Hybridizing Dahlias
"....saving seed from the trial garden." Perhaps this is a : "How far does a bee go?" example. Swan Island grows 450,000 dahlia plants on their 40+ acres and the trial garden is on the Southern side and surrounded by their dahlias on three sides. The bee that probably pollinated the Peachy Keen flower , I believe used KA's Bo Peep pollen and those plants were about 10 feet or less away. I did not record the results of the other 10 or so seedlings from that seed package and it may have been interesting had I done that.
This is the flower that Dick Parshall liked in our garden during the tour.
I will sometimes end a varietal row with 2 plants of a seed parent. When I collect these seeds I will note what pollen might have been around it. It has helped me see if some seed parents have "stronger" genetics in form or color or tubers. For example, I might have planted PNC in 3 different spots, kept track of the where the seeds were collected and whose pollen was available. It lead to some interesting findings.
Controlling pollination and keeping good records are important. It is difficult to be successful without both. Repeating your successes or more likely your "almost good" crosses depends on both. If you make a cross that is very good, it is frustrating not to be able make that cross again because you did not record enough information to repeat it. My least favorite quote might go like this: "I saved seed from about ten varieties and mixed them all up into one container. I got a very nice seedling(luck seems to be everywhere) but have no idea which of the ten varieties was the parent or pollen parent."
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Inbreeding in plant breeding is a tool and remember since dahlias are octoploid and have 8 genes for each genetic trait, you would have to inbreed for very many generations before the bad genes would be concentrated and cause problems. You know the answer to the first question: "...be inclined to repeat the same cross for more seedlings with the same parentage...? People continue to do the same thing as long as it gives them good results. If it ain't hurt don't change it! My guess is one generally would not back cross to the parent but would one would not be shy about breeding siblings to each other. But if the parent is one of the best ever examples, why not? The rule of thumb is there is no rule of thumb.
If you look at dahlia breeding from the most simplistic view, the statement: "Breed like to like to get like." is a rule that will work for just about anybody. If you dare to breed "like" to "not like", your first generation seedlings will be generally terrible. But I have observed over the years that many people like "terrible" and seem to embrace chaos as they pursue new dahlias. They say they prefer a chance seedling that has some unpredictable traits and they like that. If you asked them "what is a nice dahlia?" before they bred their flowers they would give a list of their preferences for both form and color. And then they plant these random seeds and these seedlings are their "babies" and they put on their "baby" spectacles and declare that "their baby is not ugly". And as I write this, I have to confess that the tendency to have "baby spectacles" is something that most breeders have. I know Margaret and I have a degree of that when we look at our seedlings. And this "my baby is not ugly" can get you in trouble when you are asked to appraise a seedling. I tend to avoid appraisals unless the flower is actually nice and giving out positive remarks is fun. 
Here is one of our "babies" and we like our baby but do realize that it's future requires other people that would like this flower.
Count me in as … !
Teddahlia people that would like this flower.
I’m hesitant to begin attempts at hybridizing until I have a much better grasp on color and form — “baby spectacles" would ruin any hope for success! As a team, I imagine you and Margaret are excellent sounding boards/guard rails for one another when it comes to seedling evaluation.
Krista I’m hesitant to begin attempts at hybridizing until I have a much better grasp on color and form
Just start. Hybridizing is a series of decisions that makes each program unique but in reality we only get one try each year to roll the dice. Then we wait and tend and protect just to see how the dice land. We evaluate and either choose to move forward with a decision or make a new one the following season.
Lots can be learned during a season but your chance to start only happens once. Better get to it.
Margaret and I used to argue a lot about whether a seedling was good enough to keep. I have shared this before: We allow each other to keep anything we like. We have three categories Ted Likes; Margaret Likes; and Ted and Margaret like and that information is generally recorded in the written remarks. The flower above is/was a Margaret Likes. It will be a third year seedling and it has many versions of this flower and the plants grow 6 feet tall and are vigorous. I cannot remember the tuber production but believe it is good there too. Now I bet Margaret will want to give it a name and then want to sell it too. 
"...but your chance to start only happens once. "
I love the saying: "The longest journey starts with the first step."
Baby spectacles can work the other way too. Once you realize you are overly generous in your appraisals, you may become too picky and cull some really good ones. That has happened here.
And then there is the "failure to appreciate a really good flower" syndrome and it takes a good friend to "wake you up" as to how good a seedling is. This has happened to us numerous times. Get some outside opinions. 
I was just telling my husband that I think I was too critical on some seedlings this year. I let some disappointments (losing some entire seedling varieties to virus) cloud my perspective. I am taking some time each evening to finish organizing all my dahlia images into my Google Drive folders and finding photos of blooms that at the time didn't love. But now, I can appreciate them.
Absence makes the heart grow fonder.
All are seedlings except for Rhubarb & Custard at the bottom.
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Krista today I'm in the midst of one of the key activities of being a "hybridizer".
Germinating saved seeds. It's pretty easy once you get your self in motion. Supplies this year are Dollar store foam trays, paper napkins, indelible marker, stretch-tite and documentation of what I'm doing.
If germination is anything like last year I expect only a small fraction of the seed to germinate.
There's more to the hybridizer story(as professionals so kindly share with us in this forum), but nothing happens to create new Dahlias if I don't do this germination activity. Also, I had to get over my fear of failure and look at this as a fun, exciting activity, with continually learning along the way. I try not to think about the long shot odds of creating a Dahlias that will be the envy of the the Dahlia world
. Luckily I don't depend on this activity to make money for food and shelter.
Cruising through old seedling pictures is heartbreaking for many reasons. If you lost it because it would not make tubers or something like that, you feel bad but that's the breaks in life. But if you see ones that you chose not to keep and now when you look at the picture and remember the flower and see that it was a stupid decision you feel stupid. 
I quit hybridizing dahlias about 30 years ago because it took way too much time to evaluate 1000 seedlings every year and progress them on to the third year. It is a full-time job to plant and evaluate 1000 seedlings every year. Last year it occurred to me that it wasn't necessary to grow 1000 seedlings and I could give myself permission to plant only 50 seedlings So I did some hand crosses last year and planted 50 seedlings this year. I had forgotten what a joy it was to walk around with a morning cup of coffee and look at the new seedlings that were blooming. Out of 50 seedlings I ended up saving five or six to grow the second year. Next year maybe I will plant 60 seedlings!
The question on the table is:
How many seedlings do I need to grow to get
(1) get one nice seedling(2) 5 nice seedlings (3) 25 nice seedlings(4) 100 nice seedlings. ???
When you go into the casino and sit down at the slot machine, they constantly tease you with almost wins. However, you almost never hit the jack pot. When you are breeding dahlias there are lots of "almost wins" and since most of us almost never hit the jack pot and all you get is "almosts" the "almosts" get upgraded by you to "wins" . Yes, no matter how many seedlings you grow you will get some "good ones".
I noticed this as we got to be better breeders. We saved about 10% of the seedlings when were beginner breeders. When we got better, we still saved 10%. And now after several decades of breeding, we still only save about 10%. So if you are like us and and your magic number is 10%, you will have 10% nice seedlings.
As you can tell, I am not saying the 10% you save are "really, really" good seedlings although there may some in there but that you will "like " about 10% of them.
We marked 124 seedlings for retention in 2024 out of about 1100 hopefuls. I can tell you right now that most of the 124 are really not that good despite our initial appraisal. We are just like most people and want to give the ones that could be good a second chance. How many are really, really good ? We will see. 
One of the 10%.
@"Bessie"# What are you going to do when all of those seeds germinate? I would worry that I would have to sell my home and buy a farm in the country so that I could grow them all. 