I usually plant mine with some good compost mixed in. Also, when the plant is going, I give it a shot of miracle grow liquid when I remember ( about every few weeks). I don't want to give it too much, as it will then get too vegetative and lanky. So much depends on the quality of the soil in which they are planted.

I have not had this experience of "too vegetative and lanky" from fertilizer. I fertilize mine in pots once a week and they get very robust stems.

Usually lankiness is caudes by not enough light.

Actually, lankiness is caused by too much fertilizer.

I agree - I fertilized too much last year and had a good flush of blooms but the stems were pretty weak and flimsy. They didn't do so well after that...

I always intend to fertilize mine, but never quite get around to it, they bloom like crazy. I am fortunate to have pretty good soil, most of my garden has to just make do. As for the leaves curling, I can't say for sure, but it might just be that the weather is just a bit cool & will correct when it gets warmer. Of course it that is the case you probably know by now since this is over 2 weeks since you posted :)

Maybe switch to a fertiliser that's lower in nitrogen amd higher in potassium, to get firmer growth and better flowers?

The best fertilizer is a Blossom Booster. The ratio should be 1:3:2 of N-P-K. This helps form strong bud development which is what you would want. So, yes Ornata is correct; however, the ratio is important.

Thanks,
I'll try the bloom booster since I want Blooms!
The curling leaves started while the plant was potted and indoors so I don't think it had anything to do with the cold. Maybe it was the White flys someone suggested in my other post, since theitr were little gnat looking bugs on my porch where the plants were being kept.
Hopefully the one with the curled leaves will bloom anyways:)
Thanks and Happy Gardening,
Laura

Anyone interested in dispelling fertilizing myths should read this article below. This experimenter proves that:

"Weak stems are not the result of too much nitrogen. In fact stems can be strengthen by fertilizing with additional nitrogen."

My experience has been the same. I use cow manure compost and a fertilize additionally once a week. I get thick strong stems.

Here is a link that might be useful: Mid-Island Dahlia society

Thanks for the link.
Happy gardening
Laura