Summer wouldn’t be summer without dahlias. Their beautiful flowers come in almost every colour imaginable, from pale pastels to hot, vibrant shades. They come in a range of flower shapes, from small tight balls to lily-like blooms the size of dinner plates. They’re perfect for adding late summer colour to borders from July to October and look good in any style of garden, from a cottage-style border to a jungle or exotic scheme. They look especially good with cosmos, grasses, Verbena bonariensis or cannas.
Dahlias come in a range of different sizes. The dwarf varieties can be grown as bedding, while more compact varieties grow very well in pots, while . Tree dahlias (Dahlia imperialis), from which all modern dahlias were bred, can reach 5m tall.
Dahlias make brilliant and prolific cut flowers – the more you cut them, the more flowers they produce. Because of their complex flowers, most dahlias are not attractive to pollinators. So be sure to include some single-flowered varieties if you can – these are popular with bees and butterflies.
Dahlias hail from central America – they were brought to Europe by the Spanish, along with potatoes and tomatoes, initially for eating. They like plenty of sunshine to thrive and are tender – they need protection in winter.
You can buy dahlia plants at the garden centre in summer, but many gardeners grow them from tubers. These are potted up and brought into growth indoors in late March or early April, then planted out in the garden in May once no more frost is forecast. Dahlias can also be grown from rooted cuttings and from seed.
Gardeners in colder areas tend to dig up their dahlia tubers once the first frosts arrive in autumn, then bring them indoors over winter.
How to grow dahlias
Dahlias require a fertile, moist but well-drained soil, and a sunny, sheltered spot. The taller varieties need staking. In autumn, dig up the tubers and overwinter them in a frost-free place, such as a greenhouse or a shed. Bring them back into growth in early April, then plant out in the garden from May onwards.
More on growing dahlias:
Dahlias: jump links
- Where to grow dahlias
- Growing dahlias from tubers
- How to care for dahlias
- Overwintering dahlias
- How to propagate dahlias
- Dahlia problem-solving
- Types of dahlia to grow
- Dahlias by colour
Where to grow dahlias
Dahlias like a sheltered spot, with as much sun as possible – a south or west facing border is ideal. Dahlias are not fussy when it comes to soil. For best results grow in any fertile, moist but well-drained soil. Enrich the soil with some organic matter, such as well rotted manure. If you’re growing on heavy clay, add some grit to the planting hole. If you’re growing dahlias in pots, use a good quality, peat-free multi-purpose compost.
Growing dahlias from tubers
Dahlia tubers are available to buy from February. Most garden centres have a good selection but for the best range, buy online.
In early April, you can put all of your tubers in a large, shallow tray, lightly covered with compost, for potting up a little later. Alternatively, pot each tuber up individually, in a large plastic pot filled with multi-purpose potting compost. Position the tuber the right way up (look for the old stem, or a new shoot – this is the top) and position it so that it sits just below the soil surface. Water in well, allowing any excess water to drain away.
Put the tubers in a light, frost-free place (such as a greenhouse, cold frame, porch or windowsill) and keep the compost moist. New shoots should start to form about five weeks after planting. They will have formed bushy plants by the time the frosts have ended in May.
Watch Alan Titchmarsh demonstrate how to plant dahlia tubers, in our No Fuss video guide:
How to plant dahlias
In mid to late May, once no more frosts are forecast, dahlias can be planted out into the garden. Before you do this, you may need to remove some shoots from the tuber, leaving around five remaining. It feels harsh, but it will encourage bushy plants that will produce lots of flowers. You can use any extra shoots to make basal cuttings – see below.
Harden off the plants (acclimatise them to the outdoors) before planting your dahlias outside – put them outside during the day but bring them back inside at night for a week or so.
Dig a planting hole that’s around 30cm across, and add a bucket full of well-rotted organic matter to increase soil fertility. If your soil is heavy clay, you could add some horticultural grit to the base of the planting hole, for drainage. Protect the new shoots from slugs and snails. If you’re planting a dahlia bought at the garden centre, plant at the same depth they were in the pot.
Dahlias like plenty of room to grow – grow them around 60cm apart.
Once you’ve planted your dahlia, you will need to provide it with some support, unless its a dwarf variety. Dahlias grow fast and have a tendency to flop, especially if the flower heads are large. Add a stout stake or bamboo canes at all four corners (these will be hidden as the plant grows). Tie the new growth in every couple of weeks.
If you’re planting dahlias in a pot, choose a large container that’s at least 30cm wide and deep, and fill with multipurpose compost, mixed with organic matter such as well rotted manure. You could add some slow-release plant food at the same time. Plant at the same depth as they were in their original pot.
How to care for dahlias
Once the plant has reached about 20cm tall, encourage more flowering side shoots by pinching out the main growing tip. Remove the main shoot (in the centre of the plant, growing upright) down to the top pair of leaves, using a sharp knife or your thumb and forefinger.
Tie in new growth to the stake every week or so.
Once a fortnight, feed your dahlias with a high potash feed, such as tomato feed. This keeps the flowers coming. Water well once a week.
Deadheading dahlias is very important to prolong flowering. The difference between buds and spent flower heads can be confusing – the buds are round, while spent flower heads are more pointed. Remove the whole flowering stem. Here, Monty explains how to deadhead dahlias:
If you’re growing dahlias for cutting, cut the flowers when they are fully open.
Here, dahlia expert Michael Mann reveals his three Golden Rules of caring for dahlias:
In many parts of the country, dahlias will not survive if left in the garden over winter if it is very frosty or wet. It is therefore best to lift the tubers once the foliage has been blackened by frost. Cut the stems back to about 12cm, then, with a garden folk, gently lift the tuber and remove the soil with your fingers. Place tubers upside down in a newspaper-lined tray so that they can dry out for a couple of weeks in a dry place.
Once dry, place the tubers in a cool, frost-free place in a shallow tray of dry compost or horticultural sand. Don’t water them. They don’t need light during this time, making a dark garage the perfect store. Leave them here until it’s time to pot them up again, in late March or early spring.
If you live in a mild area with well drained soil, or don’t have the space to lift and store dahlia tubers, you can cover the soil with a thick layer of mushroom compost and/straw, to prevent frost from penetrating the tubers. In spring simply rake away the excess compost.
Here, Alan Titchmarsh demonstrates how to lift dahlias for winter:
Dahlia tubers of a good size can be divided in spring. To do this, press the tubers down onto a tray of shallow compost and leave them to start growth in a greenhouse or in a sunny room. Keep the compost warm and moist. Once the tubers start to produce shoots, divide them using a clean, sharp knife so that each section has at least one shoot and set of roots. Pot on the divisions and grow on to plant out once all danger of frost has passed.
Dahlias can also be easily propagated by taking basal cuttings in spring. Each tuber will give you around five new plants for free that will flower in summer. You can also buy rooted cuttings online in spring. These will produce small plants in their first year, so will be more suitable for pots, but they will flower well.
It’s also possible to grow dahlias from seed.
Growing dahlias: problem solving
Dahlias are prone to attack from earwigs. They’ll eat their foliage, buds and flowers. Create earwigs traps by pushing a garden cane into the soil and placing an upturned garden pot stuffed with straw on top of it. During the day the earwigs will retreat to the pot and you can then dispose of them.
Slugs and snails adore dahlias, especially the new growth. Planting out plants when they are a decent size helps; as does surrounding the plant with a copper ring. You can also scatter organic slug pellets, which do not harm wildlife. Read our guide to protecting young plants from slugs.
Capsid bugs can also be a problem. Find out how to stop capsid bugs eating your dahlias, in our Quick Tips video:
Advice for buying dahlias
Here’s our advice for buying dahlias from the right type for your garden, and where to buy online.
- Bear in mind that dahlias come in different sizes – some are dwarf types, suitable for bedding displays, others are medium-sized and good for pots, while some are large and better suited to a large border or cutting patch. So check the plant’s ultimate size before you buy.
- Check that you have the right conditions to grow dahlias – they like a sheltered, sunny spot.
- If you’re buying tubers at the garden centre, check that they are large and plump, with no signs of rot or mould.
Where to buy dahlias online
Types of dahlia to grow
Single dahlias such as ‘Joe Swift’ and ‘Bishop of Llandaff’ have a single ring of petals that circle around a central disc. This type of dahlia is attractive to pollinators.
Cactus dahlias such as ‘Doris Day’ and ‘Ryecroft Pixie’ have fully double blooms, with very narrow petals from the tip to the base, that curve outwards. They range in size from miniature to giant.
Semi-cactus dahlias such as ‘Dame Deirdre’, ‘Pink Preference’ and ‘Vulcan’ have fully double, fluffy-looking flowers. The petals have a broader base at the bottom than cactus dahlias and are rolled for about half of their length.
Pompon dahlias such as ‘Moor Place’ and ‘Franz Kafka’ are perfect spheres, formed of petals that are curved inwards. Their flowers are smaller than those of ball dahlias, below.
Ball dahlias including ‘Jomanda’ and ‘Aurora’s Kiss’ are larger than pompon dahlias and have a spiral arrangement of curved petals that form a ball or a slightly flattened sphere.
Waterlily dahlias including ‘Kilburn Rose’ and ‘Taratahi Ruby’ resemble waterlily flowers – they have broad, shallow double flowers that are shaped like a saucer, with curved or flat petals.
Anemone dahlias such as ‘Lambada’, have an unusual look – they have tubular florets in their centre, surrounded by at least one ring of flatter petals on the outside.
Decorative dahlias such as ‘Checkers’ and ‘David Howard’, have fully double, slightly flat and broad petals, often with a blunt end, and no central disc. They’re the largest of all the dahlias – flowers can be up to 25cm in diameter.
Collarette dahlias have large petals that surround a ‘collar’ of smaller petals around a central disc. They include ‘Chimborazo’ and ‘Yankee Doodle Dandy’.