Dahlia spacing: how far apart to plant dahlia tubers

dahlia spacing

Once you have decided when to plant out your dahlia tubers, you’ll need to think about your dahlia spacing – how far apart to plant the tubers. In this post, we’ll look at that question.

As with most things in gardening, how you space your dahlias will depend on your own particular circumstances. In particular, it depends on the type of dahlias you are growing, how you want them to look and what you are growing them for.

Dahlia spacing – cut flower and exhibition specimens

Let’s start with the conventional wisdom about how far apart to plant dahlia tubers. This spacing will give them the best chance of growing to their full potential. It is typically used by growers who are growing dahlias for cut flowers or exhibition.

These are the accepted distances for spacing dahlias if you are growing your dahlias in a good well-drained soil, in full sun – i.e. good conditions:

  • Plant dwarf bedding dahlias about 22cm to 30cm (9 to 12 inches apart;
  • Plant miniature, decorative or pompon dahlias about 35cm to 45cm (15 to 18 inches) apart;
  • Plant medium sized dahlias at least 60cm (2 feet) apart;
  • Plant large dahlias at least 90cm (3 feet) apart.

Traditional dahlia growers plant at these distances and set out their plants in rows. They allow some space for the grower to access the plant for staking, tying in and deadheading.

As indicated, this works well for producing good specimens. But it may not be so aesthetically pleasing if you want to use your dahlias as part of a mixed, and well-designed garden bed.

dahlia spacing - rows
Rows of Dahlias at Swan Island dahlias in Oregon. Image by kind permission of the National Dahlia Society

Dahlia spacing – mixed planting

Having got the conventional wisdom out of the way, I’ll be perfectly honest with you: I quite often get the spacing of my dahlias wrong and I often don’t follow the ‘rules’.

I don’t particularly grow dahlias for cut flowers and I don’t exhibit them.

In fact, my natural preference is for dense planting in my borders. I love to see borders where plants or groups of plants sit closely against each other, blending in to create a single multi-textured effect, with no soil visible between plants.

This can work, so long as you plan for the eventual size of the plants you are growing. You also need to accept that, with this style, you may not get the biggest and best examples of each individual plant.

In fact, the reality is that in general, the more densely you plant the less beneficial it is for the plants themselves. This makes sense when you realise that closely planted specimens are all competing for the same light, air, water, and soil nutrients.

The problem with this approach is that individual plants don’t always grow to the size you expect them to. Sometimes they’ll grow bigger and sometimes smaller. Often this is in response to weather, soil or other external factors such as the proliferation of pests and diseases.

And that’s why I sometimes get the spacing wrong and why sometimes I won’t get the effect I am looking for.

But to my mind, this is what gardening is about – growing plants you love, trying things out, sometimes failing, but trying again the following year.

Ultimately, you will decide for yourself whether you want your plants well-spaced or if you prefer a more naturalistic look. The beauty of gardening is that it is up to you – you can experiment and see what works best in your garden.

Summary: key spacing considerations for dahlias

In summary, here are the important factors to consider when working our how far apart you should plant your dahlias:

  1. Soil and climate: In well-drained soil, most dahlia tubers can be spaced 18-24 inches (45-60 cm) apart. However, if the soil is heavy or retains moisture, increase the spacing to 24-36 inches (60-90 cm). This will help prevent issues like rot and fungal diseases.
  2. Dahlia types: Different types of dahlias vary in size and growth habits. Smaller or dwarf varieties can be spaced closer together, around 12-18 inches (30-45 cm) apart. Larger or taller varieties need more room, approximately 24-36 inches (60-90 cm) apart.
  3. Display preferences: If you want a more compact and dense display, with the plants forming a lush, colourful mass, you can plant the tubers closer together. Aim for a spacing of 12-18 inches (30-45 cm) to achieve this effect.
  4. Air circulation: Good spacing between dahlia plants allows for better air circulation. This helps prevent diseases like powdery mildew. If you’re growing dahlias in an area with high humidity or have experienced disease issues before, use wider spacing, around 24 inches (60 cm) or more.
  5. Support requirements: Taller dahlia varieties may require additional support, such as stakes or trellises, to keep them upright. Providing wider spacing between tubers allows room for installing and securing these supports without crowding the plants.
  6. Mixed planting: If you’re planting dahlias in a bed or border alongside other plants, take account of the growth habits and spacing requirements of the other plants as well. Provide adequate spacing between different types of plants to avoid competition for resources and ensure each plant has sufficient room to grow.

More on Growing Dahlias

You can also get much more guidance on growing dahlias in these posts:

Love Dahlias?I've written the book on them

Check out my comprehensive step by step guide, with plain language explanations and ultra-useful images and illustrations. This is for you if you love dahlias and want to the best out of the dahlias you grow.

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