I haven't grown enough seedlings previously to keep a seedling notebook, however I do keep a lot of detailed info on each named variety I grow in a big spreadsheet on Google Drive. Because it's "in the cloud" I can access it from any device and record things like date of first bloom right out in the dahlia patch super easily and the updated data is there the next time I look at it on my computer. When I start a new year on my spreadsheet I log date of first bloom for each year I've grown that cultivar so just at a glance I can see a lot of information about everything I grow.
This year I'll have to add a seedling spreadsheet!
I log ADS class numbers when applicable for each variety too, which comes in handy for filling out my tags at dahlia shows. I don't have to keep looking everything up in my classification handbook. All this logging is a decent amount of work upfront but it sure is nice to just be able to pull my phone out and update something in 1 minute.
