Dahlia: planting, growing, care and flowering

Long, straight stems carry cactus, pompom, collarette or ornamental blooms in a dazzling range of shapes and colours: the dahlia, native to Mexico, flowers from June through to October. Give it full sun and rich, well-drained soil that never stands in water, and it will keep producing new flowers until well after summer is over.

Dahlia at a glance

Name	Dahlia
Family	Asteraceae
Type	bulb plant
Height	8 to 60 inches (20 to 150 cm) depending on the variety
Exposure	full sun
Soil	enriched ordinary soil
Flowering	June to October

Here is the advice on how to care for them to produce magnificent dahlias.

Planting dahlia

It is important to plant your dahlia correctly, since this step is crucial to your plant’s growth and flowering.

Planting dahlia bulbs

Preparing cuttings is the simplest, fastest, and most common planting technique to multiply your beautiful dahlia flowers.

• Dahlia bulbs are best planted during the months of April and May, when the last frosts are past.
• Dahlia prefers rather rich and well drained soil.
• Plant them about 2 to 4 inches (5 to 10 cm) deep, and space the bulbs 30 to 40 inches (80 to 100 cm) apart, because dahlia requires sunlight and likes having space to spread out!

If you feel that the soil in your garden is rather poor, enrich it upon planting with organic soil conditioner or compost.

Sowing dahlias

It is perfectly possible to sow dahlias from seed, but this technique requires an extensive know-how that only true experts can master.

• To sow, start with sowing in a tray in early March, repot in April and transplant in the ground in May.

• Propagate through tuber division in spring.

Three ways to start dahlias, compared

The article describes three routes to new dahlia plants, and they differ above all in timing and in the skill they demand. Choose the one that matches the season you are in and your experience.

Whichever route you take, the plants go out only once frost is no longer a risk.

Pruning and caring for dahlias

Once properly settled in, dahlias require very little care, even though certain practices will help extend or boost blooming.

• Remove wilted flowers regularly (deadheading).
• Once stems are completely wilted, cut them as short as you can.
  
• Dahlia plants can resist freezing temperatures down to around 14° to 23°F (-5 to 10°C).
  In winter, it is important to protect the base of your plants with plant-based mulch.
• If you fear particularly strong freezing:
  At the beginning of winter, bring the tubers indoors when the first frost spells hit, and keep them in a dark, dry place until the following spring.

Watering dahlia

Dahlias are quite resilient, but appreciate being watered during extended dry spells.

Check that dahlia bulbs never get flooded or stand in stagnating water, since this would make them rot.

Well-drained soil guarantees that this kind of mishap doesn’t happen.

• Water dahlia without wetting its leaves. Doing this will help avoid any risk of disease.
• Water preferably in the evening to reduce evaporation and also save water.

• After planting dahlia or tuberous begonia tubers, keep the soil barely moist until shoots appear, since a leafless tuber absorbs little water and is prone to rotting in cold, waterlogged ground.
• Water dahlias deeply and less often rather than sprinkling a little every day, so moisture reaches the tuber zone and roots are encouraged to grow downwards instead of massing at the surface.
• Check the soil with a finger before reaching for the watering can: if it still feels damp below the surface, wait, since dahlias’ tubers can rot in soil that stays waterlogged.
• Dahlias grown in pots dry out much faster than those in open ground and may need watering every day in hot weather, as the limited volume of compost holds only a small reserve.

How to prolong dahlia blooms from summer to fall

Dahlia blooms can be extended even until after summer is over, sometimes even until the end of October.

• Add flower plant fertilizer once a week until the end of the blooming season.
• Remove wilted flowers regularly to avoid draining your dahlia and to spur appearance of new flowers.

• When deadheading, follow the spent stem down and cut just above a pair of leaves or a visible side bud, rather than snapping off only the flower head, which tends to leave an unsightly stub that may die back.
• Spent dahlia heads turn pointed and cone-shaped while unopened buds stay round and plump, so checking the shape before cutting avoids removing flowers that have yet to open.
• For many flowering and fruiting plants, such as tomatoes and container-grown bloomers, gardeners commonly recommend a high-potassium feed like tomato fertiliser, because high-nitrogen feeds tend to encourage leafy growth over flowers.
• Push stakes in at planting time and tie tall cultivars in as they grow, since a stake driven into an established clump can spear the tubers, and a snapped stem costs you that shoot’s blooms while the plant recovers.

Dahlia in winter

Although dahlia can spend the winter in the ground in mild-wintered areas, it can’t survive strong frost spells.

If you live in an area where the weather frequently drops below 23°F (-5°C), bringing your bulbs indoors before it freezes is your only hope.

• Wait for leaves to wither completely, and then cut them 4 inches (10 cm) above ground level.
• Pull out the rhizomes and let them dry off.
• Clean them with a brush.
• Keep them in a cool, dry and dark place.
• Replant them outdoors when the last frosts are past, in spring.

In other regions, protect your tubers with dead leaf mulch for instance.

Popular dahlia varieties at a glance

Dahlias range from knee-high patio types to towering dinnerplate cultivars, so the variety you pick decides how much staking and space you will need. The selection below gathers widely sold cultivars, arranged by flower form, height and colour.

Learn more about dahlia

Native to Mexico, a dahlia is a bulbous plant that has evolved into several dozen species.

There are cactus and semi-cactus dahlia varieties, pompom or ball dahlias, ornamental dahlias, and collarette dahlias, that provide for dazzlingly varied shapes and colors.

This is a plant that comes in a wide variety of blooms!

Its long flower-bearing stems stand tall and true, and produce beautiful flowers with many colors.

Read also:

• Dahlia imperialis, tall tree dahlias
• Red label dahlias to help you choose. It’s an honorific classification awarded to specific cultivars.
• Dahlia forcing, root and stem cuttings

Interesting dahlia cultivars

Among the many interesting dahlia cultivars, we’ve admired the following: ‘Aspen’, ‘Café au lait’, ‘Berliner kleene’, ‘Margareth kleene’, ‘Arabian night’, ‘bluesette’, ‘Deuil du roi Albert’, ‘Bishop of Llandaff’, dahlia ‘Bonesta’, dahlia ‘Chantal’…

There are many more!

→ Read also:

• All there is to know on planting bulbs
• Planting bulbs in clay or flooded soil

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