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I am trying to start off dahlia tubers and have them sitting in trays on top of damp compost in an unheated greenhouse.

They've been there for a month and I thought they'd have shooted by now.

Can anybody tell me what I'm doing wrong ?

Any suggestions would be appreciated.


Alina W

Try burying them slightly, so that the tubers are covered - they may not be re-hydrating enough.

Hi Chris, I start mine off in March in terracotta pots in the garage. Planted quite deeply in damp compost. Usually they are fine for planting out in June.

Tee Gee

I am looking for clues

You say you have them sitting in trays on top of damp compost in an unheated greenhouse.

Are they new tubers or tubers you have saved through the winter?

If new! then it might be too cold for them and it all depends on how damp is 'damp'!  If they are too damp this can make things cooler still, I have an expression to describe this and that is they want to be the damp side of dry if that makes sense!

If they are saved tubers how did you keep them through the winter?

They've been there for a month and I thought they'd have shooted by now.

I would have thought so too!

There are some pictures here on how I do it;

ive left mine on top of my kitchen cupboards in an old fruit tray. they have started to shoot. the trick i was told by my father in law. is to dry them out thoroughly and slow introduce them to warmer outside temp. or as i have done in your kitchen. damp soil and cold temps wont allow them to start. they may still even rot.



I pot mine up in the house and keep the compost just moist and I generally get enough shoots to take a few cuttings.  The ones I left in the greenhouse sadly turned to mush.  Give the tubers a squeeze and make sure they're still firm and if they are, pot them up and move them somewhere a bit warmer.


Many thanks for all your help.

Ive had to remove a few tubers which are rotten,  but the majority are fine.  I think that the shed (where I keep them) is currently too cold during the night.  I'll move them inside the house (My wife won't like it though !)



I have sown some dahlia seed and bought some nice plump firm tubers. I am going to sow more seed in a week or so (kitchen windowsill job) I may plant the tubers at the same time (do you always leave the top of the tuber poking out of the soil?). I may even try some cuttings aswell (going to have to be brave). 


What is the point of taking dahlia cuttings? The tubers that I dug up last year are so big that I can divide them into 3-4 clumps, each with at least one shoot. That alone gives me so many plants that I don't have room for them all. Not criticising, just wondering?


Some dahlia tubers aren't that big and will not divide and then some people are reluctant to do the chop-perhaps the cutting route is the safer option??


If you're buying new, like me, and want to increase your stock rather than pay for lots of tubers, taking cuttings is an excellent option.   


Yes, I see the point now. I might give it a try just for the hell of it, but I never seem to have much success with cuttings except for pelargoniums, they always seem to die on me, either dry out or rot, grrrr!

Discodave, you mean to plant the tubers indoors don't you, in pots? I cover the whole of the tuber but let the stem peak through. Covering the tuber protects against cold and stops it drying out. I pot up dry....dry compost.....for a few days and then lightly moisten the soil. Works well for me.

I'd say that they need to be half buried at least and def warmer than the 8 degrees it currently is outside!

I've some tubers bought and some saved. Should tubers be planted now and kept indoors then? The destructions which came with the bought dahlias says plant in April?



Yes Verdun, I meant plant them indoors in pots to start them off. I can put them in my  house then put out into a cold frame or plastic greenhouse when it warms up

Well, if tubers were bought now I think they're better off planted in dry compost than leaving them in their polythene packets in overly-warm conditions indoors. The dry compost protects the cover them totally, as I said earlier, only mosten compost when temperature rises. If its still cold cover with fleece

 I find the slight dampness thats in the compost bag seems to be enough to start them off,then do what u will,,cuttings or otherwise,,


Ok, will do them today. 

My unseated greenhouse had temperatures falling to -2 deg C during the nights this week. It may be too cold.