How to grow and care for Dahlias

A summer favourite amongst gardeners; Dahlias are the real showstopper flowers of the summer and early autumn season; but to keep them blooming in your garden you need to follow a few rules…

These summer-blooming and strikingly vivid flowers symbolise elegance, inner strength, change, creativity, and dignity.   The birth flower for August; Victorians believed that the dahlia symbolised a lasting commitment or bond between two people. 

Their blooms flower for prolonged periods compared to other flowers and offer such an incredible variety of colours; including red, pink, white, orange, yellow and purple.  Some with stripes, others with different colours at the tips, they come in such a variety of shapes and sizes from tiny pompoms to dinner plate varieties.

Planting dahlias 

  • Dahlias are tender tubers, so they don’t like frost.  
  • It is best to best to start the tubers in pots under cover of a greenhouse until the frosts have passed in late May/early June when you can then plant them out in the garden. 
  • Ensure you have lots of organic matter or compost in the soil and plant about 4-6cm deep.  
  • Pinch out the first flower bud/tips once 3 sets of leaves have formed to encourage a stronger plant, plus it will encourage side shoots which will lead to more flower heads.
  • Insert a stake when planting out to give immediate support and tie them in every couple of weeks.
To keep dahlias flowering in the garden there are few rules to follow: 

  • Plant your dahlias in the sunniest sheltered position you can.  The more sun they get, the better they'll bloom. 
  • They like fertile well drained soil.  Keep the soil moist but not wet by watering heavily once a week, or the tubers can rot.  In a drought water them every day as they are thirsty plants. 
  • They are fast growers and need feeding often, so provide this during the growing . season.  If you have them planted in pots; fertilise them fortnightly with a liquid comfrey or seaweed fertiliser. 
  • Remove or deadhead the spent flowers, to ensure continual bloom, by cutting them above the first pair of leaves. 
  • You can either leave the tubers in the ground over winter but mulch them well or dig them up and store in a dry, dark place such as a garden shed or garage to protect them from the frost. 

Common Problems  

  • Earwigs like to eat the flowers and leaves.  To control this place small plant pots filled with straw upside down on canes near the dahlias.  The earwigs crawl into the straw in the heat of the day, you can then release them away from the dahlias later. 
  • Slugs love dahlias, so use harmless slug-repellents such as wool pellets, which form a natural barrier to slugs and snails, or copper bands, which slugs and snails hate. 
  • Dahlias not blooming may be due to under watering. 
  • Dahlia tubers not sprouting.  Once planted out, water the compost once, then wait until the first sprouts appear before watering again. 
  • Dahlias wilting.  If its particularly hot, then water more often.

Published: August 2021