After years of being dismissed as old fashioned and garish, dahlias are firmly back in fashion. They are a much loved highlight of the late summer garden, and if deadheaded or cut regularly, they will produce hundreds of flowers until after the first frosts.
Dahlias come in almost every colour imaginable, from cool whites and pale pinks to hotter yellows, oranges and red, to deep magenta and almost black.
Their flower shapes vary greatly, too, ranging from spiky cactus blooms to decorative dahlias, lily-flowered types and the intricate ball and pompon types. The single flowered and anemone types are brilliant for pollinators.
Dahlias combine brilliantly with other late summer flowers such as cannas and ginger lilies for an exotic or jungle look. They also combine very well with ornamental grasses, which peak at around the same time. Dot them through borders or grow them in a dedicated area on a cutting patch or allotment – they make excellent cut flowers. The more compact varieties grow very well in pots.
Don't miss our round up of garden designers' favourite dahlias.
When to plant dahlias
Dahlias are tender, which means they won’t survive a frost. They therefore need to be planted out in the garden in late May or early June, when no more frosts are forecast. If you're growing dahlias from seeds, cuttings or tubers, start growing them in pots in a greenhouse, mini greenhouse or conservatory in early spring, before transplanting them outside in early summer.
How to grow dahlias
You can grow dahlias from tubers, cuttings or seed. All three methods should produce flowers in the same year.
How to grow dahlias from tubers
The traditional way to raise dahlias is from tubers. Order from a dahlia specialist, in January or earlier.
- From the beginning of March, bring dahlia tubers into growth in pots in a greenhouse or polytunnel – they need lots of light and a minimum temperature of 17°C.
- Plant the tubers in large pots of loam-based John Innes No. 2 compost. Keep them moist but not wet. They must be kept warm – even a hint of frost will check growth and blacken foliage. Use thick fleece to protect them on cold nights.
- Once the plant has three to four leaves, pinch the top out to encourage the plant to thicken out.
- Do not plant outside until the first week of June, when the young plants are approx 35cm high. Harden off for at least a week beforehand – this toughens the foliage, helping to deter slugs.
- Dahlias will need support, so stake as you plant.
- Water well in the first half of summer until established. Feed with a potash-rich plant food once buds appear, and deadhead regularly.
How to grow dahlias from cuttings
Commercially-grown, mail order cuttings don’t tend to arrive until May. Alternatively you can take cuttings from tubers earlier in spring.
- Fill 7.5cm plastic pots with John Innes No. 1 compost and water.
- Find new shoots that are 75cm long. Cut just above the base where they join the crown. Discard hollow-stemmed cuttings.
- Trim just below the lowest pair of leaves and remove leaves carefully. Dampen the end and dip into hormone rooting powder. Insert into the pot (several in one pot), making a hole with a dibber. Firm in and label.
- Place in a warm propagator if possible, away from direct sunlight.
- They should root within 20 days. Once new leaves appear, pot up individually into John Innes No. 2. Pinch out the growing tip to make the plants more bushy.
Create this beautiful dahlia combination
How to grow dahlias from seed
Dahlias are surprisingly easy to grow from seed – either from packets of mixes of seeds, or seeds that you've saved from your own plants. You'll need to sow them in early spring, in a greenhouse or heated propagator. The seeds should germinate in a couple of weeks.
- Fill a pot or seed tray with compost, lightly firm the surface and moisten.
- Sow your seeds on to the surface, then cover with a thin layer of compost. Cover with a clear polythene bag or propagator lid.
- Once the ‘true’ leaves appear, transplant into individual pots, holding them by the leaves so as not to damage the delicate stem.
- Pot on as necessary.
- Harden off before planting out in early June.
How to deadhead dahlias
Deadheading dahlias is essential – it keeps them flowering prolifically. A bud and a dead flower can appear remarkably similar, so it can be hard to tell them apart. Dahlia buds tend to be fat, rounded and hard, while the flowered ‘shell’ is pointed and squashy and can be removed.
To deadhead a dahlia, simply remove the deadhead and the thin stem beneath it.
Here's more on deadheading dahlias and more.
Dahlia pests and diseases
Slugs and snails are the main problems you'll encounter with dahlias – the darker leafed dahlias are most prone. Planting out plants when they are at least 35cm high can help, as can watering in the morning as opposed to the evening. Read our advice on preventing slug damage.
Viruses can also effect dahlias, causing the lower leaves to become mottled, but plants usually grow away from the problem.
How to overwinter dahlias
Once dug out at the end of the season, lay the tubers upside down for a couple of weeks in a cool, dry place. This allows moisture to drain out and prevents rotting. Then cover the tubers with sand or sawdust and store in wooden crates over winter. Check regularly for mould.
If you live in a milder part of the UK, you can leave tubers in the ground, covering them with a thick mulch once they have died back in autumn.
Where to buy and see dahlias
Halls of Heddon Tubers and cuttings, plus dahlia fields. West Heddon Nursery Centre, Heddon on the Wall, Newcastle-upon-Tyne NE15 0JS. Tel 01661 852445, www.hallsofheddon.co.uk
National Dahlia Collection 1,700 cultivars from 22 different species of dahlia now lives in over half an acre of garden at the Kehelland Trust in Cornwall, enticing visitors with the huge array of colours on show. The garden is open to visitors from July-October, including some weekends and evenings during the summer months. www.kehellandtrust.co.uk
RHS Garden Wisley Spectacular dahlia trial to view. Woking, Surrey GU23 6QB. Tel 0845 260 9000, www.rhs.org.uk/wisley
Rose Cottage Plants Specialists in mail-order garden tubers. Tel 01992 573775, www.rosecottageplants.co.uk
Halls of HeddonWest Heddon Nursery,Heddon on the Wall,Newcastle upon Tyne NE15 0JS. Tel 01661 852445,hallsofheddon.comJ Parkers16 Hadfield Street, Stretford,Manchester M16 9FG. Tel 0161 848 1100,jparkers.co.ukPeter Nyssen124 Flixton Road, Urmston,Manchester M41 5BG. Tel 0161 747 4000,peternyssen.comSarah Raven1 Woodstock Court, Blenheim Road,Marlborough, Wiltshire SN8 4AN. Tel 0345 092 0283,sarahraven.com