.

Between rows (if planting in beds):

• Space rows 60–90cm apart to allow easy access for maintenance and harvesting cut flowers.

3. How to Decide Your Spacing Based on Use

Cut Flower Gardens:

• Space dahlias closer (around 40–50cm apart) for long stems and manageable growth
• Stake or support plants early to prevent crowding

Garden Borders or Display Beds:

• Allow more room — 60–90cm apart for full shape and airflow
• Group by height and colour for best visual impact

Containers or Raised Beds:

• One tuber per large pot (at least 30–40cm wide and deep)
• In raised beds, treat as you would garden soil and use spacing based on variety size

4. When and How to Plant Dahlias Outdoors (UK Guide)

Planting time:

• Mid-to-late May, after the last frost
• In warmer areas, late April is fine with protection

Planting depth:

• Tubers: 10–15cm deep
• Sprouted dahlias: Level with soil surface, taking care not to bury stems

Mark your spacing before planting to keep layout neat and uniform.

5. Step-by-Step: How to Space and Plant Dahlias

1. Prepare the soil by loosening to 30cm deep and mixing in compost or well-rotted manure
2. Use a measuring stick or string line to space planting holes evenly
3. Dig holes based on tuber size and dahlia variety
4. Lay the tuber horizontally, eye (sprout) facing upwards
5. Cover with soil and water gently
6. Add plant supports now if needed — it’s easier before the plant grows tall
7. Label each plant with the variety name or colour

6. Soil and Site Tips for Well-Spaced Dahlias

Dahlias love:

• Full sun — at least 6 hours per day
• Well-drained soil, rich in organic matter
• Sheltered positions, away from strong winds

Avoid planting in:

• Shady areas (reduced blooming)
• Heavy, soggy soils (risk of rot)

Mix in horticultural grit if drainage is an issue. Raised beds work well for heavy soils.

7. Supporting Dahlias in Larger Plantings

Larger dahlias, especially dinner-plate varieties, benefit from early support.

Support tips:

• Use bamboo canes, metal rings, or tomato cages
• Place supports at planting time to avoid damaging roots
• Tie stems loosely with soft ties as they grow
• Keep rows accessible for pruning and harvesting

Well-spaced plants are easier to stake and manage through the season.

8. Companion Planting and Spacing Considerations

Good neighbours for dahlias include:

• Cosmos, zinnias, and rudbeckia (similar growth needs)
• Salvias and verbena bonariensis (attract pollinators)
• Marigolds (deter pests)

Avoid planting too closely with tall perennials that might shade them out.

Ensure each plant has space to access:

• Light
• Nutrients
• Airflow

9. Watering and Feeding Spaced-Out Dahlias

Watering:

• Water deeply once or twice a week
• Avoid overhead watering — it increases fungal risk
• Mulch to retain moisture and suppress weeds

Feeding:

• Start feeding when plants are 20–30cm tall
• Use a balanced feed first (10-10-10), then switch to high potash (e.g. tomato feed) when buds appear
• Feed every 2–3 weeks

Well-spaced plants have better access to soil nutrients and water — leading to stronger stems and better flowers.

10. What Happens If You Plant Dahlias Too Close Together?

Crowded dahlias may suffer from:

• Poor airflow, leading to mildew and disease
• Leggy or weak stems
• Small, fewer blooms
• More pest problems
• Difficulty in deadheading, feeding, and harvesting

It’s tempting to squeeze more in, but proper spacing leads to healthier, more floriferous plants in the long run.

11. Can You Plant Dahlias Closer for a Full Border Look?

Yes — for a massed border effect, you can reduce spacing to:

• 30–40cm for dwarf varieties
• 40–50cm for medium types

But be aware:

• You’ll need more frequent maintenance
• Risk of mildew and pests increases
• Plants may need more water and feeding

Use this style for show beds or short-season displays, and remove spent plants quickly to reduce disease risk.

12. Can You Move Dahlias After Planting?

You can — but it’s best to avoid disturbing them once established.

If you must move them:

• Do so early in the season (before flowering)
• Dig wide and deep to preserve roots
• Replant at the same depth, water well, and mulch

Once growing vigorously, it’s better to leave dahlias in place to avoid shock.

13. Growing Dahlias in Rows for Cut Flowers

For cut flower beds:

• Use 45–60cm spacing in rows 60cm apart
• Stake plants in lines with string or mesh
• Harvest blooms regularly to encourage more

Dahlias grown this way are highly productive, easy to access, and perfect for florists or home bouquets.

14. Lifting and Storing Dahlias After Flowering

Dahlias are tender perennials — in colder areas of the UK, they’ll need lifting and storing after the first frost.

Steps:

1. Cut stems down to 10–15cm
2. Carefully lift tubers with a fork
3. Shake off excess soil and allow to dry
4. Store in boxes of dry compost, wood shavings, or newspaper in a cool, frost-free place
5. Label each tuber to remember spacing needs next season

15. How to Plan Your Dahlia Layout

Use a simple sketch or garden planner. Consider:

• Height (back, middle, or front of border)
• Colour scheme
• Bloom size
• Access for deadheading and cutting
• Spacing for airflow and light

Group similar sizes together for easier maintenance and a cleaner look.

Conclusion: Give Your Dahlias the Space They Deserve

Dahlias reward proper spacing with bigger blooms, healthier plants, and a longer flowering season. Whether you’re growing them in neat rows for cutting or massing them in garden beds for colour impact, giving each plant room to grow is essential.

Remember: spacing isn’t lost space — it’s what allows each dahlia to thrive.

Top 10 FAQs: Dahlia Planting Distance

1. How far apart should I plant dahlias?

Spacing ranges from 30–90cm depending on the variety. Larger dahlias need more space.

2. What happens if I plant dahlias too close?

Overcrowding leads to poor airflow, weak stems, mildew, and fewer flowers.

3. Can I plant multiple dahlias in one pot?

Only if the pot is very large. Ideally, one dahlia per 30–40cm pot.

4. Can I reduce spacing for borders?

Yes — but monitor for disease and stake carefully to support growth.

5. How deep should I plant dahlia tubers?

10–15cm deep, with sprouts just below the surface.

6. Do taller dahlias need more space?

Yes — give tall varieties 75–90cm spacing for support and airflow.

7. How far apart should dahlia rows be?

60–90cm apart for easy access and good maintenance.

8. Can I grow dahlias closer together in greenhouses or tunnels?

Possibly — but ensure excellent ventilation and regular pruning.

9. When should I plant dahlias outdoors in the UK?

From mid-May, after the risk of frost has passed.

10. Can I plant dahlias closer for cut flowers?

Yes — 40–50cm apart works well with regular staking and cutting.