Dahlias

Dahlia

• Position: full sun
• Soil: fertile, well-drained soil
• Flowering period: July to October
• Foliage: deciduous
• Hardiness: will need winter protection

Dahlias are indispensable for their long flowering season. They bring colour to the garden from July to late October.

How to grow

It is a perennial tuber plant. Dahlias perform best when grown in full sun, in fertile, well-drained soil. They are hungry plants. So add organic matter to the soil before planting to increase soil fertility.

Planting dahlias

What month should dahlias be planted? You can plant dahlia tubers into the ground in late April when the risk of frost has passed.

Planting depth

The tubers should be planted 10-15cm deep and space 40-50 cm apart. Protect young foliage from slugs and snails.

Planting dahlias in pots. For dwarf varieties choose a pot that’s at least 30cm wide and 30cm deep. For tall varieties choose a container that’s at least 50cm wide and 50cm deep.

Staking dahlias

Why support dahlias? Dahlia stems are prone to snap in windy weather. So tall varieties need staking.

Feeding

Here is our advice for feeding. When in flower, feed dahlias with a high potash liquid feed every 2 weeks from July to early September. You can use tomato feed.

Deadheading Dahlias

Cut off the spent flower heads and their stems regularly and you will be rewarded with a steady supply of blooms throughout the summer.

Spent flower heads or dead flowers can look similar to new flower buds. What’s the difference? Spent flower heads have a pointy shape. New buds are fat and slightly round.

Pruning dahlias. Remove regularly the dead flowers.

How to overwinter dahlias

Dahlias in the ground

Dahlia tubers are not frost-hardy. On wet ground and cold areas best to lift the tubers. When the leaves die down, cut the stems back to 5cm above ground level. Then dig up the tubers and remove the soil from the tubers. Turn them upside down and leave them to dry a little.

After that store them in a box or in a tray, filled with dry compost or vermiculite, in a dark, dry, frost-free environment. Check the tubers during the winter months for rotting. Remove any with rot.

In mild areas, you can leave the dahlia tubers in the ground. Cut the stems back to 10cm and cover the base of the plant with a thick layer of winter mulch to protect them from frost.

dahlias in pots

How to overwinter dahlias in pots? Cut back the foliage to 3-5cm above the soil in the pot. Then leave them to dry a little. After that store the dahlias in their pots in a dark, dry, frost-free environment.

When to buy dahlias

Dahlia tubers are available to buy from February in most garden centres in the UK in a range of heights and with different coloured flowers. Or order your tubers from dahlia specialists from January to March. The plants combine well with ornamentals grasses, Verbena bonariensis, Japanese anemones, and Achillea.

Verbena bonariensis