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Dahlia overwintering in garden: cut back?

louisenbarberalouisenbarbera Posts: 8
in Plants
Because of the mild winters and low risk of frost I want to keep my Dahlia's in the ground. To limit the risk of frost I want to mulch them. But, should I cut back the stems to ground level before mulching, or can I keep the plants intact and cut them back in spring? Thank you, Louis.
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  • ObelixxObelixx Posts: 30,090
    There will be enough of a chill to blacken the tops at some point over the winter, even here.   That's when you cut them back and mulch them.   Ours get bedding - straw and poos - from the hen shed all year and then an extra blanket of grass clippings from the areas we leave long for wildlife.
    Vendée - 20kms from Atlantic coast.
    "The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
    Plato
  • bédébédé Posts: 3,095
    My dahlias are in pots and are waiting for the first frost.  However with the recent very wet and  windy windy weather they look like I should tidy them away now.

    For yours in the ground, I would suggest cutting the stems back to about 15-30cm. That will serve as a marker and stop mulch blowing about.   Use the tops as the first layer of mulch.  I trust you know that your soil is free draining, as wetness is more of a problem than cold.

    re Obelixx, I'm not sure that I would want rotting grass aroung my next year's emerging dahlias.  But if you have done it in the past ...
     location: Surrey Hills, England, ex-woodland acidic sand.
    "Have nothing in your garden that you don't know to be useful, or believe to be beautiful."
  • ObelixxObelixx Posts: 30,090
    It's not short green grass, but long, dry hay type stuff so doesn't go all slimy.
    Vendée - 20kms from Atlantic coast.
    "The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
    Plato
  • bertrand-mabelbertrand-mabel Posts: 2,697
    Ours are left in the ground and have been for many years. The following year flowers continue to be more and more. We don't add anything and allow them to do what they want. As a child I watched my father take them all up and over winter them and so I did the same when we moved into our home. Disaster the following year...all rotted out. Can't go through that again and so left them in the ground and very pleased with the outcome.
  • Nanny BeachNanny Beach Posts: 8,719
    Mine are all flowering nicely at the moment, I discovered my near neighbours don't do anything with them,no mulching nothing. The ones in pots go into a frost free green house.
  • PosyPosy Posts: 3,601
    If the winter is mild then the only remaining risks are wet and slugs. My heavy clay does not drain well and dahlias can rot if left to it. You also need to keep a watch for slugs eating new growth before it gets going. Down here, slugs are active all year and can destroy a plant coming out of dormancy.
  • JennyJJennyJ Posts: 10,576
    edited October 2022
    I cut one back at the weekend because I wanted to move it and put some smaller plants in its place. It had got huge and flopped over the lawn every summer. It's now at the back of a border on the other side of the garden (should get more sun there as well). I won't be heartbroken if it fails to survive as it's a seed-raised one that I grew maybe 10 years ago. The tubers/rootball was about 40cm diameter and pretty heavy! I don't have anywhere under cover to store such a monster.
    Doncaster, South Yorkshire. Soil type: sandy, well-drained
  • bédébédé Posts: 3,095
    edited October 2022
    Dahlias do need good staking.  I remember the show gardens on Southport promenade years ago, more stake than dahlia. 
     location: Surrey Hills, England, ex-woodland acidic sand.
    "Have nothing in your garden that you don't know to be useful, or believe to be beautiful."
  • FireFire Posts: 19,096
    edited October 2022
    bédé said:
    Dahlias do need good staking.
    Only the larger ones. There is virtue in growing smaller ones like Aruna. Pretty much trouble free, no stakes, no flopping, no breaking.

  • Busy-LizzieBusy-Lizzie Posts: 24,043
    It can depend on your soil, how wet your garden is and how sheltered. Heavy clay and wetness aren't good, but a free draining soil is usually fine.

    I leave dahlias in the ground over winter, but some varieties survive better than others. I have found that Bishop of Llandaff is not a survivor, although Bishops Children are usually OK. Arabian Nights and Park Princess survive for years in the ground.

    I don't cut my dahlias down until they have been blackened by the frost. The stems are like tubes and when cut too soon rain can get down and rot the tuber.
    Dordogne and Norfolk. Clay in Dordogne, sandy in Norfolk.
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