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Dahlias Growing Tall and Skinny over Winter

I planted my first round of Dahlias and left them in the ground (read some stories of people in z6 that leave their's in the ground with no problems). I lost all mine. So this time I built some boxes (12" cubes) and they were gorgeous - the flowers, not the boxes. I brought them inside when the plants had turned brown and before first frost. They are in a slightly heated space (just above freezing) out of the wind and covered. I cut the plants off at ground level when they were brought in. However, they have since sprouted again and are about 6-8" tall. They appear to have stopped growing now that the overnight temperatures have reached freezing. I am wondering if I should cut the shoots off again or leave them? Any advice would be helpful. Thanks!

Comments (17)
  • ken_adrian Adrian MI cold Z5

    pix please ...

    they are a full brilliant sun plants ....

    what if any lights are supplementing the indoor placement???

    you have picked one variable.. temps.. but you are not contemplating the other requisite cultural variables ....

    at some point.. they need to 'feed the tubers' ... for next year ... if you repeatedly let them sprout.. and then cut it all off ... the tubers will not regenerate the stored energy they need ... and no.. you can not provide the food... they need light ....


  • Bruce (Vancouver Island - z8a)


    I don't want the plants to grow at all. I want them to hibernate until I can set them outside again in about mid-April. Should I cut them off and then cover them with black plastic or cardboard or some other material?

  • floral_uk z.8/9 SW UK

    If they are growing you have them too warm and they should be removed from the soil. They need to be somewhere cool but frost free. Don't let the tubers freeze. Clean off any earth and turn them upside down so the cut off stems are downwards to dry off. There's lots of advice available if you google winter storage of dahlia tubers.

    Bruce (Vancouver Island - z8a) thanked floral_uk z.8/9 SW UK
  • tsugajunkie z5 SE WI ♱

    "I brought them inside when the plants had turned brown and before first frost."

    Odd. Mine don't turn brown until after a frost. Rule of thumb I've used for a couple decades has been to let the frost kill them back, cut them off at that time, let them sit in the ground for about two weeks and then dig them. I'll knock most dirt off, put them in peat and then in my basement which is usually around 60*F. Not ideal, but it has worked for me. I don't think your temps are the issue but being in ground is.


    Bruce (Vancouver Island - z8a) thanked tsugajunkie z5 SE WI ♱
  • floral_uk z.8/9 SW UK

    My reading of the OP is that the plants are inside, no longer in the ground. But there was no mention of removing the soil so I imagined them regrowing because they have soil, moisture and excess warmth. I was assuming they had turned brown from cold air even if the ground wasn't frozen. I am surprised 60f works. I would have thought they needed it much cooler to avoid sprouting.

  • ken_adrian Adrian MI cold Z5

    in my ground freeze MI ... my experience is as junkies .... you let them go dormant .... let them dry .. and then store them indoors... bare ....

    if yours continue to grow ... they are obviously not dormant ... so they can not be stored as junkie and i would ... btw .. what the current outdoor temps ... maybe they should go back outdoors to go dormant????

    flora.. in your z8/9 ... how long do they stay dormant ... do you just leave them outdoors upside down???


  • floral_uk z.8/9 SW UK

    They stay dormant until you start them back into growth in the spring. And no, they are definitely not left outside! They'd rot in the rain or turn to mush in the frost. They're stored in a shed or somewhere.

  • dbarron

    Actually long ago (when I used to grow dahlias), I've left some in ground with success. I don't remember % success though.

  • floral_uk z.8/9 SW UK

    Dbarron, I was answering Ken's question about stored dahlia tuber behaviour in my area, not making a blanket statement. Some people can leave them in ground here too if they have well drained soil and live in a mild area.

  • dbarron

    and I was just sharing (what little) insight I have into dahlias.

  • floral_uk z.8/9 SW UK

    Right. I see. I thought you were responding to my comment before yours.

  • gardengal48 (PNW Z8/9)

    Here in my area (which tends to be more uniformly a zone 8 rather than my beachside zone 9) dahlia tubers are often left in the ground...as long as the soil drains well. I've done both but prefer digging and storing - not because of hardiness issues but because our soil is so slow to warm in spring that starting or even growing dahlias in pots gets you pretty much a full month's headstart versus inground planting so flowering is not quite so late in the season.

    Much like Foral, if growing in the ground I let the cold weather knock the plant back and then cut off the foliage at ground level, dig up the tubers, clear or wash off any soil, let them air dry indoors and wrap individually in newspaper and store somewhere cool, dry and dark. If growing in containers, I just skip the intermediate steps and store the tubers in their pots in the same cool, dry, dark siting. Cool is important - not room temp or even at 60F. Somehere around 45-50F is ideal.

    Waiting for a frost to knock them back does not always work here :-) IMO, these are best handled by the end of October or very early November and that is often too early for a frost here. But colder weather will stop new growth and the plant will start to decline visibly and get limp and wilty looking and that's when I cut back and move indoors.

  • geoforce

    Love dahlias but decided anything I have to dig up each fall and store was too big a pain. When I did them though I always dug, dried, then stored in shredded paper or dry sawdust or excelsior. As a sidelight, I haven't seen any actual excelsior (shredded wood for packing) for decades now.

  • Bruce (Vancouver Island - z8a)

    Thanks for all the comments everyone! Gardengal48 is very close to my location and has explained it much better than I did in my original question. Here is some clarification from me in case anyone wishes to comment further.

    1. My tubers are still in soil (in 12" wooden cubes of it)
    2. They were "knocked back" in early November when they were scraggly and ugly but no longer growing (maybe not exactly brown)
    3. Were brought indoors before first frost none-the-less
    4. Are indoors where the temperature is kept no lower than about 2C (36F) overnight but may reach about 5+C (41+F) or higher during the day depending on the outside temperature
    5. Overnight temps probably didn't reach this point until early December (we have only had maybe 2 or 3 nights of frost to date)
    6. Grew to about 8" tall in that time but now appear to be dormant (are still green, but with no further growth, but no wilting either)

    So, should I cut off the 8" stems or leave them and see if they continue growing in the Spring? Actually, here is a further question: When should I put them back outside in the Spring?

    Any further comments would be welcome. Thanks again!

  • dbarron

    I can't say that cutting off living tissue (except to shape a plant in training) has ever helped anything. So, no real reason to cut them off, and if they are your only viable buds, you better not.

    You can't put them out till after danger of frost is pretty much over. You can start them maybe 4-6 weeks earlier inside though if you have a sunny spot.

    Bruce (Vancouver Island - z8a) thanked dbarron
  • Campanula UK Z8

    Water is the trigger for growth (and dormancy), more than heat, I think. I certainly have to allow a number of tender bulbs and tubers die off by stopping all watering...when remaining foliage will turn yellow/brown and drop off...or foliage will persist most of the winter...but this is not good for the plant which inevitably gets all sorts of bacterial and fungal issues. Also, the first spring watering is the trigger which starts resprouting.

    As for dahlias outside, I can leave mine in the ground, no problem...but I do lift a few because the enormous downside of being in the ground is continual snail and slug predation so the plants never get going until really late in the summer whereas a few sy-tarted into early growth in the greenhouse also make terrific cutting material.

    Bruce (Vancouver Island - z8a) thanked Campanula UK Z8
  • cicivacation

    I'm late to this party, but as I store a good many potroots inside at 55-65 degrees each year, perhaps my comments might help a future gardener with a similar 'problem.'

    Humidity is what triggers dormancy; cold temperature just slows growth down.

    When you bring a potted dahlia inside, it will try to keep growing until the humidity of the soil drops down to a certain level. There is no need for concern- just pinch off the unwanted green after it stops growing, as dormancy is important during the winter months. No worries... pinching the growth even a few times will not hinder the tuber's ability to grow in spring when you water it.

    "But I WANT it to keep growing!"
    If you leave the green sprouted late fall/early winter inside, it will not be healthy enough to survive into the next season, even if you water it and provide some light. You need significant grow lights to achieve healthy growth flowering in the winter, with ventilation and fertilizer... but who wants 4 foot plants to baby all winter long, with the associated pests that accompany it? If the answer is YOU, then check out pot growing websites, as they have it down to a fine science and spent a pretty penny on appropriate equipment/supplies. I'd rather pinch now and dream about the outdoor bouquets made along my fence rows in summer...


    Bruce (Vancouver Island - z8a) thanked cicivacation

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