The Best Way to Grow Dahlias, Our Step-by-Step Guide

Jane Westoby

Mar 25, 20243 min read

Updated: Mar 6

How to Grow Dahlias for Stronger, Earlier Blooms

If you haven't started your dahlias yet—now's the time! With the days getting longer and the soil warming up, these flower powerhouses are ready to wake up. Whether you’re a seasoned grower or just starting out, getting dahlias off to a strong start makes all the difference in their health, resilience, and blooming potential.

Should You Plant Dahlias Directly in the Ground?

Dahlias can be planted straight into the flower bed once the risk of frost has passed—but is it the best option? Here’s what to consider:

Pros of Direct Planting:

Saves space indoors—ideal if you don’t have a greenhouse or windowsills full of plants.
No need for transplanting—simply plant them where they will flower.

Cons of Direct Planting:

Timing: You’ll need to wait 6-8 weeks longer, as dahlias are not frost-hardy.
Slug Magnet: New shoots are tender and irresistible to slugs—early losses can be high.
Spring Flowers Still in Bloom: If you have other flowers in the same bed, you might not have space yet.
Uneven Growth: Some tubers sprout later than others, leaving gaps in your display.
No Early Cuttings: If you want to propagate more plants, starting indoors is best.

If direct planting is your only option, just be ready to protect new shoots from frost and slugs.

Why I Start My Dahlias Indoors (And How You Can Too!)

I start my dahlias indoors in March to get a head start on the season. I’m based in Hampshire (Zone 9), with our last frost date around mid to late April. While I could start earlier, low light levels mean they’ll struggle without grow lights—so I wait until the light is strong enough to produce sturdy, healthy plants.

Step 1: Wake Up the Tubers

I bring my dahlia crates indoors ( Inside the house) for 2- 4 weeks before potting them up. The warmth indoors kickstarts their growth, encouraging eyes to develop before planting.

Step 2: Potting Up for Early Growth

Once they show signs of life:

Unpack and pot them up into trays or pots (size depends on the tuber).
Use a little compost—they don’t need to be fully buried.
Leave the crown exposed to prevent rot and keep an eye on new shoots.
Water lightly—damp, not soaking, to encourage strong root development.

Not all tubers will be viable—I split mine down as far as I can, so some naturally won’t have eyes. The ones that sprout? Those are the keepers.

Step 3: Managing Growth & Taking Cuttings

Once shoots reach a few centimetres tall, I decide whether to take cuttings.

Prolific growers get cuttings—more plants, more blooms!
Tubers with only 2-3 shoots are left to grow out naturally.

Step 4: Keeping Them Frost-Free

Dahlias do not tolerate frost, so I keep them in a mini greenhouse, on windowsills, in the garage, sunroom, or greenhouse—wherever I have frost free space!

On warm, sunny days, I move them outside for real sunlight.
At night, they come back indoors to avoid frost damage.
Once they hit 10cm tall, I pot them up deeper into individual pots for stronger root systems.