Dahlias are the showstoppers of the late summer garden, delivering an explosion of colour just when everything else is starting to look tired. If you've ever wandered through a garden centre in spring and been tempted by those gnarly tubers promising dinner-plate-sized blooms, or felt slightly overwhelmed by the hundreds of varieties available, this guide is for you.
I'll be honest, dahlias have a reputation for being a bit fussy, and in some ways, they are. They're not the sort of plant you can stick in the ground and forget about, and often get ravaged by slugs or drought. But the payoff for a bit of extra care is absolutely spectacular, and once you understand their needs, they're surprisingly straightforward to grow successfully.
Dahlias originated in Mexico, which immediately tells you something important about their preferences – they love warmth and hate frost. In the UK, this means treating them as tender perennials that need protection over winter, rather than hardy plants that can stay in the ground year-round.
The "bulbs" you buy aren't actually bulbs at all, they're tubers, more like small potatoes with growing points called "eyes." This distinction matters because it affects how you plant, store, and propagate them.
There are thousands of dahlia varieties, but they're generally classified by flower form and size which are listed below so you can easily identify which types of Dahlias you want to grow in the UK.
For beginners, I'd recommend starting with decorative or semi-double varieties in the 10-15cm flower size range. They're reliable, forgiving, and still make a spectacular display without requiring the intensive staking that giant varieties need. They can be grown in even the most miniature gardens at the back of flower beds and will ensure that you start successfully before moving onto increasing all sorts of other, more picky plants!
Before diving into the detailed how-to, let's establish the non-negotiables for dahlia success. Get these fundamentals right, and you're already halfway to spectacular results. If you just wack in some Dahlia tubers and hope for the best, you're bound to struggle, so a bit of preparation is key, Ninjas!
Dahlias are completely intolerant of frost – even a light touch will blacken foliage and kill plants instantly. In the UK, this means a growing season from late May (after the last frost) until October/November (the first hard frost). That's roughly 5-6 months of active growth, which is plenty of time for a full flowering cycle.
Dahlias are sun worshippers that produce their best flower displays in full sunlight. They'll survive in partial shade but expect reduced flowering, weaker stems, and increased disease susceptibility. Morning sun is particularly important for drying dew from foliage and preventing fungal problems.
Waterlogged soil is the quickest way to kill dahlia tubers. They need moisture-retentive but free-draining conditions with plenty of organic matter. Heavy clay soils must be improved with grit and compost, while sandy soils need organic matter to retain nutrients and moisture.
Those spectacular, large flowers and tall stems need shelter from battering winds. A location with natural protection from fences, hedges, or buildings is ideal. In exposed areas, artificial windbreaks may be necessary.
Dahlias are notoriously hungry plants that respond dramatically to good nutrition. From planting through to first frost, they need regular feeding – initially with balanced fertiliser, then switching to high-potash feeds once flowering begins.
Most dahlia varieties begin flowering 8-12 weeks after planting, typically from mid-July onwards. Early varieties may start in late June, while slower types don't hit their stride until August. This makes Dahlias a very fast-growing flowering plant where you will see flowers in year one rather than waiting 2-3 years for herbaceous perennials grown from seed to flower.
The duration of flowering is where dahlias really shine – they flower continuously from their first blooms until killed by hard frost. In a typical UK season, that means 3-4 months of non-stop colour from July/August through October/November. Some years, in mild autumns, they'll continue flowering into early December.
While dahlias flower for months, their peak performance is usually August through September when established plants are producing their largest, most prolific displays. This perfectly fills the late summer gap when many other garden plants are looking tired.
Daily Flower Production: At peak season, a mature dahlia plant can produce 2-3 new flowers daily, with each flower lasting 4-7 days depending on weather conditions. This means constant colour and an abundant supply of cut flowers throughout the season.
Timing is everything with dahlias. The golden rule is that they cannot tolerate any frost, so don't even think about planting them outside until you're confident the last frost has passed. In most of the UK, this means late May to early June, though you might get away with mid-May in the south.
If you're itching to get started earlier, you can start tubers indoors in pots from March onwards, then transplant them outside once the weather warms up. This gives you a head start and earlier flowers, but it's not essential.
Location is crucial. Dahlias need:
Proper soil preparation makes the difference between adequate dahlias and show-stopping specimens. Start preparing your dahlia bed in autumn or early spring, well before planting time.
Dahlias prefer slightly acidic to neutral soil with a pH between 6.0 and 7.0. If you're unsure about your soil pH, invest in a simple test kit – it's worth knowing.
This cannot be overstated. If water sits on the surface after heavy rain, you have a drainage problem. Incorporate coarse grit, sharp sand, or perlite into heavy clay soils. In extreme cases, create raised beds or mounded planting areas.
Dig in generous amounts of well-rotted manure or garden compost. Dahlias are heavy feeders, and rich soil produces the best results. A wheelbarrow load per square metre isn't excessive.
Heavy clay soils benefit from the addition of organic matter to improve structure and drainage. Sandy soils need organic matter to retain moisture and nutrients.
Work the soil to a depth of at least 30cm, removing any weeds, stones, or debris. The effort you put in at this stage pays dividends later.
Before planting, examine your tubers carefully. Healthy tubers should be firm with visible growing points (eyes) – small bumps or shoots on the crown where the old stems were. Discard any that are soft, mouldy, or obviously damaged. If they feel squishy or smell compost them immediately.
Start tubers in pots indoors 4-6 weeks before your intended outdoor planting date. Use multipurpose compost, plant with the crown just above soil level, and keep in a warm, bright location. Water sparingly until growth appears, then increase as shoots develop.
Wait until the soil has warmed and the last frost has passed. Dig holes 10-15cm deep and 30-60cm apart, depending on the variety size. Place tubers horizontally with the crown (where stems emerge) about 5cm below the soil surface. Cover with soil and water gently.
Install stakes at planting time, before the dahlias get established. It is vital to stop them from flopping over or becoming damaged. They grow so quickly, get your stakes in sooner rather than later, and tie them in with strong or jute twine wherever possible. Trying to stake mature plants without damaging roots is nearly impossible. Use sturdy canes or metal stakes at least 1.5m tall for medium to large varieties.
Once your Dahlias are growing (at a rapid rate before your eyes) its time to think about how much you need to water, feed and protect them from drying out. As they grow super fast they are really quick to need yout attention, which is why sometimes beginner gardeners get a fright at how needy Dahlias can be!
Young plants need regular watering to establish, but avoid overwatering, which can rot tubers. Once established, water deeply but less frequently – this encourages deep root development. During hot, dry spells, dahlias may need watering daily.
Dahlias are notoriously hungry plants. Start feeding 2-3 weeks after planting with a balanced fertiliser. Once flower buds appear, switch to a high-potash feed (tomato fertiliser works well) to encourage blooming. Feed every 2 weeks throughout the growing season.
Apply a 5cm layer of organic mulch around plants, keeping it away from the stems. This conserves moisture, suppresses weeds, and gradually improves soil structure as it decomposes.
As plants grow, tie them to stakes using soft ties or string. Check ties regularly and loosen if they're cutting into stems. Tall varieties may need multiple stakes or a cage system.
Pinching Out: When plants reach about 40cm tall, pinch out the growing tip to encourage bushier growth and more flowers. This may delay first blooms by a week or two, but results in much better plants overall.
Deadheading: Remove spent flowers regularly to encourage continuous blooming. Cut back to the first pair of leaves or side shoots. This prevents energy from going into seed production and keeps plants flowering until frost. This is key if you want blooms well in autumn, Ninjas!
Disbudding: For larger flowers, remove side buds, leaving only the terminal bud on each stem. This concentrates the plant's energy into fewer, larger blooms – essential for exhibition-quality flowers. This may feel cruel, but it's the best way to get fewer larger flowers, especially if planning to grow your own wedding bouquet!
Side Shooting: Remove shoots growing from leaf joints to maintain plant shape and direct energy into main stems and flowers. A bit like the method used for pinching out tomatoes when growing them from seed.
Pest and Disease Management: Watch for aphids, slugs, earwigs, and red spider mites. Aphids are the most common problem – blast them off with water or use insecticidal soap. Slug damage is worst on young growth – use your preferred slug control method.
I receive numerous emails each month in the summer about slug-nibbled dahlias, yellow leaves, and a lack of flowering. My forum is often full of the same questions, so let's dive into what problems you may encounter when growing Dahlias, especially in poor weather years of drought or heavy rainfall!
Usually caused by insufficient light, over-feeding with nitrogen (which promotes leaves over flowers), or plants that are too young. Ensure 6+ hours of daily sun and use high-potash fertiliser once buds appear. Avoid mixed fertilisers which have a higher level of nitrogen, tomato feed, or comfrey tea are brilliant for creating huge Dahlia flowers.
Often indicates insufficient light or over-rich soil with too much nitrogen. Ensure adequate support and avoid high-nitrogen feeds once established.
It can indicate poor drainage, compacted soil, or pest damage below ground. Check that tubers aren't sitting in waterlogged conditions or heavy clay soil rotting away!
Normal on lower leaves as the season progresses, but extensive yellowing may indicate overwatering, poor drainage, or viral infection.
These pests love dahlia shoots. Use organic slug pellets, beer traps, or encourage natural predators like frogs and hedgehogs.
Choosing the right varieties makes all the difference for beginners. Here are my top recommendations based on reliability, ease of growth, and garden performance:
'Bishop of Llandaff' – Semi-double, red flowers with dark bronze foliage. Compact growth (90cm), reliable, and stunning contrast. Perfect for beginners.
'Café au Lait' – Huge (25cm+) cream and pale peach decorative flowers. Dramatic impact but needs good staking. Worth the effort.
'David Howard' – Orange decorative flowers with dark foliage. Medium height (120cm), reliable bloomer, excellent cut flower.
'Labyrinth' – Mixed colours, pompon type. Compact growth (60cm), prolific flowering, great for containers.
'Gallery Art Deco' – Dwarf bedding type (30cm) with orange and yellow flowers. Perfect for containers or front of borders.
'Moonfire' – Yellow flowers with red tips, dark foliage. Single flowered, reliable, and loved by pollinators.
'Thomas A. Edison' – Deep purple decorative flowers. Classic variety, reliable, and creates dramatic colour impact.
'Labella Maggiore' series – Range of colours, compact growth (40cm), long flowering season. Excellent for beginners and containers.
'Mystic Illusion' – Purple flowers with dark foliage, compact growth. Striking colour combination and very reliable.
'Garden Princess' – Range of bright colours, compact growth (30cm). Perfect for containers and inexperienced growers.
Container growing is an excellent option for beginners, renters, or those with limited garden space. It also makes winter storage much easier since you can simply move pots to frost-free locations.
Container Requirements:
Compost: Use quality multipurpose compost mixed with slow-release fertiliser granules. Avoid garden soil which becomes too heavy and may contain pests or diseases.
Varieties for Containers: Focus on compact varieties like Gallery, Labella, or Garden Princess series. Avoid tall or spreading varieties unless you have very large containers.
Care Differences: Container plants dry out faster and need more frequent watering and feeding. Check daily in hot weather and feed weekly with liquid fertiliser once flowering begins.
This is where many beginners come unstuck, but it's actually straightforward once you understand the process. In the UK's climate, dahlia tubers must be lifted and stored over winter to prevent frost damage.
When to Lift Tubers: Wait until the first hard frost blackens the foliage, usually October or November. Don't rush – tubers continue developing until foliage dies back naturally.
Lifting Process:
Preparing for Storage: Once dried, remove any remaining soil with a soft brush. Inspect each tuber carefully, discarding any that are damaged, soft, or showing signs of rot. Dust cut surfaces with fungicide powder if available.
Storage Methods:
Traditional Method: Store in wooden boxes or paper sacks filled with slightly moist peat, vermiculite, or wood shavings. The storage medium should be barely damp – not wet or completely dry.
Modern Method: Store in perforated plastic bags with barely moist vermiculite or wood shavings. This provides good humidity control while allowing air circulation.
Alternative Method: Some gardeners successfully store tubers in newspaper-lined cardboard boxes in cool, dry conditions. This works well for experienced growers but can lead to dessication in centrally heated homes.
Storage Conditions:
Checking Stored Tubers: Inspect monthly through winter. Remove any showing signs of rot immediately to prevent spread. If tubers are shrivelling, increase humidity slightly. If condensation appears, improve ventilation.
In-Ground Protection (Mild Areas Only): In very sheltered locations with excellent drainage and mild winter temperatures, some gardeners successfully leave tubers in the ground with heavy mulch protection. This is risky in most of the UK and not recommended for beginners or valuable varieties.
Pot Storage: Container-grown dahlias can be stored in their pots in frost-free locations. Cut back foliage and move containers to an unheated greenhouse, garage, or shed. Water very sparingly – just enough to prevent complete desiccation.
Division and Propagation: Spring is the ideal time to divide large clumps before replanting. Each division needs at least one growing point (eye) and some tuber to provide energy for initial growth. This is an excellent way to increase your collection or share with friends.
In late February or March, check stored tubers and remove them from storage material. Look for signs of new growth – small shoots or swelling buds indicate tubers are ready for action.
Pre-planting Preparation:
Starting Growth: Place tubers in shallow trays of moist multipurpose compost with growing points just above surface level. Keep in a warm (15-20°C), bright location and water sparingly until shoots appear.
Hardening Off: Once shoots are 10-15cm tall and outdoor temperatures are warming up, begin hardening off process. Gradually expose plants to outdoor conditions over 7-10 days before final planting.
Colour Schemes: Dahlias come in every colour except true blue. Plan colour combinations carefully – the vibrant colours can clash spectacularly if not thoughtfully arranged. Hot colours (reds, oranges, yellows) work well together, as do cool colours (pinks, purples, whites).
Height Considerations: Plant tall varieties at the back of borders, medium varieties in the middle, and compact varieties at the front. Allow adequate spacing – overcrowded dahlias compete for light and air circulation.
Companion Planting: Dahlias pair beautifully with late summer perennials like rudbeckia, asters, and ornamental grasses. Annuals like cosmos, zinnias, and marigolds extend the colour theme.
Cut Flower Production: If growing for cutting, consider dedicated cutting beds where you can plant in rows for easy maintenance and harvesting. Cutting regularly actually encourages more flower production.
Spring (March-May):
Early Summer (June-July):
Late Summer (August-September):
Autumn (October-November):
Winter (December-February):
Soil Temperature: Use a soil thermometer to check soil temperature reaches 15°C before planting. Cold soil slows growth and increases risk of tuber rot.
Companion Feeding: Plant nasturtiums nearby to attract aphid predators, or grow sweet alyssum to encourage beneficial insects.
Weather Protection: In exposed areas, create windbreaks using temporary screens or plant permanent hedging to protect tall varieties.
Record Keeping: Keep notes on variety performance, flowering dates, and any problems. This information proves invaluable for planning improvements.
Photography: Take photos throughout the season to record successful combinations and remind yourself of varieties you want to repeat or avoid.
Planting Too Early: Patience is crucial. Cold, wet soil kills more dahlia tubers than almost anything else. Wait for warm soil conditions.
Insufficient Staking: Install stakes at planting time, not when plants are already falling over. Trying to retrofit supports damages established root systems.
Overwatering Young Plants: Newly planted tubers need moisture to establish but waterlogged conditions cause rot. Water carefully until active growth begins.
Neglecting Pest Control: Small pest problems become big ones quickly. Regular inspection and early intervention prevent serious damage.
Poor Storage Conditions: Too wet, too dry, too warm, or too cold storage kills tubers over winter. Aim for consistent, moderate conditions.
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Growing dahlias successfully in the UK requires attention to their specific needs, but the rewards are spectacular. From the first shoots emerging in spring to the final flowers before frost, dahlias provide months of garden interest and cutting material. With proper soil preparation, appropriate variety selection, and careful winter storage, even beginners can achieve outstanding results.
The key is starting with realistic expectations and reliable varieties, then expanding your collection as experience grows. Whether you're drawn to the architectural drama of cactus varieties or the cottage garden charm of single flowers, there's a dahlia perfectly suited to your garden and growing style.
Remember that dahlia growing is as much about the journey as the destination. Each season brings new varieties to try, techniques to master, and combinations to explore. The winter storage period, rather than being a chore, becomes an anticipation-filled pause before the excitement of spring planning begins anew.
Happy Gardening, Ninjas!
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