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Overwintering Dahlias


Firstly, I am a inexperienced gardener with regards to plants. So if anyone can give me some advice please make it simple so even I can understand. Thank you.

I have 30 Dahlias in individual 20cm (8'') pots. I bought them as bedding plants from a supermarket & I have a great display from them all Summer long.

Two days ago I read an article - Daily Mail - by Monty Don; 'How to make your Dahlias last forever'. He said it should be possible, after the first frost, to cut the plants down to ground level, cover them in a mulch & leave them insitu. in the garden throughout the Winter.

I intend following this advice but bringing pots under my car port which is always a few degrees warmer than outside. However, the MD article mentioned Dahlias tubers. My plants were bought as bedding plants, they were not tubers. I need the following advice;

1 - Are there two types of Dahlias? One with tubers that can be overwintered & one without that can't?

2 - Or, do the non- tuber Dahlias develop tubers as they grow?

Forgive the naivety but it seems silly to me to try & overwinter something that will die anyway.

I hope I have explained this correctly.

Dahlia experts please help!




  • fidgetbonesfidgetbones Posts: 17,590

    Seedling dahlias will develop tubers by now. If you gently knock them out of the pot, they will be pressing on the edges of the pot by now.

    You can leave them in the ground but it depends on where you live. Here in the midlands they usually freeze and die. Last year they didn't but the slugs got them as soon as they grew in spring. I usually lift mine, and store the tubers in old compost in a frost free greenhouse.   You could store in the pots, but is essential that they do not freeze.

  • This is only the second time I have tried dahlias. The first time, the tubers were very scrawny and rotted away to nothing very quickly. What would be a good feeding regime to ensure good sized tubers go into winter store? I have 3 dark-leaved plants from the 'Happy' series and have been feeding weekly with liquid tomato food, plus a monthly boost of liquid seaweed/iron.

    Also, I still see comparatively recent articles recommending the use of sulphur-based products to stop the tubers from rotting while in store, but it seems that most have been banned for garden use. Is there any alternative?


  • fidgetbonesfidgetbones Posts: 17,590

    Flowers of sulphur is traditionally used to dust dahlia tubers with, after drying off by cutting the tops off and laying on one side.If you google it there are plenty of suppliers on amazon. I dont use anything and  at least 90% usually survive the winter. I pot them up into fresh compost when they start growing.

    I've never had any problems with tubers forming. I mix in blood fish and bonemeal at planting time and then let them get on with it. Its too late now to make any difference this year.

  • Thanks, fidgetbones.

  • Dahlias growing in pots are going to be vulnerable to freezing if left outdoors, and if the tubers freeze they will rot and die.

    I leave my dahlias in the ground, mulch them well and hope for a mild winter.

    If my dahlias were in pots I would wait until the first frost blackened the plant, cut them back to a few inches, put them on their sides to let any water in the hollow stems drain away and then store them somewhere frost free, keeping the compost pretty dry, until next year when they could be planted out after the threat of frost has passed. (If you have the space in a greenhouse/conservatory etc, you can bring them into growth earlier, but you cannot plant them out until the risk of frost has passed)

  • YviestevieYviestevie Posts: 7,063

    I live in the west midlands and for some reason my Dahlias are fine when I leave them in the ground.  They have been in situ for around 3 years and I dont do anything to them.  They are in reasonable soil (not waterlogged in Winter). That said, they will now probably all die this winter.

    Hi from Kingswinford in the West Midlands
  • HmsHms Posts: 5

    I have just over wintered dahlias and some are like dried prunes dry and wrinkles is there a cure or is this how they go,it's rather cold in edinburgh. As you can see I am a newcomer to gardening.

  • Hostafan1Hostafan1 Posts: 34,876

    Hms, give them a light watering which will re-hydrate them and start them off, but don't totally soak them

  • I live in Scotland and although my garden is south facing we do get a lot of rainfall in central area so I usually dry  my dahlia tubers in my walk in greenhouse to enable them to dry out naturally before I store them in fleece and compost before I store them in the attic. I can't leave in the ground or apply mulch as the rain would rot the tubers as I have heavy clay soil.
  • hi I have just bought some dahlias and I know it’s late in the day to plant so can I keep the packs in the dry in my shed until next spring. I am experienced in gardening in my own humble way but cannot get advice on the web about storing. Thank you
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