how to plant, grow & care for dahlias

complete growing guide

Dahlias are some of the lowest maintenance, highest production cut flowers and garden plants you can grow. Here at Perch Hill, we grow hundreds and hundreds of dahlias, and they are the highlight of the summer and autumn garden. Excellent cut for a vase, each dahlia tuber can produce hundreds of flowers, meaning a colourful show inside and out for weeks on end. They come in all different sizes and colours, each as exciting as the next, but they also come in myriad shapes. Find out more about dahlias by exploring our huge collection of dahlia plants and tubers.

details

  • Common name: Dahlia
  • Latin name: Dahlia
  • Type: Tender Perennial Tuber
  • Height: Compact dahlia varieties reach about 40cm (15in), others can reach over 1.5m (5ft)
  • TLC rating: Easy
  • Aspect: Full Sun
  • Planting position: Borders, Containers
  • Suitable for pots: Yes
  • Good for pollinators: Yes, the single types (rather than doubles) are good for pollinators
  • Good for cut flowers: Yes

calendar

JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
Sow Under Cover/Plant Indoors
Direct Sow/Plant Outdoors
Flowers/Harvest

how to grow dahlias

where to grow dahlias

Soil type: Dahlias grow best in a fertile, well-drained soil.


Aspect & position: Dahlias thrive in most sunny situations, but a sheltered position is ideal.


when to plant dahlias

Dahlias are tender tubers, which means they won’t survive a frost. Start them off undercover in early spring, then plant them outside after the frosts have passed in late May or June.


how to plant dahlias

sowing dahlia seeds

Dahlias are commonly started into growth as tubers, as this is a faster and often more reliable way to grow them, but it is possible to grow dahlias from seed.


Dahlia seeds should be sown between February and April undercover. Sow 0.5cm deep in trays of moist compost. Place in a warm position, about 15-20°C (60-68°F). Keep moist. 


Transplant seedlings to deeper trays or individual small pots when large enough to handle. 


Grow on in cooler, but frost-free conditions. Gradually harden off young plants before planting out after the risk of frost has passed in May and June.

planting dahlia tubers in pots

Dahlia tubers can be started into growth in March or April in pots undercover, and then planted out in the garden in late May and June. 

Start by half-filling a 2 or 3 litre pot with peat-free multipurpose compost. Place the tuber in the pot with the central stem upwards and cover with more compost. Don’t forget to label and lightly water the pot, then place it somewhere warm and frost-free – a greenhouse is ideal. Don’t water again until they start to shoot, and even then only water lightly.

After 2-3 weeks, shoots will start appearing – some varieties may take a little longer. As these shoots grow, pinch out the tips of the main shoot (you can use a sharp knife or a squeeze between your thumb and forefinger), down to the top pair of leaves.

As the plant starts to grow further, remove all but five shoots sprouting from the tuber. This will feel harsh, but by having only five stems, this will allow each stem to develop, grow strong and vigorous, and the result is lots of flowers!

Watch a video on how to do this below.

planting dahlia tubers in the ground

If you don’t have space to plant the tubers in pots first, you can put them straight into the ground in spring – just make sure the frosts are nearly over. 

Plant the tubers just under the soil surface and ensure they are approximately 75cm (30in) apart, depending on variety. 

Insert a stout stick to act as a stake when planting as they can make sizeable plants when fully grown. Mulch over the top of them or protect them with a cloche or horticultural fleece. This is particularly important if the foliage appears before the frosts are over.

Whether you have raised your dahlia tubers outside in the garden or undercover, you need to pinch out the tips of the main shoot once three pairs of leaves have grown. You can use a sharp knife or a squeeze between your thumb and forefinger, and pinch out down to the top pair of leaves.


planting dahlia plants 

If you have a dahlia in a 2 or 3 litre pot that you’ve grown from a tuber or bought as a plant, you can plant it outside once the risk of frost has passed in spring. Dig a planting hole for each plant in a sunny, sheltered position.
 
The hole needs to be at least 30cm (1ft) square, 30cm (1ft) deep and the plants should be spaced approximately 75cm (30in) apart, depending on variety. Add plenty of organic matter to the hole. On heavy clay, add grit to the planting hole. Place the dahlia in the hole with the tubers just below the soil surface and fill in around the rootball.

Insert a stake when planting as they can make sizeable plants when fully grown. You will need a stout stake (not just a bamboo cane) to support each plant and it is a good idea to knock this in first and then place the plant by its side.

As they grow, pinch out the growing tips once three pairs of leaves have grown to encourage branching. 

With the stake in place at planting, you can continue to tie them in every couple of weeks. Dahlias grow very quickly once they get going and can easily break off right at the base in wind or rain if they are not securely staked.

growing dahlias in a pot

Dahlias are usually started in pots undercover and then planted out in the garden, however it is possible to grow dahlias in a pot. Make sure you choose a slightly compact dahlia variety, as some dahlias can grow over 1.5m (5ft) tall. Then choose a container which is at least 30cm (1ft) in diameter and 40cm (15in) deep for optimum growth. Use peat free multi-purpose compost and add a slow-release fertiliser for strong growth.

Plant dahlia tubers and plants as you would when planting in the ground, just under the surface of the compost. Then add a stake, a label and water well.

If you’re starting dahlias into growth in March or April, place the pot somewhere light, warm and frost-free. If you’re starting in early summer, simply leave the pot outdoors.


how to care for dahlias

watering

Dahlias prefer a moist soil. In a drought, water them once a week and water with a good flood, not a gentle sprinkle. If your dahlias are in pots, water them frequently – every day during a drought. They are thirsty plants.

fertilising

If your dahlias are in pots, either use a slow release fertiliser or feed fortnightly with a liquid comfrey or seaweed fertiliser. Start after the first month.

staking

All dahlias should be grown alongside a stake. Make sure to continue to tie the dahlias in every couple of weeks. Dahlias grow very quickly once they get going and can easily break off right at the base in wind or rain if they are not securely staked.

deadheading

If you don’t pick every dahlia flower for the house, they will need regular deadheading, which will promote flowering. To deadhead, follow the flower stem down and cut above the first pair of leaves you meet.

propagating

Dahlias are easily propagated from basal cuttings. In the spring, once the tuber has started sprouting, select strong, healthy shoots about 7.5cm (3in) long. Remove them with a clean, sharp knife along with a small portion of the parent tuber.
 
Remove all but the top pair of leaves and pinch out the tip.

Prepare a 1 litre pot with a mix of compost and grit (3 parts compost to 1 part grit). Place each cutting at the edge of the pot, with the leaves just above the top of the compost and spaced so that they are not touching.
 
Water from above to settle the compost. Then place somewhere light, but out of direct sunlight in a warm spot or in a heated propagator. Label the pot.

In about 3-4 weeks the cuttings will have formed roots, carefully pot each cutting individually into a 7.5cm (3in) pot and grow on, planting out after the risk of frosts has passed.
 
With regular feeding and watering, the plants grown from cuttings will flower later the same summer and form tubers.

overwintering

There are two ways of overwintering dahlias. 

overwintering in the ground

In recent years, our winters in the south of England have been so mild that dahlias left in the ground, mulched deeply to protect them from the frost, have re-emerged fine, bulking up and flowering well before the other plants grown in pots. You could opt for this low-maintenance regime, but you risk losing your plants if we are hit by a hard winter.

If you go for this option, dahlias can be left in place and protected with a thick mulch on top over, which you can clear away once the worst of the frosts are over in the spring.
 
To do this, wait for the dahlias to get blackened by the first frosts of autumn, then cut them to within 10cm (4in) of the ground. Then put labels where the crown is showing – make sure each dahlia is labelled, as it’s so easy to forget which plant is where. Then add a mound (a whole bucket) of mulch over each one – if you bury them deep, it’s like giving them a duvet for the winter.

overwintering by lifting

The second way is to lift the dahlias out of the ground and store them undercover. This lifting method is advised if you’re growing dahlias in a mixed border, as dahlias left in mixed beds could become overshadowed by spring and summer growth.

To be sure of conserving your plants for next year, dig them up after the tops have been frosted in the autumn. Cut them down to 15cm (6in) before you do so. Knock off the surplus soil and, with a small piece of stick, scoop out the loose soil between the tubers – but leave enough to hold them in place.
 
Do not clean the tubers under a tap; to get water on a tuber at this time of year often spells disaster. Turn the tubers upside down in a crate and leave to dry for a couple of weeks. 

Then pack them away in shallow trays or in a storage box, surrounding the tubers with dry compost, vermiculite or dry sand, or alternatively wrap them in newspaper. This prevents the tubers drying out.
 
Store them in a cool, frost-free place – a cellar, attic or shed is perfect. Inspect tubers regularly during winter for rotting.

seasonal checklist

spring

  • In early spring, plant your tubers undercover. In late spring, you may be able to plant tubers directly outdoors. Remember to stake each plant

summer

  • Dahlias should all be planted out by early summer and the fast-growing varieties will be in flower by July.


autumn

  • Enjoy a glorious show in the garden, with plenty of flowers to cut and bring indoors. The dahlias will continue to flower into November. Remember to deadhead to keep the dahlias looking their best.

winter

  • Ensure your dahlias are protected from frost by overwintering them either in the ground or by lifting them and storing them indoors.



pests, diseases & common issues

earwigs

Earwigs can be a problem with dahlias, eating the flowers and the leaves. The organic way of control is to position small pots filled with straw upside down and raised on canes dotted throughout your dahlias. The earwigs crawl into the straw in the heat of the day. At the end of the day you can release them somewhere else far from your dahlias. But don’t just think of them as pests, as they can be beneficial by consuming aphids.

slugs

Slugs also love dahlias, especially when they first shoot, so protect them from the word go. There are a host of options when it comes to protecting dahlias from slugs. Try harmless slug-repellents such as wool pellets, which form a natural barrier to slugs and snails, or copper bands, which slugs and snails hate.

why are my dahlias not blooming?

Underwatering your dahlias is the most common reason for failed blooms. Keep the soil moist and water generously, especially in a drought or if you’re growing them in pots. Make sure they are positioned in full sun, ideally in a sheltered place.

why are my dahlia tubers not sprouting?

A common mistake is to regularly water tubers you have just planted and too much water at this early stage can lead to rot. Water the compost once when you first plant the tuber, then wait until you spot the first sprouts before watering again.

why is my dahlia wilting?

Growing dahlias can be thirsty plants once they are in full growth. Make sure the soil around them is moist, which can mean watering every few days in a drought.

how to stop slugs from eating dahlias?

There are a host of options when it comes to protecting dahlias from slugs. Try harmless slug-repellents such as wool pellets, which form a natural and barrier to slugs and snails, or copper bands, which slugs and snails hate.

why are my dahlias so short?

Some varieties of dahlias are very compact, so check the information on the seed packet of research the variety you have to find out its final size. If the growth is stunted, it could be the conditions the dahlia is in – a cold snap or a late frost can impact growth. Make sure your dahlias are in a sunny spot.


frequently asked questions


how tall do dahlias grow?

There are compact varieties around 40cm (15in) tall, as well as varieties that reach over 1.5m (5ft) – as well as everything in between!


when do dahlias start to sprout?

You’ll see tubers planted in early spring start to sprout 2-3 weeks later.


are dahlias perennial?

Dahlias are tender perennials and the tubers can be killed by frost. See my advice for overwintering to ensure you have strong dahlia plants from the same tubers each year.


are dahlias edible?

If they are grown without chemicals, dahlia petals are edible. I love to sprinkle them over salads!


can dahlias self-seed?

Yes, they can but they won’t be the same as the parent plant. You can get some interesting offspring appearing.


are dahlias poisonous to pets?

Yes, unfortunately dahlias are toxic to cats and dogs.


are dahlias good for bees?

The single dahlias are a fantastic source of forage for bees and other pollinators, providing nectar well into late autumn. 


where do dahlias originate from?

Very little is known about the dahlia before the time of the Aztecs. It is believed that the Aztecs used parts of the dahlia for food and medicine. The mountain regions of Mexico and Guatemala are the birthplace of today's dahlias and they have continued to be grown there.

how to cut & arrange dahlias

I love how dahlias can look bold and beautiful in an arrangement – they look fantastic en masse with their striking shapes and colours, but they are equally good cut as individual stems each placed in a coloured glass bottle or small vase.


Get some inspiration for displaying your dahlias with our flower arranging videos:


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