Are you wondering how to grow dahlias? Boasting a huge array of colorful flowers in all sorts of sculptural forms, and in bloom from July right through to the first fall frosts, these showy plants are a brilliant way to bring late-summer color to your garden.
From dainty single and star varieties, to dazzling dinner-plate types with their copious flat petals, dahlias come in a wide range of sizes, colors, and forms making them extremely versatile – there really is a dahlia to suit all gardens and tastes. They can look particularly effective planted en masse or as part of a mixed border, but there are many varieties that will happily grow in containers on a patio, too.
Dahlias are also a brilliant flower for cutting, with stems lasting up to a week in a vase and the more you cut them the more they grow. Plus, they are marvelous multipliers: from a single tuber you could get up to ten 'baby plants' by the end of the growing season.
Read on for our step by step guide on growing dahlias including expert advice on how to plant them and recommended varieties to grow.
What month do you plant dahlias?
You can buy dormant dahlia tubers to plant in spring, or pre-order them earlier from a specialist nursery for delivery in spring. You may even be able to take some from a kind friend who has divided their clump of tubers.
Dormant dahlias will come delivered in the form of tubers – clusters of brown, potato-like roots joined together on a dried stem. All tubers will be different sizes. Ensure that each tuber has some stem and at least one of the buds or ‘eyes’.
Dahlias are frost tender so can only be planted out once the danger of frosts has passed, allowing about eight weeks to the start of flowering.
If you have the space, you are best starting to grow dahlias in the greenhouse or conservatory. 'You can pot them up in March or early April, in a generous pot (at least 2 litres) filled with multi-purpose potting compost. Place them in a light, frost-free place and keep the compost moist. They will have formed bushy plants by the time the frosts have ended and will be in flower by the beginning of July,' advises plantswoman Sarah Raven.
Where is the best place to plant dahlias?
Dahlias will grow best in a sunny spot, protected from strong winds, in rich, moist, well drained loamy soil but not wet, waterlogged soils.
'Dahlias thrive in warm, sunny weather. Plant them in a spot that gets at least six hours of direct sunlight each day. Otherwise your plants will get leggy reaching for the light, and they won't bloom as abundantly as possible,' advises flower farmer and dahlia expert Erin Benzaken, whose new book, Discovering Dahlias (£18.99, Abrams & Chronicle), is released in March.
Prepare the soil well for the hungry plants. Improve it by adding in organic matter, such as home-made compost or well-rotted manure, over the area where you’re planning to grow dahlias.
What is the best way to grow dahlias?
The best way to grow dahlias is to start them off in pots as they are frost tender – by planting the tubers into pots the plants can be kept under cover in a greenhouse or conservatory and protected from the cold weather. Here's our step by step guide on how to grow dahlias in pots from tubers:
Pot up the tubers In April, pot up the tubers into five-litre pots, approx Dia.22cm, filling them up to their necks in potting compost and ensuring that the stem/crown is pointing up.
Place in a sunny, sheltered spot Water the pots and leave them in a sunny spot, undercover in the greenhouse of conservatory. Growth rates will vary but you should see shoots start to appear within five weeks.
Harden off the plants Dahlias should not be planted out until the risk of frost has passed, but as they grow they can be brought outside during the day to help them acclimatise and to give them maximum sunshine. They must be brought in at night.
Pinch out When your dahlia plants are around 30cm tall the growing shoots can be pinched out to encourage a bushier plant and more blooms.
Prepare your bed Dahlias are hungry plants that like being kept moist; digging in plenty of well-rotted manure or organic matter to the soil before planting will keep them well fed and help the ground retain moisture.
Plant out Once the risk of frost has passed, around mid- to late-May, your dahlia plants can be planted out into their flowering position. Spacing will vary depending on variety but generally dahlia plants will need to be spaced around 50cm apart.
Support your dahlias Dahlias can grow up to 1.5m tall so will need support, particularly if you are growing the giant dinner-plate varieties. Once planted, add in bamboo stakes which can be used to tie the plant into as it grows, alternatively you can buy metal support rings that can be placed around the plant.
Dahlia tubers can also be planted directly into the ground once the risk of frost has passed. To do this dig a hole about 30cm deep, add in some compost or manure and wet with a watering can of water. Position the dahlia tubers about 10 to 15 cm deep with the crowns pointing up.
Some dahlias can also be grown from seed which can be done undercover in March and April. Sow the seeds onto the surface of moist compost in a seed tray and cover with vermiculite. Keep in a sunny spot in a greenhouse or on a windowsill. Once seedlings are big enough to handle pot them on into individual pots. Plant out once the risk of frost has passed.
How do you care for dahlias?
Pinch: As the dahlias grow, pinch out the growing tips to promote bushy growth.
Feed, feed, feed: Once a fortnight, between July and September, feed dahlia plants with a liquid balanced feed to boost flowering, such as a good tomato feed.
Water: You will need to water your dahlias once a week in dry weather by giving them a good soaking down to the roots.
Protect: Protect the dahlias from slugs and snails by adding nematodes to the soil, or add barriers, such as rough or sharply textured mulches
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Do you deadhead dahlias?
Dahlias need deadheading regularly, ideally weekly, to keep the plant flowering for as long as possible and well into autumn for late season color and joy. The more flowers you take off, the more they will produce.
It can be tricky knowing spent buds from new – the key is in the shape, new ones are round, spend are usually pointed.
What do you do with dahlias when they've finished flowering?
Dahlias can flower right up to December, but once the frost comes they are over. You can leave dahlia tubers in the ground over winter if they are in a sheltered position with good drainage, but if they are in an exposed site it’s probably best to lift and store the tubers to prevent frost damage.
'I recommend that you wait at least 10 to 14 days after your first hard frost before digging,' says flower farmer Erin Benzaken of Floret Flowers, as this allows the skin on the tubers time to toughen, making them less susceptible to rot.
Knock off as much of the soil as possible, leave them to dry and then wrap in newspaper or in wood shavings and store somewhere frost and damp free. They can then be replanted the following spring.
Can you leave dahlia tubers in the ground over winter?
You can leave dahlia tubers in the ground over winter in mild areas and in very free-draining soil.
After the dahlia flowering season is finished, leave the stems to go black from the first frost for approximately a fortnight to allow the sugars to go back down the stems to feed the tuber. Then cut the stems off just below ground level, mound up the soil or add compost and mulch with straw or bracken to protect the tubers over winter.
How many dahlia varieties are there?
A member of the asteraceae family, there are around 36 species of dahlias, with thousands of various cultivars and hybrids.
Skilled breeders across the world have produced a wide range of dahlia sizes and colors practically unmatched in the world of flowers. Sizes range from the smallest lilliput to dinner plate-sized blooms and there is every color except for that most elusive color for breeders – blue.
Dahlias can be described as:
Select varieties for your weather conditions and by the shape, size and color.
Open–centred single and semi-double varieties that produce an array of simple flowers are the best choice for pollinators as they can see where to land and feed on the nectar, and look charming mingling with asters and other daisy shaped flowers.
Decorative and cacti dahlias are brilliant varieties for a cutting garden, as their 10-15cm blooms are a good size for displaying in a vase. While giant varieties such as Cafe au Lait (pictured below) look show-stopping in a border, their large, dinner-plate blooms are often too large for cutting.
Decorative and cactus dahlias are also the ideal cut-and-come-again flower because they flower for months on end. Picking them regularly encourages more to flower right up to the first frosts. Recut the stems under water and they last in a vase for four to six days.
There are some lovely more diminutive varieties perfect for pots, such as dwarf colarettes, lilyputs and the low-growing Topmix series.
12 of the best dahlia varieties to plant in your garden
(Above left) Bishop of Llandaff started the resurgence of dahlias, the stalwart now of hot borders. This peony-flowered dahlia has vermilion flowers on dark foliage. It dies back in fall, with fresh, new growth in spring.
(Above middle) Moonfire is a low-growing single-flowered variety, ideal for containers or the front of beds. It lights up the garden with its distinctive bi-color blooms contrasting with dark foliage.
(Above right) David Howard is an impressive, decorative dahlia that is lovely in borders with its profuse burnished orange blooms on chocolate foliage. It has more flowers over a longer period than many dahlias, making it one of the most popular.
(Above left) Totally Tangerine, is an anemone type, blending orange and pink tones with outer petals and inner tubular florets. It is great for containers, in borders and as a cut flower.
(Above middle) Honka Surprise is an orchid type with unique star-shaped pink petals and yellow centre. Its compact size works at the front of borders and in containers.
(Above right) Fashion Monger looks lovely in a vase, the border and in containers with its splash of color on a white base. Originally introduced in 1955, this colarette variety has a charming retro feel.
(Above left) Engelhardt’s Matador, a decorative variety, as the name suggests, really makes a dramatic presence in the border with its double magenta flowers. Partner it with contrasting colors for a real statement.
(Above middle) Blackberry Ripple sounds delicious and looks delicious with splashes and drizzles of crimson and purple. Position this semi-cactus variety in the border with similar colors.
(Above right) Chilson’s Pride, an informal decorative dahlia, has softly pretty pink petals around a pale cream centre that blends in an harmonious border scheme, and is an equally lovely cut flower.
(Above left) Chat Noir is loved by many for its rather sumptuous garnet to near black semi-cactus form, in the garden and in the vase. It looks dramatic in blocks in an exotic border scheme.
(Above middle) Crossfield Ebony, a pompon variety, has a steady stream of delightful, darkly maroon spheres ideal for the vase and in a mixed border. The small size of flowers works attractively mingling with a cottage-styled border.
(Above right) Babylon Purple, with its purple and red dinner-plate blooms held on long stems, is stunning en masse with dark leafed plants and also makes an exceptional cutting flower.
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