How to increase Dahlia seed production?

Now you know why hand crossing is tried by many and done by few. Kristine Albrecht's book on dahlia breeding has everything in it that will give some results and in many cases good results. Margaret always removes the ray florets from her mother flowers. It is all in the book and the book was edited by a world famous plant breeder.

As far as getting seeds from difficult varieties that are bee crossed, I used to scoff at the removal of the ray florets as not being effective. It is actually about the only thing that works even if it only marginally increases the number of seeds. Let me re-state that: 5 or 6 seeds are a lot better than 1 or 2 or none. Yes, most seed pods will still yield nothing but there will be more with a few seeds. Most varieties do not need floret removal and make plenty of seeds. It is varieties that you know are capable of making seeds but seldom make any that benefit. Some varieties never make seeds at all. Show N Tell is one and I have checked many hundreds of flowers for seeds and removed florets and never ever got even one seed.

Rahlia as Teddahlia explains, hand pollination can be very frustrating.
Here is a past discussion that may be more information than you are interested in:
https://forum.dahliaaddict.com/d/185-hybridizing-dahlias-/102

Off the top of my head, below are a few variables to consider in producing seed.
What gets the flower to make seeds?
Quantity of stigma present ( some dahlias produce lots of stigmas, some almost none)
Stigma receptive to receiving pollen ( mature and chemically ready for fertilization)
Pollen viable and mature ( moisture is said to kill pollen, pollen has limited life span without special storage techniques)
Temperatures and humidity that are favorable to pollen survival and germination on the stigma (too dry and hot is not good)
Sufficient time for seed pod to be on the plant, to enable maturity ( this varies by type of flower)

Patience and persistence of the hybridizer:
Reapply pollen several times over the lifespan of the open flower, to enable getting stigmas that are receptive to pollen

Once pollen germinates on the stigma:
Does the pollen have enough vigor or life span to make it to the ovary of the floret (think variability of floret depth)
Does the genetics of the pollen and seed parent "match up", to allow a viable seed to form ( @Teddahlia always says breed like types for best results)

Once a seed is formed:
Is there an embryo in the seed (tiny leaves and root radical)
Is there enough "energy" in the seed itself to support germination
Are the conditions of temperature and moisture sufficient to enable seed germination

Not meticulous and persistent enough is the simplified answer. A bee pollinates flowers all day long and several other bees do the same. A flower in the garden may have over a 100 visits per day from bees. And there are other pollinators too like the small sweat bees. I believe that most breeders have abandoned hand pollinating because it is too much work. They prefer to focus the bees to use the right pollen on the mother flower. They do this in several ways and the easiest is called an isolation bed where only the flowers you want to cross are grown well away from others. The late Mike Iler was one of the first to do them although others probably have done it but Mike was good at it. He used flowers of the form he wanted to breed ,planted together about 100 feet away from his main garden. The flowers in the bed included varieties that never made seeds but did make pollen and of course several known seed makers. Mike had been a hand crosser of not only dahlias but also previously was an Iris breeder. He preferred doing the isolation beds. over hand pollinating.

Rahlia Could shaving the ray-florets (petals) and pollinating the ray-florets be helpful?

This is a method I was taught when learning to breed dahlias. My father would use scissors to cut off the ray florets to just above the stigmas and then brush these with pollen several times a day,

As mentioned previously, the most important thing to do is to pollinate the stigmas several times per day for several days. The stigmas are only receptive to pollen for hours, not days, so timing is important. That's why hand crossing is such a PIA lot of work.

Hand pollinating dahlias is a lot of work done properly. I personally won a medal with a flower I hand pollinated. It was the last one I ever did as it was too much work. Some people like meticulous time consuming tasks that give you rewards. Margaret has the patience and persistence and attention to detail to do it. I do not. There is a long list of breeders that tried it and quit. My favorite successful hand pollinator was the UK breeder, now deceased, Ken Stock. He explained the process in exquisite detail and personally had results that made people envious. Despite all the years of his successes and showing pictures on his website and entering in trial gardens, very few people became hand crossers.
Note: I am not allowed to share Margaret's specific procedures. If I did I would no longer be living in this house. She says they can read Kristine's book and there is enough info in there to be successful. After all , when Kristine visited our garden way back when , Margaret showed her how she did it.

SteveM

SteveM by only receptive to pollen for hours do you mean only a few hours per day when temp and moisture levels are ideal. OR only a few hours period/ a few hours total in the entire life cycle of that bloom? Like there is such a small window of opportunity and if you miss time it it’s just gone? I would wait for flower to open, flower to make pollen, then finally for the stigmas to look sticky if that makes any sense. Maybe some I did before they were looking sticky in “now or never” type of situations like I was getting ready to leave for a trip. Do all the stigmas go into “ready for pollen acceptance” mode at the same time? Or is it a staggered event?

Bessie

I had one dahlia bed that had afternoon shade. Another dahlia bed in a different part of my yard was in full sun. I would see tons of bee action in the sunny part of the yard and think “perfect time to do some hand crossing”. I would then make some crosses in both the sunny dahlia bed and the shady dahlia bed.

One plant I focused a decent chunk of time into crossing (ivanetti) was in the shady dahlia bed. I hand crossed it with 4 different varieties and it made me zero seeds. I’m wondering now to myself if this could be due to cooler temps during crossing since it was in the shady bed or if it just doesn’t make seeds, or if it just doesn’t make seeds with the flowers I tried to pair it with. In my mind bees out = good temps and timing for hand crossing. But I guess I should have thought about the different mini temperature zones within the yard.

However when those same crosses were reversed and ivanetti was the pollen parent instead of seed parent 2/4 of the other plants all located in the sunny bed made (what appears to me) to be pollinated seed.

Then again I’ve had this same scenario happen with my full sun plants I crossed as well. Cross a pair both ways so each one has chance to act as seed and pollen parent but then only one plant makes seeds. Maybe I’m in denial because I love ivanetti and wanted seeds from it. I will relocate all my plants to full sun next year and see if that changes anything. Also I’ve said before a good chunk of my crosses were not even close to ideal situations. Limited pollen, not repeating the cross multiple times, it’s my first year attempting this, etc. Soooo has anyone gotten seeds from Ivanetti ?

Ivanetti is one of the several sports of Cornel and it was hybridized by Cor and Nel Geerlings of the Netherlands. I am no expert on them but Cornel Bronze, Ivanetti, Isabel, Caitlin’s Joy, are some of them. For many years breeders shunned Cornel as a seed parent and I do not remember why but I tried it years ago and nothing came of the seedlings. Rivers Dahlias used it as a seed parent and got Rivers Yellow Snow. I have yellow snow but it's seed production is terrible. I believe Jowey Dahlias from Europe used Cornel in his breeding program and many nice flowers were released. I grew Joey Frambo and It was very nice but not a good tuber maker for me and I lost it.
https://library.floretflowers.com/products/dahlia-jowey-frambo

SteveM oh that makes a lot of sense now. With the hand crosses I attempted a lot of the time when opening the seed pods there would be no seeds on the outer most layers and then seeds only near the very center. But all the videos online showing harvesting seeds with open pollination you see seed right on the outer most layers of the seed pod. Which makes sense because my timing was pretty random and I didn’t repeat many crosses multiple times or multiple days

Teddahlia I personally liked Ivanetti because it seemed so durable and productive compared to the other plants next to it. I assumed since Cornel makes seeds Ivanetti probably would also, or is this a toss up with sports?

Teddahlia I’m now realizing I should have used open pollination to get more stats on who makes seeds THEN use that info to go into hand crosses…more learning and ideas for me for next year I suppose

" I assumed since Cornel makes seeds Ivanetti probably would also, or is this a toss up with sports?"
Cornel was a very below average seed maker for me. When we grew Ivanetti, I do not remember getting seeds. but that was 20 years ago. I always personally thought Ivanetti was a great tuber maker but I never liked the maroon color. It is a fact that ball dahlias in general do not make very many seeds. Snoho Doris was used as a seed parent by some people . I cannot think of any ball that make lots of seeds or even an average number of seeds. 20th Ave Old Major is a personal favorite ball and in the three years of trying I got zero seeds. It's breeder says he gets a couple seeds each year. I doubt it.

Teddahlia your info gives me breadcrumbs that fuel my hope of what might give me seeds.

Teddahlia I cannot think of any ball that make lots of seeds or even an average number of seeds

SB’s Ora was a slightly above average seed producer for me. (Haven’t grown any of them out though).

I was able to get a decent number of seeds off both Brown Sugar and Copper Boy this year.

I was discussing actual ball dahlias and seed production. Miniature ball dahlias make many more seeds for me and the ball seedling I got this year has a miniature ball grandparent and formal decorative parent. I have no problem getting lots of MB seeds every year. Having said that , I only use our own intros for seeds.(three are medal winners and all make seeds ).