It is almost certainly because you are trying to grow it indoors. Dahlias grow well perfectly well outdoors here and that is where yours should be. Can you show a picture? It sounds as if your dahlia has grown weak and spindly from being inside and has just keeled over under its own weight perhaps coupled with some overwatering issues. Putting it outside without hardening it off will not have helped. Dahlias flower here in late summer so trying to force it isn't a good plan.

Thanks for the reply, i didnt put it out due to the weather i just thought with it being in a pot it would just get over watered due to rain. I did attach pic it hasnt gone on i will try again.

What is hardening off? Sorry im pretty much a novice and was just happy to see growth.

No, I promise you the weather would not trouble your dahlia at all. They are not frost hardy but they are absolutely fine in any weather our U.K. summers can produce. And in a pot it will be highly unlikely to get too much water, however much it rains, due to the small surface area. You are more likely to need to water it.

Hardening off is gradually introducing a plant to outdoor life, with its sun, wind, rain and variable temperatures, starting with an hour or so and increasing the time outside each day until it is out all the time.

This website is handy and the little video at the end explains how to grow dahlias in the ground or in pots. https://www.vanmeuwen.com/how-to-grow-dahlias

Thats good to know, thank you. I always worry about too much rain for plant etc with our weather. if i had potted my tuber up and left it outside, i guess the hardening off would not apply? i cant seem to upload a picture here for some reason. Wish could get an idea if it can be salvaged.

My guess would be either the tubers are rotting or you have a borer in the stems.

Thank you, Any advice on what options i have with plant?

Unfortunately it looks pretty leggy and weak. Dahlias don’t do well under grow lights long term, they need sunlight and a lot of it! Hardening off means gradually putting it outside a little bit longer each day until it acclimates to being in the sun and wind.

What if i chopped it to the bottom? And put it back out? Do you think that could help it Regrow healthier, Or is that tuber long past surviving? I dont know if i should give up on it or is the tuber able to be saved and replanted? If not now then maybe next year.

Oh dear, Farrah. That looks pretty dreadful, I'm afraid. It's badly stretched and weak through lack of light and probably excess warmth. Google 'etiolation'.

If that were mine I'd stick it outside and ignore it. I wouldn't cut it down. It might put out new sprouts from the tuber as long as it hasn't rotted. I'm assuming there's a drainage hole in the pot? Or it might die. Not much you can do to influence what it does at this point.

btw there are no borers in the U.K. which attack dahlias. And don't worry too much about the comment above about needing lots of sun. They do need plenty of light but they are perfectly happy with our overcast skies. It doesn't have to be bright sunshine. Our weather suits dahlias fine. Plenty of rain and no extremes of heat.

And yes, you could have just potted it up and put it outside. It would have been much happier.

There are plenty of growing dahlias in the garden centres if you want a quick cheat replacement. You could probably even start new tubers if you can find any still available.

Lol, honestly it wasnt as bad as this, but yes as much as i may be embarrassed about putting that out in the garden i may have to. It does have drainage holes, just the standard ones of the pot. i suppose cutting off the stems shouldnt affect it? I guess if its alive there would be new growth, without the dead looking foliage on top lol. Unfortunately i dont have much of a garden which is why i was resorting to planting tubers in a pot. The bit of sun i get is the front garden which is south facing. i also have some double begonia bulbs in a pot, i best move them out too do you suggest to acclimatise these too? I also had potted up some calla lily that actually seems to be doing ok but i am thinking of moving that out too with better weather predicted.

Thank you all, i think i will cut off the limp leaves on the dahlia and put it outside and see if this does anything.

I will update in about a week

Not sure if anyone interested but i thought an update may help other novices like me. So considering i had let myself believe i had killed my dahlia plant, i decided to chop the stems rights off to the bottom set of leaves which looked best out of the rest. The weather here in the uk has been nice for me to leave the pot outside in my north facing garden which gets a little bit of sun. My way to acclimatise, its probably wrong but its been working! I have new growth, i havent watered it just the natural rainwater which we had a fair bit of when it was put out. But it seems to be showing signs of growth. I have moved it to south facing garden now for more sun to see how it gets on. Fingers crossed! I will probably only leave here for a day or two while sun and temps are reasonable, then move back to north facing garden as on real hot days the sun hits hard.

Well done. Now you know for next year that they do not need to be kept inside and that they are totally happy outdoors in this country.

Thanks for taking the time to come back and give an update. It's helpful to people seeking advice for similar questions. Well done!