How to plant out dahlias

Discover detailed advice on planting out dahlias, including the soil they enjoy and how to encourage more blooms.

Do it:

Mar, Apr, May

Takes just:

15 minutes

At its best:

Jul, Aug, Sep

Whether you’re looking for a bright bedding display, flowers for cutting or reliable border plants, it’s hard to beat the variety offered by dahlias. Dahlias come in many sizes, so there's one for every border, and small forms can also be grown in pots. While you can plant dahlia tubers directly into the soil, it's good to give them a head start under glass, before hardening off and planting out in late May. This not only ensures large, healthy plants with lots of flowering potential, but also allows you to take cuttings and increase your stock, creating a bigger display.

Planting dahlia tubers in pots or trays indoors from March and April encourages stems to develop, forming a bushy plant that will bear more flowers this summer. Choose a pot large enough to accommodate the tuber, and fill around it with multi-purpose compost leaving the top of the tuber showing. New shoots should appear within weeks.

When you plant them out, leave 15cm to 45cm between plants, depending on the ultimate size of your variety. Avoid wet or shady sites, and dig the area over deeply before planting, incorporating lots of compost, to keep these hungry plants in top condition.

You will need

Wooden stakes

Well-rotted manure

Garden twine

Secateurs

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Before planting out your dahlias, hammer several 1.2m stakes into the soil. Make sure they are firmly placed and unlikely to wobble, as these will provide support for your dahlias.

Dig a hole at the base of each stake, about twice as wide as the dahlia rootball.

Add a deep layer of well-rotted manure, home-made compost or or peat-free multipurpose compost to the bottom of the hole, to increase nutrients and aid moisture retention.

Water each plant thoroughly before gently removing it from its pot. Tease out the roots, then settle the rootball into the hole.

Plant each rootball deeply, so the top is 5-8cm below the soil surface. This will help to support the brittle stems.

Using your heel, firm the soil around the plant, then water well so it settles the soil and soaks down to the roots.

Spread a 5-7cm-deep layer of mulch over the soil around the plant. This should stop it drying out in summer.

Weave garden twine back and forth between the stakes, running it at different heights to hold the stems.

Once the plants are 30-50cm tall, cut out the tips of the main stems, to encourage side shoots to form.

Water generously when the weather is dry, and add liquid fertiliser every two weeks. Cut flowers as required.

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Cover tender new shoots with fleece on frosty nights, so they aren't damaged.

Discover more ideas and inspiration

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