Dahlias care and growing guide: top tips for stunning blooms
These tips on how to grow dahlias will help you bring bold and beautiful colors to your summer borders, flower beds and containers
If you're wondering how to grow dahlias, then you've come to the right place. After falling out of fashion for a while, these beautiful blooms have staged a big comeback and their newfound popularity shows no sign of waning. After all, these incredibly varied plants offer something for everyone.
Dahlias are totally versatile, too – you can plant them in borders, grow compact cultivars in containers, or treat them as a cutting-flower crop for show-stopping displays indoors. And, they can also be very good value for money – a single dahlia tuber can produce blooms from the middle of summer right through to the first frosts.
Whether you want to fill your flower beds or just test out one or two varieties of these stunning blooms in pots, they're a fail-safe option for gardens big and small.
'Anyone who grows dahlias will know they start flowering in mid-summer but are at their best during late summer and fall, delivering masses of blooms right up until the first frosts,' says Amateur Gardening's Anne Swithinbank. 'Originally from the uplands of Mexico and the narrow strip of countries where North and South America connect, these equatorial plants enjoy plenty of sun, cool weather and hit peak performance when the hours of night and day are similar. Plant dahlias and you will have a brilliant late show in the garden and masses of blooms for cutting.'
How to recognize dahlias
Dahlias are our most flamboyant summer flowers. Their blooms vary in size from small single flowers shaped like daisies to dinner plate dahlias with fully double flowers 12in (30cm) across.
Strong growing, fleshy shoots grow from dahlia bulbs (technically tubers) shaped like a collection of very fat fingers connected at one end – where the shoots develop. Hollow stems carry bold divided foliage which is usually dark green but which, in some of the most useful garden varieties, is heavily bronzed. From early summer the fat buds burst into bloom and the flowers can keep coming until the first frost of fall.
They're outstanding in a sunny border, superb – and very fashionable – as cutting garden flowers, and dwarf types are ideal for patio containers.
Dahlias are classified into 17 different groups – yes, 17! – mainly on the shape of their flowers. Most groups are then again divided by flower size.
At one end of the scale are the Single types of dahlias with each flower made up of a ring of petals around a bold golden eye. Usually less than 4in (10cm) across, Single dahlias come in a good range of rich and pastel colors, have a natural simplicity and are popular with pollinators.
At the other extreme, Decorative dahlias have fully double flowers with no eye visible. There may be hundreds of petals in one flower, each one flat, or slightly turned in at the edges, and in a fantastic range of flower colors. The flowers vary in size from less than 4in (10cm) to over 10in (25cm).
How to plant dahlias
Dahlias, which grow fresh from tubers every year, aren’t very good at pushing up through herbaceous plants. So, if you're growing them in a garden border, it's best to give them their own bit of space.
'Planting tubers around 4-5in (10-12cm) deep in prepared ground during mid-spring is the most straightforward method,' says Anne Swithinbank. 'Remember though that dahlias dislike crowding and need space to develop. If you want earlier flowers, plant tubers in pots under glass in early spring for planting after danger of frost.'
Garden expert Tamsin Hope Thomson for Amateur Gardening shares her top tips for planting dahlia tubers:
- Pick a spot that gets plenty of sun (especially important if you want to leave the tubers in the ground over winter), with well-draining soil.
- Dig a square hole around 12in (30cm) wide and deep, and space out your tubers about 24in (60cm) apart.
- Then, fill it back up with compost. Keep the compost on the dry side until signs of growth appear, then water more frequently.
- The most successful dahlias also have a good supply of well-rotted manure placed around the base soon after planting. Whether you've done this or not, the plants should also be fed every few weeks throughout the growing season. Alternate between a seaweed tonic and a potash-rich tomato feed.
How to grow dahlias in pots
Dahlias are great for container gardening ideas. Those specially developed for pots, including the Happy Single Series, are particularly effective. Start off your dahlia bulbs in small pots, grow them on and then use them as the centerpiece for large containers (even up to 2ft/60cm across). Treat dahlias bought in flower in the same way.
Use moist, fresh container planting mix, set your dahlia in the center first, then plant bushier summer flowers around the edge. They not only will provide contrast or harmony in color but will also hide the base of the dahlia where the leaves sometimes die off.
Growing dahlias from seed
'Growing dahlias from seed is a great way of enjoying plenty of plants cheaply and easily,' says Anne Swithinbank.
'To grow flowers from seed, sow seeds thinly and evenly in spring, cover very lightly with compost or vermiculite and germinate at 65˚F (18˚C). Transplant seedlings singly to pots, grow on, and plant outdoors in late spring or early summer. Go for something like "Bishop’s Children", which delivers a pleasing mixture of single flowers against dark foliage, plus you can save the tubers of favorite colors.'
When should you plant dahlias?
Dahlias are tender plants, so it's important to keep them protected from frosts. Because of this, it's generally best to start tubers off undercover in your greenhouse, or even a DIY cold frame in early or mid-spring. Then plant them out once the temperatures outdoors are reliably warmer – generally around late spring to early summer.
Remember to harden them off before planting, by standing the pots outside in the garden for a week or two so they can gradually acclimatize to the outdoor conditions.
Dahlias care tips
The beauty of dahlias is that they're not overly demanding, so can be added to your plot as part of your low maintenance garden ideas. However, they do require the right care at the right time to keep them happy.
During the summer and early fall months, your dahlias care routine should include watering them regularly throughout dry spells. Remember to feed them, too.
Don't be afraid to cut flowers off for displaying indoors because this will actually help your dahlias. Regular picking encourages them to keep on producing flowers – what a win! Deadheading dahlias regularly is also advised, plus make sure you check for pests and signs of other diseases.
Staking dahlias for added support as they grow
Some dahlias are taller than others, which means they'll need a little more support to stop them from toppling over. It's worth knowing these tips:
- Dahlias can be very brittle at their base, meaning whole stems are easily broken if it's windy.
- Ideally, plants should be staked at the time of planting in late spring to early summer.
- Use bamboo canes to support the plants and tie the stems with twine at 12in (30cm) intervals. If you haven't done this already, make sure you do so as soon as possible, as your dahlias get taller.
- Be careful not to damage the roots as you insert the canes, and make sure they are as close to the plant base as possible.
- Larger plants may need several stakes. Continue to tie in the stems as the plants grow taller for added support.
Taking cuttings from dahlias
As with all flowers, taking cuttings from plants is a fantastic way to get new plants for free. Gardening expert Ruth Hayes of Amateur Gardening shares her step-by-step tips for taking cuttings from dahlias.
- Mix seed compost with perlite in a 4in clay pot, then add a little water to dampen it.
- Using a clean knife or your best secateurs, remove just a few strong shoots from your dahlia plant, each at about 4in (10cm) in length.
- Remove the lower leaves, otherwise they may rot when you pot your cuttings up.
- Dip the ends of your cuttings in rooting compound – this will help to promote strong and healthy root growth.
- Insert the cuttings into the compost and perlite mix and carefully firm them in.
- Seal the newly potted cuttings in a plastic bag and place somewhere light and warm – such as in your greenhouse or on a sunny windowsill. New roots will soon begin to develop.
How do you get bigger blooms on your dahlias?
To get good, long dahlia stems and larger (but fewer) flowers, cut off all side growths 24in (60cm) below the growing tip. This allows plenty of stem for cutting, if you want to arrange them in vases indoors. And, it also allows lower shoots to go on growing to produce replacement stems.
Another tip to ensure show-stopping blooms is to retain just the top bud and pinch out all the other flower buds immediately below.
What should you do with dahlias in winter?
'In colder regions and for ease of management, it is best to lift tubers after foliage has been blackened by the first frosts,' says Anne Swithinbank. 'Dry and store them frost-free, covered by slightly moistened old compost or sand.'
If you're in a warmer part of the world, you don't have to lift the tubers. 'In milder regions, dahlias can withstand most winters in the ground under a dry mulch of leaves or bark,' explains Anne Swithinbank. 'However, they might be late into flower and sometimes large, old tubers lose vigor.'
If you're going to leave tubers in the ground, the best method is to simply cut back the plants and then apply a layer of mulch or compost to the crowns for extra insulation. Our guide to mulching has more info should you need it.
Problems to look out for with dahlias
As with most plants, a few problems can arise. Here are some to look out for:
- Dahlias can be prone to pests including snails and aphids, so check them regularly for signs of infestations. Pick off snails or catch them in beer traps. You can use chemicals to get rid of aphids, but a more environmentally-friendly option is to introduce natural predators such as ladybirds and hoverflies. Our guide on how to get rid of aphids is full of useful advice.
- Earwigs can also be a pest to watch out for when growing dahlias. You can collect them in simple paper traps. Crumple up newspaper and place in an upturned flower pot that can sit on top of your stakes. This attracts the earwigs and keeps them off the plants.
- Diseases such as powdery mildew can be a problem for dahlias. You can improve your chances of prevention by removing dead and damaged foliage before it starts rotting and by creating good airﬂow around plants.
Are dahlias deer resistant?
No, dahlias are not deer-resistant plants. They're not the favorite deer food, but if deer come across your dahlias they will probably eat them.
If you have deer in your area the best way to protect your dahlias is to install a fence. This will protect your whole yard and allow you to grow whatever you like – with no trouble from the deer at all.
Spray-on deer deterrents can work, but repeated application is necessary to maintain the protection and summer thunderstorms can wash the treatment off and leave your dahlias vulnerable.
Is there such a thing as a black dahlia?
Black plants always make a statement in a garden. There are some dahlia varieties with flowers that can seem black – but look closely and you will usually see that they are, in fact, very very dark maroon.
‘Karma Choc’, and the smaller flowered ‘Arabian Knight’, are favorites in this color, and listed by many dahlia suppliers. ‘Black Beauty’ is also worth looking for and, although it has a big golden eye, the ring of petals around it is as close to black as you can get.
How to buy dahlias
There are a few different ways to buy dahlias. The easiest is to start with dahlia tubers, which can be bought individually, packed in plastic bags at garden centers and other retail outlets.
A far wider range of tubers is available by mail order from bulb specialists and from dahlia specialists as well as from nurseries offering a general range. The best plan is to order in summer and fall, for delivery in spring. Suppliers will usually time the shipping of your dahlia bulbs in line with planting time in your area.
Dahlias can be grown from seed, although the results are unpredictable, and dahlias are also sold in large pots, in flower, in some retail outlets.
Some mail-order suppliers also sell rooted dahlia cuttings, for growing on in a frost-free place before planting out after the last frost. Young dahlia plants are also offered by some suppliers, these are garden-ready and should be delivered around planting time.
Where to buy dahlias
If you want to add some of these fabulous flowers to your own backyard, our quicklinks below will help you start your search.
Where to buy dahlias in the US:
- Buy dahlias at Walmart
- Buy dahlias at Amazon
- Buy dahlias at Lowes
- Buy dahlias at Summer Dreams Farm
- Buy dahlias at Golden Rod Gardens
- Buy dahlias at Triple Wren Farms
Where to buy dahlias in the UK:
Teresa has worked as an Editor on a number of gardening magazines for three years now. So she is lucky enough to see and write about gardening across all sizes, budgets and abilities. She recently moved into her first home and the garden is a real project! Currently she is relishing planning her own design and planting schemes. What she is most passionate about when it comes to gardening are the positive effects it has on our mental health to grow and care for plants, as well as being great for the environment too and help provide food and shelter for wildlife.
- Graham RiceFreelance writer
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