Ralf, photos might help. It is hard to say, based on your description.

I would add......... curled claw-like distorted new growth is most lieky an excess of nitrogen which can occure as the soil drys out or because you have met the threshold of aditional salts (nitrates), this is easily fixed, usually it disappears, but yes, pictures would help.

HI . As a first time Dahlia grower ,I need some guidance. Crinkley leaves on my plants as well.
These plants are all in 2 & 3 gal pots on a cart.
We water them every day ,feed them with 20-20-20 fert. once a week.
Any help /guidance would be greatly appreciated.

Bill

Here is a link that might be useful: {{gwi:644601}}

Ouch that's a tough picture to look at. I think you should drop the fertilizer and don't fertilize again. 20-20-20 is heavier fertilizer than I use. For reference I planted with Bulbtone the first or 2nd week of June and just fertilized today for the first time. It looks like they have mildew or else the leaves are burned from too much nitrogen - try not to get water on the leaves and try to do your watering in the morning so they have the day to dry out the leaves and stems. Don't water unless the soil is dry at about 2-3" down or the leaves don't bounce back later in the day. Often dahlias will wilt a bit during the hot part of the day but then perk right back up in the evening. So don't water to correct that or they will just rot, only water when the roots need it.

If you can, I would even try repotting them entirely, or move them into a garden to get them out of the soil that is laden with salts. Flushing those pots may help but will keep the tubers wetter than they should be unless you have a very well draining medium.

If the tips are blasted and black you could pinch the tips to encourage new growth. I don't really know if that will help or not. Looking at the photos doesn't help me diagnose the problem, but hearing that you are fertilizing weekly would lead me to believe that the issue is excess fertilizer - which can just burn a plant up.

Hope you get some blooms from them though
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Ok, thanks for the help. I will stop the fertilizer, cut back on the water , repot them if I do not see a difference in a few days.

Bill

HI : Just so you folks will not think I have runined all our new Dahlais.

Bill

Here is a link that might be useful: {{gwi:644603}}

Have you sprayed with any kind of bug spray? I thought of you this afternoon. Yesterday I found 1 dahlia out of all of them that was absolutely covered with little black aphids. I sprayed with an insectidical soap which appears to have killed them. However it also burned the plant and a lot of the leaf area is brown and curling in just 1 day.

If you got any kind of drift of a spray onto the plants that could have had something to do with the leaves. But, - I wish I could send you this privately because I don't want you to feel bad - looking at the gorgeous dahlia in your above photo - look how dark green your leaves are - I think that one is also getting a bit too much nitrogen. Some people think that too much nitrogen will cause the tuber to rot over the winter, so if you intended to keep them you might just drop back to bone meal or something very low N, that also feeds roots and flowers.