How to plant and grow Dahlias

Dahlias

Dahlias are a ‘must have’ flower for every Summer garden! In fact they are loved for their long flowering periods as they can bloom from the summer up until the first frosts. Dahlias bring colour and character and are happy to be placed in a dry, sunny position.

Planting dahlias in the garden

Once the risk of frost has past, April/May, find a sunny position with fertile, moist but well-drained soil. Alternatively, you can start them off in indoors in pots in March/April and keep them in a frost-free location like a greenhouse before transferring them outside after the last frosts. Position the dahlia tubers just below the soil surface, covering your tubers with approx. 3cm (1-2″) of soil. Allow approx. 30cm (12″) spacing between each tuber. (The spacing may vary depending on the final size of the variety.) Ensure to plant your tubers the right way up by locating the old stem – this is the top of the dahlia.

When planting in the garden, mulch over to protect them from the risk of any late frost, douse the hole with a watering can full of water and cane as you plant.

Pom Pom Dahlias
Pom Pom dahlias

Harts’ Hint
“After about 5-6 weeks, you may need to start protecting the new dahlia shoots from slugs and snails by using slug pellets or by removing the nocturnal pests at night!

Planting dahlias in pots

Dahlias can spread quite vast so we advise planting 1 x dahlia tuber in a 2 to 3 litre pot or 30cm (12″) in diameter and fill with a good-quality, multi-purpose compost. Ensure sure the pot has good drainage because the tubers will rot if left to sit in water. If the pot only has 1 or 2 holes, you can add more with a drill to prevent the tuber from rotting. Adding good draining elements like bark to the base of the pot will help with drainage. Use a slow-release fertiliser to promote strong growth and stake when planting.

Lay your tuber flat in the container with the eye or sprout, if there is one, facing upwards. Plant with the eye just above the soil surface.

Harts’ Hint
Dahlias will flower throughout the summer and dead-heading them will prolong their flowering period.

caring for dahlias

  • You can feed your Dahlias with a diluted Tomato feed every 2 weeks.
  • Support Dahlias with canes on planting and tie in as growth develops.
  • When your Dahlias reach about 40cm in height, pinch out the growing tips with your thumb and forefinger or use a sharp knife. This will encourage branching.
  • Water once a week with a good amount not just a little sprinkle.
  • Deadhead flowers as they fade.

Overwintering:

  • Once the first frosts have blackened the foliage, cut the plants back to the ground.
  • In well-drained soils or in mild parts of the country, you can keep your dahlias planted in the ground over winter, mulch them over deeply with 6-7cm (2.5″) of bark chips or compost to protect them from frost. In colder climates or heavier soils, lift and store your tubers over winter. Replant the following spring. 
  • If you are lifting and storing your dahlias for winter, ensure to clean off any soil and dry them before storing. Keep the corms in a cool, dry spot like a garage or shed.
  • If in pots, stop watering at the end of summer and bring them indoors for winter to protect against frost. Place back outside once the danger of winter frosts has passed. 

Lifting and Storing over winter:

  • Cut back foliage and carefully lift the tubers out of the soil.
  • Allow the tubers to dry off naturally and then clean away any soil. 
  • Trim the stems back to 15-20cm and cut off any fine roots.
  • Make sure the tubers are completely dry before storing them into open trays or boxes. Pack with dry compost or dry sand. Leave the crowns exposed. 
Lifted Dahlia tuber before cleaning and storing for winter.

Video on Planting Dahlias

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Advice about cutting

This question was asked by
Paul C

Hi. I planted out some rose lilies for cutting in a cutting bed and I’ve just started bringing them in, delighted with the results.
I just want some advice about whether they will repeat flower next year and if there is any way I should cut or feed them to improve the chances. I am so delighted with them we will be buying new stock anyway but would like this to become a recurrent bed if at all possible. Any advice would be much appreciated.

Hi Paul
You need to leave a good amount of stem on them to die back naturally to feed the bulb for the following year. If they are cut too short then they probably won’t flower for a few years. I’d suggest leaving atleast 2ft of stem if you can. You can give them a diluted tomato.feed to help them every 2 weeks.

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