Are Dahlias Perennials or Annuals?

A Common Question Answered

By Hannah Miller at DIY Gardening

Hello, my name is Hannah Miller, and I’m the co-owner and contributor here at DIY Gardening.

Are dahlias perennials or annuals?

This is a common question.

Dahlias are technically tender perennials.

What does this mean?

Tender perennials such as dahlias will not survive winter frosts that penetrate into the ground, they can be grown as annuals in cold climates or as perennials in warmer zones.

Gardeners in almost any climate can grow dahlias as perennials by protecting them from the damaging frost.

The method and amount of winter protection will depend on where they are grown and, more specifically, how cold the climate is in winter.

Below I’ll explain how to protect dahlias so you can grow them as perennials, I will use the USDA Hardiness Zone system which you can see applied to a map of the UK and Ireland below:

Hannah Miller

Hannah Miller

UK plant hardiness map

The USA zone map can be viewed here.

Zone 7

Dahlias grown in zone 7 have little chance of surviving the winter if left in the ground.

The dahlia tubers will need to be lifted and stored in boxes for winter protection; they can be planted back into the garden come spring.

It’s unlikely that the tubers will survive outside, even with mulch to protect them.

The best place to store the dahlias would be in a garage or cellar or similar.

Dahlia tubers

Freshly dug dahlia tubers

Zone 8

Most of the UK is in Zone 8 and dahlias here should survive the winter provided the frosts are mild and it’s advisable to place at least 4″ (10cm) of mulch, straw, bark chips or similar over the soil.

Gardeners who wish to guarantee their dahlias will survive the frosts should lift and store them as per the advice for Zone 7.

Zone 9

As you can see from the map, Zone 9 covers warmer areas within the UK and Ireland and dahlias grown here will likely survive the winter and some basic protection should almost guarantee that.

4″ (10cm) of mulch or similar should be more than enough to protect the tubers from the frosts.

You shouldn’t need to lift and store the tubers, but some could still perish if the frosts are unusually severe for the region.

Zone 10

Dahlias grown in Zone 10 shouldn’t need lifting and won’t require any mulch or protection as the frosts in these regions are mild.

So Are Dahlias Perennials?

That depends on your climate and how you protect them.

If you want to play it safe, then lift and store the dahlias.

It’s impossible for me to predict the weather with 100% accuracy, but the zone map on this page gives you a good idea of whether you need to lift, mulch or just leave the dahlias as they are.

Dahlia blooms

How to Lift and Store Dahlias Over Winter

Lifting and storing dahlias doesn’t need to be difficult.

We’ve created an insightful guide, just follow our step by step instructions.

Dahlia tubers

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Dahlia growing guide

More From Hannah Miller:

This guide to perennial dahlias was created by Hannah Miller and was posted to our blog on the 14th of November, 2021.

Hannah is a keen amateur gardener, mother and a former NHS administrator.

She enjoys gardening as much as she cares about the environment and likes to share her knowledge with others.

More About Hannah Miller.

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