To grow a dahlia in a pot

Which dahlia to choose for growing in a pot?

Today there are nearly 20,000 horticultural varieties of Dahlia. This gives gardeners unlimited choice! If all dahlias are suitable for container growing, prioritise varieties with moderate vigour. The largest dahlias sometimes exceed 1.5 m in height in fertile soil, with a spreading of 45 to 80 cm, and flowers sometimes more than 25 cm in diameter! Needless to say, in a pot they are not the most suitable.

With a compact, ramified habit, indifferent to bad weather, and just as floriferous as the larger dahlias, dwarf dahlias are particularly suited to pot or container growing. In addition, they require no staking, no pinching and no pruning — simply remove spent flowers — and withstand strong winds and heavy rain better than their tall relatives, the giant dahlias! Their height ranges from about 30 to 80 cm. They are miniature replicas of the tall varieties… less demanding!

Among our favourites, I suggest Dahlia ‘Bluesette’ (dwarf, 40 cm high by 30 cm spread), the dwarf cactus dahlia ‘Blue Record’ which does not exceed 60 cm in height, the Dahlia ‘Red Pygmy’, another splendid dwarf cactus dahlia, our Dahlia collection ‘Happy Single’, the dwarf Dahlia ‘Gallery Valentin’ with flowers resembling large clementines, or the Dahlia ‘Priceless Pink’, a small peony-flowered dahlia variety. Dahlia ‘Senior’s Dream’ is a small ornamental dahlia that will also suit container growing.

Dwarf dahlias ‘Priceless Pink’ and ‘Senior’s Dream’

When and how to grow a dahlia in a pot?

When to plant?

Prefer spring planting, from March to April, and until May in cooler regions. Dahlia tubercles are planted after last frosts. Wait until any risk of frost has passed before putting pot outside.

Choose the right container

Choose a drained container at least 30 cm in diameter to ensure good stability and optimal development. Dahlia roots need room! For very low-growing varieties, opt for a deep planter rather than a pot.

Choose a pot large enough for your Dahlia to flourish fully

Which substrate to use?

Dahlia is a greedy plant: to flower well and gain vigour, simply provide good planting compost and water very regularly with a good fertiliser. Substrate must be rich, fresh and well drained: stagnant moisture would encourage rotting of tubercles. Plant in a mix of planting compost of geranium type, which retains moisture well, enriched with a little river sand to improve drainage and a slow-release organic fertiliser, for example a handful of roasted bone meal powder or blood meal to promote development and flowering.

How to plant?

Do not hesitate to mix several small varieties together to create multicoloured container plantings; in that case, keep a distance of 30 to 50 cm between each tubercle.

• Prepare a large pot or planter with drainage by spreading a layer of clay pebbles or gravel at the bottom
• Place your tubercle
• Cover with the rich, free-draining mix and crumble the soil well to fill without air pockets
• Your dahlia should be covered with about 6-8 cm of soil
• Water generously
• Scatter a few slug pellets on the surface to give first shoots a chance to emerge
• To retain freshness between waterings, once young plants are well established, consider mulching with hemp or flax chips, for example

Where to place it?

Give pot sunniest, warmest spot! Good light exposure ensures abundant flowering. Also position it sheltered from strong winds and rain to protect delicate flowering.

Dwarf dahlias, Hydrangea ‘Limelight’, Carex oshimensis ‘Evergold’, Geranium ‘Rozanne’ (© Friedrich Strauss)

How to care for a potted dahlia?

Watering

During growth, Dahlias need plenty of water, especially in hot summer weather! Throughout the growing season, be particularly attentive to their water needs, as the substrate dries out faster than in open ground. You will need to pamper your dahlia! The rootball must not dry out completely between waterings. Water copiously during bud growth, once or twice a week, as soon as the substrate becomes dry; it should remain fresh. Water at base of plant and not on leaves to avoid diseases such as powdery mildew.

There are potting mixes (Water Grain) ready to use that feed plants and reduce watering, specially designed for flowers grown in pots or window boxes. Made from turfs, they increase water storage capacity.

Also consider water retainers (such as ‘Hydro-retainer Fertisob’). They come as granules to mix with planting soil. They retain water in soil when abundant and release it to plants as needed when it becomes scarce. They can significantly reduce water requirements.

Fertilisation

Dahlias are voracious, even more so when grown in a pot! Potting substrate depletes faster than in open ground; add a fertiliser for flowering plants to the watering water every two weeks from June to October to encourage growth.

Pruning

Easy to grow, small dahlias require neither pinching nor pruning. However, if tubercules produce only a single stem, pinch the terminal shoot to encourage branching.

Simply remove faded flowers as you go to encourage new flowers and extend flowering. Remove small shoots at the axil of leaves: the heads will be larger as a result.

Overwintering

Dahlias are extremely tender and susceptible to frost. When first frosts appear, in October or November, protect them from freezing! Dahlias can overwinter directly in their pot. Before overwintering:

1. Cut faded stems to 15 cm above soil level
2. Store pots protected from light, rodents and frost in a dry, airy place (dry cellar, or simply your garage) where temperature should not exceed 5-8°C
3. You can bring pots out in spring from April–May depending on region, as soon as last frosts have passed and temperatures have warmed

Note: in regions with mild winters, pots can be left in place if protected by a thick layer of mulch, ideally made of dead leaves or straw, and by wrapping hessian or bubble wrap around the container: potted plants are more sensitive to cold, being more exposed.

Repotting

Each year in spring, it is important to repot dahlias into a brand-new substrate that is nutrient-rich and well drained.

To learn more

Discover everything you need to know about dahlias in our comprehensive guide.