Growing Dahlias Successfully

When to plant dahlias?

The ideal time to plant your dahlias depends on your region’s climate. In colder regions, wait until after the last frosts, typically late April or early May, to plant them in the ground. Young dahlia shoots are sensitive to cold, so it’s essential not to rush.

If you’ve purchased bulbs packaged in bags, don’t worry—they can wait patiently until the right planting time. Just make sure to store them in a dry, dark, and frost-free place, such as a cellar or unheated garage. Good ventilation is also important to prevent mould from developing.

In milder climates, dahlias can be planted as early as mid-March. In any case, ensure the soil is well warmed (at least 10°C) to encourage quick and vigorous growth.

How to force dahlias to bloom?

If you want your dahlias to flower earlier in the season, you can force them by starting their growth before planting them out in the garden. This technique allows you to gain several weeks on their flowering period, perfect for a dazzling garden from early summer onwards.

To do this, if you have a greenhouse, a bright conservatory or cold frames, proceed as follows:

• Fill pots with rich, slightly moist compost.
• Plant your dahlia tubers at a shallow depth, just covered with a thin layer of compost. Make sure the “eyes” (the buds on the tubers) are facing upwards.
• Place the pots in a bright, frost-free location, with an ideal temperature between 15 and 18°C.
• Water lightly to maintain consistent moisture, but avoid waterlogging the compost. Within a few weeks, the tubers will begin to produce roots and young shoots.

Once the risk of frost has completely passed, usually around May, you can transplant your dahlias into the garden, taking care to preserve the root balls that have already formed. This will allow them to continue growing without interruption, for a quick and vigorous start in the garden.

Tip: If your dahlias grow a bit too quickly or become too tall before transplanting, lightly pinch back the young shoots to encourage branching and even more abundant flowering!

Where to plant dahlias?

Dahlias thrive in sunny, sheltered spots, essential for ensuring abundant flowering and robust plants. Ideally, choose a location that receives at least six hours of direct sunlight per day, as insufficient light may reduce flower production and make stems more fragile.

Dahlias prefer rich, well-drained soil that is slightly acidic to neutral. Heavy or waterlogged soil risks rotting the tubers. If your soil is dense or clay-based, improve it by adding sand, well-rotted compost, or potting mix to enhance aeration and drainage.

Dahlias integrate beautifully into mixed borders, where their colourful blooms can shine alongside other perennials or annuals. Compact varieties work perfectly for edging or container growing, ideal for decorating patios and balconies. Taller varieties, meanwhile, stand out as backdrops or focal points in flower beds.

How to plant dahlias?

Planting dahlias is a key step to ensure abundant and long-lasting flowering. Here are the steps to follow for successful planting in your garden:

• Dahlias thrive in rich, well-drained soil. Work the soil to a depth and width of about 20 cm to aerate it and facilitate root development. Mix in a handful of roasted horn powder or dried blood, which act as slow-release organic fertilisers. Break up the soil well to remove any clumps.
• Dig a planting hole wide enough to accommodate the tuber. Pour about 1 litre of water into the bottom of the hole to moisten the area without waterlogging the soil.
• Place the tuber in the hole with the “eyes” (buds) facing upwards. Cover it with about 8 cm of fine soil to protect the tuber while leaving enough space for young shoots to emerge easily.
• If planting a tall variety, insert a sturdy stake next to the tuber at planting time. This will avoid damaging the roots or tubers later when the plant has grown.
• For the tallest varieties, space them 80 cm to 1 m apart to allow them to flourish without overcrowding. For shorter dahlias, allow 30 to 50 cm between plants. These compact varieties are particularly well-suited to borders or small spaces.
• Once your dahlias start growing, applying a balanced fertiliser every 3 to 4 weeks will encourage growth and flowering. Also mulch around the base to retain moisture and suppress weeds.

Container growing tip:
Shorter dahlia varieties are ideal for patios and balconies. Use large pots with good drainage, filled with quality compost-enriched potting mix. Water regularly to maintain consistent moisture, and add liquid fertiliser every fortnight during the flowering period.

How to care for them?

Once your dahlias have resumed active growth, we recommend mulching the soil around the base of the plants. Mulching helps retain moisture, suppresses weed growth and protects the tubers from temperature fluctuations. Opt for natural materials like straw or wood chips.

Young dahlia shoots are often targeted by slugs and snails, particularly in early spring. To prevent damage, you can create natural barriers around the plants using crushed eggshells or use eco-friendly solutions like beer traps or organic slug pellets. Extra vigilance at this growth stage is essential to avoid irreversible damage.

Certain dahlia varieties (especially taller ones and those with large blooms) require staking. Installing supports at planting time prevents damage to the tubers. Tie the stems gently with soft ties to provide stability against wind or the weight of the flowers.

Throughout the flowering period, remember to deadhead spent blooms regularly to encourage new flowers. Prune stems just above a node to promote branching and extend flowering.

For a bushier, more compact plant, pinch out the main stem when it reaches about 15–20 cm in height. This technique stimulates new stem growth and, consequently, more flowers. If you prefer larger blooms, you can remove side buds to direct the plant’s energy into the main flower.

Water your dahlias deeply once or twice a week, adjusting frequency based on weather and soil conditions. Avoid wetting the foliage, as this can encourage diseases like powdery mildew. To prolong flowering and strengthen plants, apply a balanced fertiliser for flowering plants every three to four weeks.

Finally, inspect your dahlias regularly for signs of disease or pests. If you notice spots or discolouration on the leaves, treat promptly with natural solutions like horsetail manure or appropriate treatments. With these simple care tips, your dahlias will reward you with a vibrant explosion of colour all summer long.