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How to plant out dahlias


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.

How to do it

Planting young dahlias: hammer in stakes


Once all risk of frost has passed, plant your dahlia in a sunny border outside, but first, hammer in a 1.2m  stake.

Planting young dahlias: dig a hole


Dig a hole at the base of the stake, about twice as wide as the rootball, then break up the subsoil.

Planting young dahlias: add a layer of well-rotted manure


Add a deep layer of well-rotted manure or peat-free compost to the bottom of the hole, to aid moisture retention.

Planting young dahlias: remove the plant from its pot


Water the plant, then gently remove it from the pot. Tease out the roots, then settle the rootball into the hole.

Planting young dahlias: plant deeply


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

Planting young dahlias: firm down and water


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

Planting young dahlias: spread a layer of mulch around the plant


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

Planting young dahlias: hammer-in additional stakes


Hammer additional wooden stakes into the soil around the plant, or group of plants, to support future growth.

Planting young dahlias: tie with twine


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

Planting young dahlias: cut the growing tips


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

Planting young dahlias: cut as required


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

Adam's tip

Plant dormant tubers outside from late April. Dig a hole 10-15cm deep and add a stake before planting.

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

Feed plants with liquid fertiliser every month, to promote strong growth and flower production.

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Talkback: How to plant out dahlias
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JMM31JAN 31/08/2013 at 15:43

Today, 31 August, I found some old dahlia tubers at the back of the garage which have several shoots. Is there any point in planting them out in tubs? If not, do I discard them, or re-stoore them over winter?

waterbutts 31/08/2013 at 16:48

I'm afraid the poor things are totally screwed up in terms of what season they think it is. They aren't hardy, so you can't leave them outside in the cold weather. But at the same time they have just got growing so it's going to be hard to persuade them to go back to sleep until next spring.

Do you have a heated greenhouse?

Gardenmaiden 31/08/2013 at 17:40

You could always use the shoots to take cuttings and have more dahlias next year.


JMM31JAN 04/09/2013 at 02:00

No, I do not have a greenhouse.  I wondered whether I should pot them in some compost and try and give them a little bit of growth before storing them for winter again?

Verdun 04/09/2013 at 10:51

Yes, that's exactly what ??ou should do

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