The question of whether 'blown centers' result from genetics, or from environmental factors, was recently the subject of an interesting conversation in another thread. Now...how about 'weak stems.' Nature (genetic) or Nurture (environmental factors).
We have had an unusually wet summer here in Upstate NY; great for our dahlias, generally, but I'm seeing more weak stems than previous summers. So I'm just a-wondering...
Nature or Nurture, again...
Stressed dahlias exhibit many bad traits. Seedlings are generally not in "stressed" situations and should have nice centers. Bad centers are the number one reason we cull flowers. That even extends to the "2 day center" where the flowers are nice for a couple of days and then open the center while the rest of the bouquet has nice centers.
cmcramer on a YouTube video the presenter was giving a tour of his Dahlia growing garden and mentioned a particular variety had weaker stems than he liked. He mentioned giving it a "potassium treatment". Potassium is a water soluble element, so possibly the rain has leached that out of your soil this year.
One commercial cut flower grower adds potassium sulfate to his garden in August each year.
One thing growers don't pay attention to or make note of is what progression of bud development is flowering. Did they miss the primary and secondary blooms off the main flowering stem and are trying to harvest the third or even forth flower to bloom? Each subsequent flowering is on thinner and weaker stems.
British show growers only harvest the first blooms and they control number and size of the blooms by growing the plants with more or fewer flowering stalks. David Spencer said he grew one 11 up and another 15 up and so on. I never do this as I am Finnish not British. 
Teddahlia A bit of both here so I can pick and choose . But the Finnish is about 7 generations back and the Brittish only 2. When it comes to growing though...wait! DId Finland have dahlias 7 generations ago? I highly doubt it.....
Not many dahlia growers in Finland.
12 days later
Potassium sulfate experiment comin' up 2024!
Fertilizer thoughts: Azomite is also on the list as a supplement for many people. It has a lot minerals and I would not be surprised if the minerals and micro nutrients in it would super charge your garden soil. Perhaps it would return the soil to what it was before you grew in the same place for over 10 years. However, if your issue is with excess phosphorus because you used those "more bloom" fertilizers or just as bad used "low nitrogen fertilizers" that many people recommended or you have been using bone meal, you have to remove the phosphorus from the soil by removing plant material such as dahlia plant stalks. Phosphorus does not get washed out in rain water and you have to remove it by growing a crop that you remove from the garden and the phosphorus is in the plant material you remove. And it goes without saying that you must stop using all phosphorus fertilizer including the worthless bone meal. You may help with the excess phosphorus issue by being perfect with your soil pH as a perfect pH allows the plants to absorb the most fertilizer. Phosphorus can inhibit the uptake of fertilizer: " The main symptom of excessive phosphorus in soil is stunted plant growth. High P interferes with N absorption." Removing phosphorus may take you several years.
10 months later
- Edited
I know this is an old thread, but is this why some folks give an 'epsom salts' treatment to perk up their dahlias? I know it's high in magnesium but might it have some potassium too? When I did it one year it made the foliage color up nicely and not look so anemic.
I'm interested in finding a source of potassium or some source of micro nutrients for the dahlias, and I'm pretty sure that our hardware stores don't carry azomite or potasium sulfate; i'd have to mail order for either of those,. Would it be too late to use it now anyway? August is half over already.
Epsom salts cause dahlia to make more chlorophyll. Banana peels have lots of potassium.
Dahlia53 since you haven't had a reply for a potassium source, here's a product I put in my Amazon Gardening Wish List a few months ago. Not sure I'll purchase it.
ALL- NATURAL MURIATE of POTASH | POTASSIUM FERTILIZER with 0-0-60 ANALYSIS https://a.co/d/bdfpwAh
14 days later
ReNForce K was recommended to me by an Australian grower. I've not been able to get my hands on it, but his dahlias are pretty incredible. Still looking!