Dahlias are wonderful flowers which feature in many UK gardens thanks to their beauty, colour, and variety. Find out my answers to Google’s most asked questions on this flower.

Where are Dahlias native to?

Dahlia are native to Mexico, and they are in fact the national flower of the country. Their rich history in South America dates back as far as the Aztec empire. The original Aztec name for the plant translates to ‘water pipe flower.’ This is because the stem of the Dahlia imperialis would be hollowed out and used to transport water.

The modern name, Dahlia, was chosen to honour the scientist Anders Dahl in 1791.

Aztec pyramid mexico

Are Dahlias perennials?

Yes, they are perennials. Specifically, they are tender perennials, which means they require protection from freezing temperatures.

Which garden style are they best suited for?

Dahlias work well in most garden styles. They do well in cottage garden-inspired borders, and also in Mediterranean or tropical garden designs too.

Growing dahlias in a sunny spot

How do you grow Dahlias from seed?

Though it is possible to grow Dahlias from seed, they are often started as tubers and grown that way.

If you are trying to grow from seed, sow them between February and April in 0.5cm deep trays of moist, peat-free compost. Make sure to leave them in a warm position, preferably between 15 and 20 degrees Celsius, and under cover to protect from cooler temperatures.

You can then transplant the dahlias to small pots once the seedlings are large enough to handle. Once the risk of frost has passed, around May to June, garden off your young plants gradually. Then plant them out in your garden.

Dahlia tubers growing from seeds

How long do Dahlias take to germinate from seed?

A Dahlia will typically germinate between 10 days to a fortnight (14 days). This might happen quicker if they are growing in a warm environment, between 15 and 20 degrees Celsius.

Flowers should appear as soon as 10 weeks after sowing, depending on the weather.

What are seeds vs tubers?

A dahlia tuber is harvested off a parent plant, meaning you what you grow will be identical. You know exactly what you’re getting.

Seeds result in random specimens, based on genetics and pollination. You won’t know the size or colour of your dahlia until they flower.

Are Dahlias easy to grow?

Relatively easy, yes, particularly when you are growing from dahlia tubers.

This is as simple as planting tubers into peat-free multi-purpose compost, and water in. Start off in a greenhouse if you wish, and the shoots will appear after 2-3 weeks.

dahlia easy to grow

How and where do Dahlias grow best?

Dahlia love to be in fertile, well-draining soil. They prefer to be in a sunny location.

Make sure to leave space between plants to allow growth for larger cultivars – a good gauge is about 60cm.

Plant out tubers in late May or early June if your area is prone to late cool temperatures. If you have purchased grown plants in containers, plant them out straight away.

Dahlias like watering regularly, so water well in dry and hot weather. And regularly water if growing in containers.

Apply granular general-purpose fertiliser once planted. This is key to encouraging flower-laden stems and big leafy plants. If you want to boost flowering, use potassium-rich liquid fertiliser from early June to early September.

And smaller varieties, that grow up 50cm, are great in containers. Try Dahlia ‘Gallery Vincent’, Dahlia ‘Moonfire’, and ‘Marie Schnugg’. If you are growing in containers, feed them once a week.

How long do Dahlia plants live for?

Generally, perennials live for at least three years – Dahlias but they can last for many years if they are cared for under the right conditions.

How big do they grow?

Depending on the variety, Dahlias range in height from 40cm to over 6ft (such as Dahlia ‘Chat Noir’).

And the blooms can range in diameter from 5cm to 30cm.

Dahlia chat noir

How long do Dahlias flower for?

A general rule of thumb is 120 days, or 4 months.

And they can be in bloom from July to October. Deadheading will encourage more flowering, I’ll get into when and how you do that in a bit.

Are Dahlias good for bees?

Dahlias are loved by various pollinators, including bees, and butterflies. Single-flowered dahlias are better for pollinators, as the pollen is easier to access.

Dahlia with a bee

Are Dahlias frost hardy?

Dahlias are not frost-hardy.

The foliage will be killed off by the frosts of autumn and winter. So, keep up to speed with the weather in your area, from September.

You can leave the tubers in the ground or remove them and store them somewhere frost-free over the winter, once the foliage has started to die down.

How to lift and store tubers

Dig around the clump and lift the tubers with a fork. Take care not to damage them. Shake as much soil off as possible, then, using secateurs, cut down the dahlia stems and compost the leaves.

Use a hose or bucket of water to rinse the tubers and stand them upside down to dry. Once dry, pack them in a box or pot and cover them with dry compost, (any moisture could lead to rot).

You can also store them in vermiculite, or wrap them in dry newspaper.

What colours do Dahlias come in?

Dahlias come in pretty much any colour for flowers that you can think of. These include: red, white, orange, yellow, pink, purple, and lavender.

You can also get Dahlias that have multiple colours in their blooms, either the following combinations: dark blend, variegated and bicolour.

Also, research suggests that they are very genetically volatile – Even growing conditions may lead to a change in colour.

Bicoloured Dahlias is often a randomly occurring abnormality and may not reoccur the following year – the flower may favour one of its two colours when it grows again.

Did you know?

Within the 20,000 cultivars of dahlias, you won’t find a true blue. It has been attempted many times but with no success. You also won’t find a truly black dahlia flower, and any that appear to be, are either dark red or dark purple.

Red dahlia
White dahlia
Orange dahlia
Yellow dahlia
Pink dahlia
Purple dahlia
Bicolour dahlia
'Black' Dahlia

Do Dahlias flower in the first year?

Dahlias will flower in the first year.

This can be as early as 8 weeks after planting, depending on the weather and whether you are growing from tubers or seeds. They are typically very successful bloomers.

Do they need staking?

It depends on the variety. Dwarf bedding Dahlias do not need staking.

Dahlias that are top-heavy and tall will need stout posts for support, one per stem. Dahlias with multi-petalled blooms are likely to be in this category.

Dahlias with smaller blooms will still likely be top-heavy and need support as they grow. Bamboo canes should be sufficient.

Do Dahlias need deadheading?

By deadheading your Dahlias regularly, they are more likely to reflower. You can do this as often as weekly – this will ensure the plant puts its energy into flower production.

When deadheading, cut above the first pair of leaves you find below the flowerhead.

What do you plant with Dahlias?

Companion dahlia cosmos


A classic pairing, particularly if you choose single-flowering Dahlias – both are great for a pollinator-friendly space.

Companion dahlia verbena bonariensis

Verbena bonariensis

They have loose stems that complement Dahlias without creating over-dense planting.

Companion dahlia achillea


These have similar growing conditions and are quite tolerant.

When do they die back?

Once the first frosts of the year start. This is typically in late autumn, likely in late November.

When to cut down Dahlias?

This should be done in the autumn once the foliage has been blackened by the first frosts. Cut the stems to approximately 10-15cm from the ground.

If you live in a milder region, and have well-draining soil, the tubers can be left in the ground with a deep layer of bark or mulch to protect them from the frosts.

When is the best time to take my over-wintered Dahlias outdoors?

First you need to water them, pot them up, and then they wil be ready to plant out outdoors in May, after the frost risk has passed.

Can you divide Dahlias?

Yes, gladioli is poisonous to dogs and cats. Try growing them in containers that are out of reach if your pet is likely to try to nibble on your gladioli plants.

Eating the plant itself may cause vomiting, stomach upsets, and lethargy if consumed by dogs. But it is the corm you want to ensure they don’t try to eat, as this is the most toxic part.

Dividing dahlia tubers

How do you divide Dahlias?

To divide your Dahlias, lift the tuber using a garden fork or spade, and divide using either your spade or a pair of secateurs.

It is then up to you whether you plant them again straight away, or if you store them to plant the following year.

Will Dahlias spread?

This is unlikely. Dahlias do not self-seed easily, and unless you divide the tubers, they will only grow one plant per original tuber.

Sometimes these tubers will divide on their own, but if you want to multiply your yield the best bet is to divide them yourself.

Otherwise, dig up your tubers and divide them, but don’t replant the ones you don’t want. Perhaps gift any unwanted tubers to an avid gardening friend or family member?

What are the common problems with Dahlias, and how do you fix them?

If your Dahlia is producing too much foliage and not enough or any blooms, you may not have planted it in a sunny enough position. Dahlias should get at least 6 hours of sunlight per day, otherwise, they will ‘stretch’ towards whatever light is available.

Or the temperature of the soil may be a little too cold. You may also be giving your Dahlias too much nitrogen than other nutrients like phosphorus or potassium. This would encourage more foliage growth than blooms.

Sunny spot for dahlias

Why won’t my Dahlia buds open?

If your buds won’t open, your plant may have insect damage. Otherwise, this may be caused by too much or not enough water, so check the soil and treat your Dahlia accordingly.

Why is my Dahlia leggy and tall?

If your Dahlia is getting quite leggy and tall, it may be that it is not receiving enough sunlight.

What are the common diseases of Dahlia?

There are three to keep on top of: powdery mildew, botrytis and verticillium wilt.

Powdery mildew dahlia

Powdery Mildew

Powdery mildew can be avoided if you water the base of the plant and try to keep the leaves dry. Pick off any affected foliage.

Dahlia botrytis


Botrytis, otherwise known as grey mould, is encouraged by cloudy and wet weather. Remove affected leaves as soon as you spot them, as botrytis can spread to the stems and kill the plant.

Verticillium wilt

Verticillium Wilt

Verticillium wilt is caused by a soil-borne fungus. There is no method to fix this, and the plant will eventually die. This can live in the soil for many years, so be careful not to spread soil from the affected area, and perhaps allow the area to grass over for at least 15 years. You can also water heavily and apply nitrogenous fertilisers, but this won’t guarantee that you won’t have re-infection.

What are the common pests for Dahlias?

Slug on dahlia

Slugs and snails

You can try to avoid this by leaving the soil surface as dry as possible or adding organic deterrents like used coffee grounds or eggshells to the surface of the soil.

You can also plant slug/snail-resistant plants nearby, like foxgloves, mint, and lavender.

Another option is to patrol your garden daily in either the morning or evening of damp days and pick the slugs and snails off your garden.

Earwig dahlia


To deter earwigs, remove any spent flowers, foliage, and organic matter.

Earwigs are a great beneficial bug to control fruit aphids on trees, so tolerate them if you can.

When mulching your Dahlia, avoid using shredded leaves or straw material, as this is a great environment for earwigs.

Thrips on leaf


On Dahlias, expect these to be onion thrips. You may find foliage silvering, stunted growth, and distorted leaves.

Tolerate as much damage as you can, but you could encourage natural predators such as Orius laevigatus into your garden.

Are Dahlias poisonous to humans?

Dahlias flowers and tubers are edible to humans; they are not poisonous. They tubers have been eaten since the Aztecs of South America.

They are high in Inulin, which is good for the bacteria in your gut. It is also a low-calorie carbohydrate.

Anders Dahl, a Swedish botanist, categorised dahlias as a vegetable originally! They are rumoured to taste like a combination of potatoes and radishes.

Are Dahlias poisonous to pets?

Dahlias are not safe for pets.

There is a toxic substance in them that causes skin irritation, and tummy upsets in dogs.

Dahlias are colourful, striking plants to enjoy in your garden. If you have any questions about this or any other plants you want me to do a video on, please subscribe to my YouTube channel and leave a comment below one of my Google Questions videos.

Find out my answers to Google’s most asked questions about Gladioli:

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