I bought some seed a few days ago, @TreeClimber
- I picked them up on ebay, though you should be able to find them from more, um, reliable online stores. I am also pretty sure that I saw a Burpee seed pack at Lowes.
This isn't first hand knowledge - it is what I plan on doing based on reading.
I plan on planting the dahlia seed on a couple of 1020 flats with an inch between seeds. I will gently press the seeds into the soil and thing apply a light dusting of soil over the top of the entire 1020. Water it and keep it warm with 75 degrees being my target. Germination is supposed to be 7-12 days later.
The seedlings will be allowed to grow until they are touching one another - brushing shoulders. I will then transplant the seedings to individual 3.5" pots which I will rack in yet another 1020 flat (18 of the pots will fit per flat). They'll stay potted for the rest of the season unless they seem too cramped.
FWIW, I plan on making the soil in the pots a 50/50 mix of peat moss and potting soil. I am doing this to help manage moisture to a certain degree, but primarily because I intend to over-winter my roots in the planters. (Which may not work out - it is an do-nothing experiment.)
In the fall I will cut away surface vegetation and stack my flats up in the garage (which stays near 43 degrees through-out the winter). I *might* recover a few of the tubers and bag them up, but the plan is to break them out of the planters in spring 2021 and plant the roots / tubers. They will probably all still be mysteries as they are not likely to flower in 2020.
When you are planning, I think that you should decide pretty early on how many of the flats filled with 3.5" pots you want to wrangle. I am going to plan on 4 or 5 of them, dependent in part on how well or poorly the seedlings perform.
I also think that you probably need to temper your expectations. I hope to get about 70 plants to a flowering stage by 2021. I anticipate that less than 10 of these will be something that I will want to propagate to year 3 and then other annual cullings will happen. Keep an objective eye and work towards excellence.
EDIT: I failed to explain my reasoning for growing in pots. I don't care to scrabble for the roots as they will be fairly modest in size and probably easy to damage in such an immature state. Using the pot gives the seedlings the best chance to reach maturity.