How to grow Dahlia

How to grow Dahlias

It's no surprise that Dahlias have found renewed popularity in recent years. No longer considered old fashioned and vulgar, their showy blooms fit well with modern trends towards strong colours and intriguing flower shapes.

How to grow Dahlias

It's no surprise that Dahlias have found renewed popularity in recent years. No longer considered old fashioned and vulgar, their showy blooms fit well with modern trends towards strong colours and intriguing flower shapes.

Dahlias are a diverse genus, ranging from compact bedding plants, through to tall feature plants for the back of the border. They lend themselves to a broad range of garden styles from carefully coordinated hot colour schemes, to the eclectic symphony of a traditional cottage garden. They make superb cut flowers too!

Growing them isn't as hard as you might think - read on to learn how to grow Dahlias, or browse our range to buy your Dahlias online.

Dahlia mix

Seeds, tubers or plug plants?

You may see Dahlias offered for sale as seed, tubers or plug plants. Tubers are the easiest way to grow Dahlias. Tubers are mature, bare root plants which can be planted directly into the ground when they soil warms up a little from mid-April. Alternatively they can be potted into large, 3 litre pots and grown on in a frost free greenhouse, before planting into their final positions outdoors.

dahlia tubers and plants

Plug plants are a little more delicate requiring potting up and growing on in frost free conditions during spring. They can be hardened off and planted out in May once they are well grown.

If you have greenhouse space or a bright windowsill then bedding Dahlias are easily grown from seed. Growing Dahlias from seed is by far the most cost effective choice if you require large numbers of plants. Sow them from February to April in free draining seed compost, maintaining a steady temperature of 18-20C. Transplant seedlings into individual cells or small pots once they are large enough to handle and have a well-established root system. Grow them on in warm conditions, repotting when necessary until they are large enough to be hardened off and transplanted outdoors in late spring and early summer.

How to plant Dahlias

Dahlia plants are half-hardy, so it's important to keep them protected from frosts. Once all risk of frost has passed, Dahlias can be acclimatised to outdoor temperatures over 7-10 days before being planted into their final flowering positions. Choose a sunny spot in moist, fertile, well-drained soil. Prepare the soil by digging in plenty of well-rotted manure or compost and incorporating some blood, fish and bone fertiliser to feed the plants.

Dig a hole large enough to accommodate the rootball, ensuring that it sits at the same depth in the soil as it was in the pot. Tubers should be planted so that the stump of the previous year's stem, sits just above ground level, with the 'sausage-like' tubers covered completely by the soil.

canes support dahlias

Taller varieties will almost certainly need staking with sturdy canes or narrow wooden posts to support their stems. It's a good idea to insert stakes into the planting hole before positioning the plant. This will avoid damaging the root system later on. Settle the soil after planting by giving it a good soaking with water.

At this stage, it's a good idea to put some slug protection in place. Use copper tape to protect container grown plants. Dahlias planted directly into the soil can be protected using slug traps, pellets, or physical barriers with rough surfaces such as a mulch of bark chips, crushed eggshells or sharp grit.

Getting the best from your Dahlia plants

When Dahlia plants have 4 set of leaves, pinch out the growing tip of each stem to encourage bushier growth. For the biggest blooms and strongest flower stems, select 5 to 7 main stems per plant and allow these to develop, removing all other side shoots that develop in the leaf axils below the main terminal bud.

As they increase in height, gently tie them to their supporting stakes using soft garden twine.

Feed and water Dahlias regularly throughout the growing season. Always water at the base of each plant, to avoid wetting the foliage. Use high potash feed every two weeks, once the flower buds begin to form. This will encourage more buds to develop throughout the summer.

Deadhead faded dahlia flowers ruthlessly to encourage more blooms to be produced.

Dahlia border

Storing Dahlias overwinter

In very mild areas, it may be possible to leave your Dahlia plant in the ground over winter. Be sure that they soil is very free draining and cover them with a thick layer of a dry mulch such as bark chips or straw.

In colder areas Dahlia tubers can be lifted in autumn and stored over winter in trays of peat or sand, in a cool but frost free position. Here's how to go about it ...

  • In autumn, cut back the foliage and lift the tubers from the ground with a garden fork.

  • Place the tubers in a well ventilated, dry location such as a garden shed or greenhouse and allow them to dry off before cleaning away any remaining soil.

  • Trim away any fine roots, leaving just the main tubers.

  • Place into seed trays of multi-purpose compost or dry sand, covering the tubers but leaving the crown of the plant just above soil level.

  • Store in a cool frost free location. They won't need light at this stage, so a garden shed will suffice but make sure that they are covered with fleece or a thick layer of newspaper on particularly cold nights.

  • Check tubers regularly and throw out any that show signs of rotting.

  • Replant in spring for another fabulous display!

drying dahlia tubers

With so many different colours, flower forms and sizes to choose from you may find it hard to narrow your choices down. Be bold and create a Dahlia bed. Don't be afraid to experiment with extraordinary colour combinations for an exotic riot of colour. For a more refined display try picking just a few colour coordinated varieties that can be repeated through mixed borders.


Sue Sanderson T&M horticulturalist

Written by: Sue Sanderson

Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman's nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.

#YourTMGarden

For the chance to be featured, share your plant pictures with us
on Instagram by using the hashtag #YourTMGarden

Join the T&M Gardener's Club

JOIN NOW
RedEye

Join the T&M Gardener's Club